Quantum dot light-emitting devices and electronic devices

Abstract

This invention relates to quantum dot light-emitting devices and electronic devices. The quantum dot light-emitting device includes: a first electrode and a second electrode, a quantum dot layer between the first electrode and the second electrode, and a first electron transport layer and a second electron transport layer disposed between the quantum dot layer and the second electrode. The second electron transport layer is disposed between the quantum dot layer and the first electron transport layer, wherein both the first electron transport layer and the second electron transport layer comprise inorganic materials. The lowest unoccupied molecular orbital energy level of the second electron transport layer is shallower than the lowest unoccupied molecular orbital energy level of the first electron transport layer, and the lowest unoccupied molecular orbital energy level of the quantum dot layer is shallower than the lowest unoccupied molecular orbital energy level of the second electron transport layer. The electronic device includes the quantum dot light-emitting device.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to, and all benefits arising therefrom, Korean Patent Applications Nos. 10-2019-0129887 and 10-2020-0133002, filed with the Korean Intellectual Property Office on October 18, 2019 and October 14, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] A quantum dot light-emitting device and an electronic device including the quantum dot light-emitting device are disclosed. Background Technology

[0004] The physical properties of nanoparticles (e.g., band gap, melting point, etc.) and other inherent characteristics can be controlled by changing the particle size. For example, semiconductor nanocrystal particles (also called quantum dots) exposed to light energy or electric current emit light at wavelengths corresponding to the particle size of the quantum dots. For a material with a given composition, the wavelength of the emitted light depends on the particle size, and quantum dots with relatively small particle sizes emit light at shorter wavelengths. Therefore, quantum dots can provide light in a desired wavelength region by adjusting the particle size. Summary of the Invention

[0005] Quantum dot light-emitting devices, including those using quantum dots as light-emitting elements, and methods for improving the performance of said quantum dot light-emitting devices are of great interest and are described herein.

[0006] The implementation will provide a quantum dot light-emitting device that can achieve improved light-emitting performance, for example, at least one of the following: higher external quantum efficiency, lower driving voltage for a given brightness value, or improved lifetime.

[0007] The implementation will provide an electronic device including the quantum dot light-emitting device.

[0008] According to an embodiment, a quantum dot light-emitting device includes: a first electrode and a second electrode, a quantum dot layer between the first electrode and the second electrode, a first electron transport layer and a second electron transport layer disposed between the quantum dot layer and the second electrode, wherein the second electron transport layer is disposed between the quantum dot layer and the first electron transport layer, the first electron transport layer and the second electron transport layer each comprise an inorganic material, the lowest unoccupied molecular orbital energy level of the second electron transport layer is shallower than the lowest unoccupied molecular orbital energy level of the first electron transport layer, and the lowest unoccupied molecular orbital energy level of the quantum dot layer is shallower than the lowest unoccupied molecular orbital energy level of the second electron transport layer.

[0009] The energy difference between the lowest unoccupied molecular orbital level of the first electron transport layer and the lowest unoccupied molecular orbital level of the second electron transport layer can be from about 0.01 eV to about 1.20 eV, and the energy difference between the lowest unoccupied molecular orbital level of the second electron transport layer and the lowest unoccupied molecular orbital level of the quantum dot layer can be from about 0.01 eV to about 1.20 eV.

[0010] The energy difference between the lowest unoccupied molecular orbital level of the first electron transport layer and the lowest unoccupied molecular orbital level of the second electron transport layer can be from about 0.01 eV to about 0.80 eV, and the energy difference between the lowest unoccupied molecular orbital level of the second electron transport layer and the lowest unoccupied molecular orbital level of the quantum dot layer is from about 0.90 eV to about 1.20 eV.

[0011] The lowest unoccupied molecular orbital energy level of the first electron transport layer can range from about 3.2 eV to about 4.8 eV, the lowest unoccupied molecular orbital energy level of the second electron transport layer can range from about 2.8 eV to about 4.2 eV, and the lowest unoccupied molecular orbital energy level of the quantum dot layer can range from about 2.5 eV to about 3.6 eV. Furthermore, the above ranges of energy levels take into account that the lowest unoccupied molecular orbital energy level of the second electron transport layer is shallower than that of the first electron transport layer, and the lowest unoccupied molecular orbital energy level of the quantum dot layer is shallower than that of the second electron transport layer.

[0012] The first electron transport layer may include first metal oxide nanoparticles, and the second electron transport layer may include second metal oxide nanoparticles that are different from the first metal oxide nanoparticles.

[0013] The first metal oxide nanoparticle and the second metal oxide nanoparticle may each have an average particle diameter of less than or equal to about 10 nm.

[0014] The inorganic material of the second electron transport layer may include cerium oxide, strontium titanium oxide, niobium oxide, barium tin oxide, or a combination thereof.

[0015] For example, the second electron transport layer may include cerium oxide nanoparticles, strontium titanium oxide nanoparticles, niobium oxide nanoparticles, barium tin oxide nanoparticles, or combinations thereof.

[0016] The second electron transport layer may further include an n-type dopant.

[0017] The n-type dopant may include alkali metals, Sn, Ni, Co, Mo, V, Ga, Mn, Fe, Nb, Sr, Ba, In, Ca, Zr, W, Ti, Y, Al, or combinations thereof. Furthermore, the n-type dopant may be included in the form of metallic elements, metal compounds, metal salts, or combinations thereof.

[0018] The second electron transport layer may include cerium oxide and cesium, with cesium in amounts ranging from 2 atomic percentages to 16 atomic percentages, based on the total number of cerium and cesium atoms in the second electron transport layer.

[0019] The n-type dopant may include Cs, Rb, Li, Na, K, or metal salts derived from the following: cesium carbonate Cs2CO3, cesium phosphate Cs3PO4, cesium vanadate Cs3VO4, cesium azide CsN3, lithium nitride Li3N, and rubidium carbonate Rb2CO3.

[0020] The second electron transport layer may include cerium oxide and cesium salt, and cesium may be included in an amount of about 0.01 atomic% to about 40 atomic% based on the total number of cerium and cesium atoms in the second electron transport layer.

[0021] Based on the second electron transport layer, the n-type dopant may be included in an amount of approximately 5 vol% to 40 vol%.

[0022] The first electron transport layer may include first metal oxide nanoparticles, which include at least one selected from the group consisting of Zn, Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, and Ba.

[0023] The first electron transport layer may include Zn 1-x Q x O represents zinc oxide nanoparticles, where Q is a metal other than Zn, and 0 ≤ x < 0.5.

[0024] Q may include Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Si, Ba, or combinations thereof.

[0025] The first electron transport layer may include Zn 1-x Q x The zinc oxide nanoparticles represented by O, wherein Q is Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Si, Ba, or a combination thereof, and 0 ≤ x < 0.5, the second electron transport layer may include cerium oxide nanoparticles, and the zinc oxide nanoparticles and the cerium oxide nanoparticles may each have an average particle diameter of less than or equal to about 10 nm.

[0026] The second electron transport layer may further include cesium, cesium salts, cesium carbonate, or combinations thereof.

[0027] The second electron transport layer may have a thickness smaller than that of the first electron transport layer.

[0028] In one aspect, the quantum dot layer comprises cadmium-free quantum dots, and the quantum dot layer emits light having a peak emission wavelength region of about 430 nm to about 480 nm.

[0029] According to another embodiment, an electronic device including the quantum dot light-emitting device is provided. Attached Figure Description

[0030] Figure 1 A schematic cross-sectional view of a quantum dot light-emitting device according to an embodiment, and

[0031] Figure 2 Display representative Figure 1 A schematic performance level diagram of the quantum dot layer and the corresponding energy levels of the first and second electron transport layers of a quantum dot light-emitting device. Detailed Implementation

[0032] The invention will be described more fully below with reference to the accompanying drawings, in which various embodiments are illustrated. However, this disclosure may be embodied in many different forms and should not be construed as limited to the exemplary embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. The same reference numerals throughout denote the same elements.

[0033] It will be understood that although the terms “first,” “second,” “third,” etc., may be used herein to describe various elements, components, regions, layers, and / or parts, these elements, components, regions, layers, and / or parts should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or part from another. Therefore, without departing from the teachings herein, the “first element,” “component,” “region,” “layer,” or “part” discussed below may be referred to as a second element, component, region, layer, or part.

[0034] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a” and “the” are also intended to include the plural forms, including “at least one”, unless the context clearly indicates otherwise. “At least one” will not be construed as limiting “a”. “Or” means “and / or”. As used herein, the term “and / or” includes any and all combinations of one or more of the associated enumerated items. It will be further understood that the terms “comprising” or “including” as used in this specification indicate the presence of the stated features, regions, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more additional features, regions, integrals, steps, operations, elements, components, and / or sets thereof.

[0035] Furthermore, relative terms such as “lower” or “bottom” and “upper” or “top” may be used herein to describe the relationship between one element and another element as shown in the figures. It will be understood that, in addition to the orientations depicted in the figures, relative terms are also intended to include different orientations of the device. For example, if the device in one of the figures is flipped, the element described as being “on” the “lower” side of another element would be oriented on the “upper” side of said other element. Therefore, depending on the specific orientation of the figure, the exemplary term “lower” may include both “lower” and “upper” orientations.

[0036] As used herein, “about” or “approximately” includes the stated value and means within an acceptable range of deviations from the specific value, as determined by a person skilled in the art taking into account the measurement in question and the errors associated with the measurement of the specific quantity (i.e., limitations of the measurement system). For example, “about” may mean within one or more standard deviations relative to the stated value, or within ±5%.

[0037] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It will be further understood that terms, such as those defined in commonly used dictionaries, shall be interpreted as having a meaning consistent with their context in the relevant field and in this disclosure, and shall not be interpreted in an idealized or overly formal sense unless clearly defined herein.

[0038] In the accompanying drawings, the thicknesses of layers, films, panels, regions, etc., are enlarged for clarity. Throughout the specification, the same reference numerals denote the same elements. It will be understood that when an element, such as a layer, film, region, or substrate, is referred to as being "on" another element, it may be directly on said other element or there may be intermediate elements present. Conversely, when an element is referred to as being "directly on" another element, there are no intermediate elements present.

[0039] As used in this article, the term "combination" includes a mixture of two or more stacked structures or multiple components.

[0040] As used in this article, the term "metal" includes both metals and semi-metals.

[0041] The work function, highest occupied molecular orbital (HOMO) level, and lowest unoccupied molecular orbital (LUMO) level are represented as absolute values ​​relative to the vacuum level. Furthermore, when the work function, HOMO level, and LUMO level are referred to as "deep," "high," or "large," they have large absolute values ​​relative to the vacuum level of "0 eV," while when they are referred to as "shallow," "low," or "small," they have small absolute values ​​relative to the vacuum level of "0 eV."

[0042] The HOMO level was obtained by measuring the photoelectric work function of a thin film with a thickness of about 20 nm to about 30 nm using an AC-3 device (Riken Keiki Co. Ltd.), and by calculating the emission energy due to the photoelectron effect in the range of about 7.0 eV to about 4 eV for the energy of irradiation using the following formula.

[0043] E = h·c / λ

[0044] (h is Planck's constant, c is the speed of light, and λ is the wavelength)

[0045] The LUMO level can be measured by ultraviolet photoelectron spectroscopy (UPS).

[0046] A quantum dot light-emitting device according to an embodiment is described with reference to the following figures.

[0047] Figure 1 This is a schematic cross-sectional view of a quantum dot light-emitting device according to an embodiment, and Figure 2 for Figure 1 A schematic diagram of the energy levels of the quantum dot layer and the first and second electron transport layers of a quantum dot light-emitting device.

[0048] refer to Figure 1According to an embodiment, the quantum dot light-emitting device 10 includes: a first electrode 11 and a second electrode 12, each electrode having a surface opposite to the other; a quantum dot layer 13 between the first electrode 11 and the second electrode 12; a hole transport layer 14 between the first electrode 11 and the quantum dot layer 13; a first electron transport layer 15 and a second electron transport layer 16 disposed between the second electrode 12 and the quantum dot layer 13, wherein the second electron transport layer is disposed between the quantum dot layer 13 and the first electron transport layer 15, as shown.

[0049] A substrate (not shown) may be disposed on one side of the first electrode 11 or the second electrode 12. The substrate may be made, for example, of: inorganic materials such as glass; organic materials such as polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyethersulfone, or combinations thereof; or a silicon wafer. The substrate may be omitted.

[0050] One of the first electrode 11 and the second electrode 12 is an anode and the other is a cathode. For example, the first electrode 11 may be an anode and the second electrode 12 may be a cathode.

[0051] The first electrode 11 may be made of a conductor with a high work function, and may be made, for example, of a metal, a conductive metal oxide, or a combination thereof. The first electrode 11 may be made, for example, of a metal or an alloy thereof such as nickel, platinum, vanadium, chromium, copper, zinc, or gold; a conductive metal oxide such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine-doped tin oxide; or a combination of metal and oxide such as ZnO and Al or SnO2 and Sb, but is not limited thereto.

[0052] The second electrode 12 may be made of, for example, a conductor having a lower work function than the first electrode 11, and may be made of, for example, a metal, a conductive metal oxide, and / or a conductive polymer. The second electrode 12 may include, for example, metals or alloys thereof such as aluminum, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, silver, tin, lead, cesium, barium, etc.; multilayer structure materials such as LiF / Al, LiO2 / Al, Liq / Al, LiF / Ca, and BaF2 / Ca, but are not limited thereto.

[0053] The work function of the first electrode 11 may be higher than that of the second electrode 12. For example, the work function of the first electrode 11 may be from about 4.5 eV to about 5.0 eV, and the work function of the second electrode 12 may be from about 4.0 eV to about 4.7 eV, for example. Within the range described, the work function of the first electrode 11 may be from about 4.6 eV to about 4.9 eV, and the work function of the second electrode 12 may be from about 4.0 eV to about 4.5 eV, for example.

[0054] At least one of the first electrode 11 and the second electrode 12 may be a light-transmitting electrode, and the light-transmitting electrode may be made, for example, of a conductive oxide such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine-doped tin oxide, or a single or multiple metal thin layer. When one of the first electrode 11 and the second electrode 12 is a non-light-transmitting electrode, the non-light-transmitting electrode may be made of, for example, an opaque conductor such as aluminum (Al), silver (Ag), or gold (Au).

[0055] The quantum dot layer 13 comprises a plurality of quantum dots. These quantum dots may be semiconductor nanocrystals and may have various shapes, such as isotropic semiconductor nanocrystals, quantum rods, and quantum sheets. Here, a quantum rod may refer to a quantum dot having an aspect ratio greater than about 1:1, for example, greater than or equal to about 2:1, greater than or equal to about 3:1, or greater than or equal to about 5:1. For example, a quantum rod may have an aspect ratio less than or equal to about 50:1, less than or equal to about 30:1, or less than or equal to about 20:1.

[0056] The quantum dots may have an average particle diameter of, for example, about 1 nm to about 100 nm, about 1 nm to about 80 nm, about 1 nm to about 50 nm, or about 1 nm to about 20 nm (the size of the largest portion for non-spherical shapes).

[0057] The band gap of the quantum dot can be adjusted according to the particle size and composition of the quantum dot, and therefore, the photoluminescence wavelength of the quantum dot can be controlled. For example, when the particle size of the quantum dot increases, the quantum dot can have a narrower band gap and therefore emit light in a relatively long wavelength region. However, if the particle size of the quantum dot decreases, the quantum dot can have a wider band gap and therefore emit light in a relatively short wavelength region.

[0058] For example, the quantum dots may emit light, for example, in a predetermined wavelength region of the visible light region, depending on their particle size and / or chemical composition. For example, the quantum dots may emit blue light, red light, amber light, or green light. The blue light may have a peak emission wavelength in the range of, for example, from about 430 nanometers (nm) to about 480 nm; the red light may have a peak emission wavelength in the range of, for example, from about 600 nm to about 650 nm; the amber light may have a peak emission wavelength in the range of, for example, from about 570 nm to about 590 nm; and the green light may have a peak emission wavelength in the range of, for example, from about 520 nm to about 560 nm.

[0059] For example, the average particle size of the quantum dots emitting blue light may be, for example, less than or equal to about 4.5 nm, less than or equal to about 4.3 nm, less than or equal to about 4.2 nm, less than or equal to about 4.1 nm, or less than or equal to about 4.0 nm. Within the range, it may be, for example, about 2.0 nm to about 4.5 nm, about 2.0 nm to about 4.3 nm, about 2.0 nm to about 4.2 nm, about 2.0 nm to about 4.1 nm, or about 2.0 nm to about 4.0 nm.

[0060] The quantum dot may have a quantum yield of, for example, greater than or equal to about 10%, greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, or greater than or equal to about 90%.

[0061] The quantum dot may have a relatively narrow half-width (FWHM). In this paper, FWHM is the width of the wavelength corresponding to half of the peak absorption point, and the narrower the FWHM, the more light can be emitted in a narrower wavelength region and the higher the color purity can be obtained. The quantum dots may have a FWHM of, for example, less than or equal to about 50 nm, less than or equal to about 49 nm, less than or equal to about 48 nm, less than or equal to about 47 nm, less than or equal to about 46 nm, less than or equal to about 45 nm, less than or equal to about 44 nm, less than or equal to about 43 nm, less than or equal to about 42 nm, less than or equal to about 41 nm, less than or equal to about 40 nm, less than or equal to about 39 nm, less than or equal to about 38 nm, less than or equal to about 37 nm, less than or equal to about 36 nm, less than or equal to about 35 nm, less than or equal to about 34 nm, less than or equal to about 33 nm, less than or equal to about 32 nm, less than or equal to about 31 nm, less than or equal to about 30 nm, less than or equal to about 29 nm, or less than or equal to about 28 nm.

[0062] For example, the quantum dot may be, for example, a group II-VI semiconductor compound, a group III-V semiconductor compound, a group IV-VI semiconductor compound, a group IV semiconductor element or compound, a group I-III-VI semiconductor compound, a group I-II-IV-VI semiconductor compound, a group II-III-V semiconductor compound, or a combination thereof. The group II-VI semiconductor compound may be, for example, a binary compound such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or a combination thereof; or a ternary compound such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnSe, CdZnSe. nTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, or combinations thereof; and the following quaternary compounds: HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or combinations thereof, but not limited thereto. The III-V semiconductor compounds may be, for example, binary compounds such as GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or combinations thereof; ternary compounds such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, or combinations thereof; and quaternary compounds such as GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, InAlPSb, or combinations thereof, but are not limited thereto. The IV-VI semiconductor compounds may be, for example, binary compounds such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or combinations thereof; ternary compounds such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or combinations thereof; and quaternary compounds such as SnPbSSe, SnPbSeTe, SnPbSTe, or combinations thereof, but are not limited thereto.The group IV semiconductor elements or compounds may be, for example, elemental semiconductors such as Si, Ge, or combinations thereof; and binary semiconductor compounds such as SiC, SiGe, or combinations thereof, but are not limited thereto. The group I-III-VI semiconductor compounds may be, for example, CuInSe2, CuInS2, CuInGaSe, CuInGaS, or combinations thereof, but are not limited thereto. The group I-II-IV-VI semiconductor compounds may be, for example, CuZnSnSe, CuZnSnS, or combinations thereof, but are not limited thereto. The group II-III-V semiconductor compounds may include, for example, InZnP, but are not limited thereto.

[0063] The quantum dots may include elemental semiconductors, binary semiconductor compounds, ternary semiconductor compounds, or quaternary semiconductor compounds, distributed at substantially uniform or locally different concentrations.

[0064] For example, the quantum dots may include Cd-free quantum dots. Cadmium (Cd) causes serious environmental / health problems and is a restricted element under the Restriction of Hazardous Substances Directive (RoHS) in many countries, and therefore cadmium-free quantum dots can be used effectively.

[0065] For example, the quantum dot may be a semiconductor compound comprising at least one of zinc (Zn) and tellurium (Te) and selenium (Se). For example, the quantum dot may be a Zn-Te semiconductor compound, a Zn-Se semiconductor compound, and / or a Zn-Te-Se semiconductor compound. For example, in the Zn-Te-Se semiconductor compound, the amount of tellurium (Te) may be less than the amount of selenium (Se). The semiconductor compound may have a peak emission wavelength in a wavelength region less than or equal to about 480 nm, for example, in a wavelength region from about 430 nm to about 480 nm, and may emit blue light.

[0066] For example, the quantum dot may be a semiconductor compound comprising, for example, at least one of indium (In) and zinc (Zn) and phosphorus (P). For example, the quantum dot may be an In-P semiconductor compound and / or an In-Zn-P semiconductor compound. For example, in the In-Zn-P semiconductor compound, the molar ratio of zinc (Zn) to indium (In) may be greater than or equal to about 25:1. The semiconductor compound may have a peak emission wavelength in a wavelength region less than or equal to about 480 nm, for example, in a wavelength region from about 430 nm to about 480 nm, and may emit blue light.

[0067] The quantum dot may have a core-shell structure. For example, the core and shell of the quantum dot may have an interface, and at least one element of the core or the shell may have a concentration gradient at the interface, wherein the concentration of the element in the shell decreases toward the core. For example, the material composition of the shell of the quantum dot has a higher band gap than the material composition of the core of the quantum dot, and thereby the quantum dot may exhibit a quantum confinement effect.

[0068] The quantum dot may have a quantum dot core and a multilayer quantum dot shell surrounding the core. Here, the multilayer shell has at least two shells, wherein each shell may be a single composition, an alloy, and / or have a concentration gradient.

[0069] For example, the shells of a multilayered structure that are farther from the core may have a band gap that is close to the shell height of the core, and thus the quantum dot may exhibit a quantum confinement effect.

[0070] For example, a quantum dot having a core-shell structure may include a core and a shell, the core comprising a first semiconductor compound comprising at least one of zinc (Zn) and tellurium (Te) or selenium (Se), and the shell disposed on at least a portion of the surface of the core and comprising a second semiconductor compound having a composition different from that of the core.

[0071] For example, the first semiconductor compound may be a Zn-Te-Se based semiconductor compound comprising zinc (Zn), tellurium (Te), and selenium (Se), such as a Zn-Se based semiconductor compound comprising a relatively small amount of tellurium (Te), for example, a ZnTe x Se 1-x (where x is greater than about 0 and less than or equal to about 0.05) represents a semiconductor compound.

[0072] For example, in a first semiconductor compound based on Zn-Te-Se, the molar amount of zinc (Zn) may be greater than the molar amount of selenium (Se), and the molar amount of selenium (Se) may be greater than the molar amount of tellurium (Te). For example, in the first semiconductor compound, the molar ratio of tellurium (Te) to selenium (Se) may be less than or equal to about 0.05:1, less than or equal to about 0.049:1, less than or equal to about 0.048:1, less than or equal to about 0.047:1, less than or equal to about 0.045:1, less than or equal to about 0.044:1, less than or equal to about 0.043:1, less than or equal to about 0.042:1, less than or equal to about 0.041:1, less than or equal to about 0.04:1, less than or equal to about 0.039:1, less than or equal to about 0.035:1, less than or equal to about 0.03:1, less than or equal to about 0.029: 1. Less than or equal to about 0.025:1, less than or equal to about 0.024:1, less than or equal to about 0.023:1, less than or equal to about 0.022:1, less than or equal to about 0.021:1, less than or equal to about 0.02:1, less than or equal to about 0.019:1, less than or equal to about 0.018:1, less than or equal to about 0.017:1, less than or equal to about 0.016:1, less than or equal to about 0.015:1, less than or equal to about 0.014:1, less than or equal to about 0.013:1, less than or equal to about 0.012:1, less than or equal to about 0.011:1, or less than or equal to about 0.01:1. For example, in the first semiconductor compound, the molar ratio of tellurium (Te) to zinc (Zn) may be less than or equal to about 0.02:1, less than or equal to about 0.019:1, less than or equal to about 0.018:1, less than or equal to about 0.017:1, less than or equal to about 0.016:1, less than or equal to about 0.015:1, less than or equal to about 0.014:1, less than or equal to about 0.013:1, less than or equal to about 0.012:1, less than or equal to about 0.011:1, or less than or equal to about 0.010:1.

[0073] The second semiconductor compound may include, for example, group II-VI semiconductor compounds, group III-V semiconductor compounds, group IV-VI semiconductor compounds, group IV semiconductor elements or compounds, group I-III-VI semiconductor compounds, group I-II-IV-VI semiconductor compounds, group II-III-V semiconductor compounds, or combinations thereof. Examples of the group II-VI semiconductor compounds, group III-V semiconductor compounds, group IV-VI semiconductor compounds, group IV semiconductor elements or compounds, group I-III-VI semiconductor compounds, group I-II-IV-VI semiconductor compounds, and group II-III-V semiconductor compounds are the same as those described above.

[0074] For example, the second semiconductor compound may include zinc (Zn), and at least one of (Se) and sulfur (S). For example, the shell may include ZnSeS, ZnS, ZnSe, or combinations thereof. For example, the shell may include at least one inner shell disposed near the core and an outermost shell disposed at the outermost surface of the quantum dot, and the inner shell may include ZnSeS and the outermost shell may include ZnS. For example, the shell may have a concentration gradient of components, and for example, the amount of sulfur (S) may increase with distance from the core.

[0075] For example, a quantum dot having a core-shell structure may include, for example, a core and a shell, the core comprising a third semiconductor compound comprising at least one of indium (In) and zinc (Zn) and phosphorus (P), and the shell disposed on at least a portion of the core and comprising a fourth semiconductor compound having a composition different from that of the core.

[0076] In the In-Zn-P based third semiconductor compound, the molar ratio of zinc (Zn) to indium (In) can be greater than or equal to about 25:1. For example, in the In-Zn-P based third semiconductor compound, the molar ratio of zinc (Zn) to indium (In) can be greater than or equal to about 28:1, greater than or equal to about 29:1, or greater than or equal to about 30:1. For example, in the In-Zn-P based third semiconductor compound, the molar ratio of zinc (Zn) to indium (In) can be less than or equal to about 55:1, for example less than or equal to about 50:1, less than or equal to about 45:1, less than or equal to about 40:1, less than or equal to about 35:1, less than or equal to about 34:1, less than or equal to about 33:1, or less than or equal to about 32:1.

[0077] The fourth semiconductor compound may include, for example, group II-VI semiconductor compounds, group III-V semiconductor compounds, group IV-VI semiconductor compounds, group IV semiconductor elements or compounds, group I-III-VI semiconductor compounds, group I-II-IV-VI semiconductor compounds, group II-III-V semiconductor compounds, or combinations thereof. Examples of the group II-VI semiconductor compounds, group III-V semiconductor compounds, group IV-VI semiconductor compounds, group IV semiconductor elements or compounds, group I-III-VI semiconductor compounds, group I-II-IV-VI semiconductor compounds, and group II-III-V semiconductor compounds are the same as those described above.

[0078] For example, the fourth semiconductor compound may include zinc (Zn) and sulfur (S), and optionally selenium (Se). For example, the shell may include ZnSeS, ZnS, or a combination thereof. For example, the shell may include at least one inner shell disposed near the core and an outermost shell disposed at the outermost surface of the quantum dot, and at least one of the inner shell and the outermost shell may include a fourth semiconductor compound of ZnS or ZnSeS.

[0079] The quantum dot layer 13 may have a thickness of, for example, about 5 nm to about 200 nm, for example, about 10 nm to about 150 nm, about 10 nm to about 100 nm, or about 10 nm to about 50 nm.

[0080] The quantum dot layer 13 may have relatively deep HOMO levels and may have HOMO levels greater than or equal to about 5.4 eV, greater than or equal to about 5.6 eV, greater than or equal to about 5.7 eV, greater than or equal to about 5.8 eV, greater than or equal to about 5.9 eV, or greater than or equal to about 6.0 eV. The HOMO energy levels of quantum dot layer 13 may be, for example, about 5.4 eV to about 7.0 eV, about 5.4 eV to about 6.8 eV, about 5.4 eV to about 6.7 eV, about 5.4 eV to about 6.5 eV, about 5.4 eV to about 6.3 eV, about 5.4 eV to about 6.2 eV, or about 5.4 eV to about 6.1 eV, or within the range of, for example, about 5.6 eV to about 7.0 eV, about 5.6 eV to about 6.8 eV, about 5.6 eV to about 6.7 eV, about 5.6 eV to about 6.5 eV, about 5.6 eV to about 6.3 eV, about 5.6 eV to about 6.2 eV, or about 5.6 eV to about 6.1 eV, for example, about 5.7 eV to about 7.0 eV, about 5.7 eV to about 6.8 eV, or about 5. 0.7eV to about 6.7eV, about 5.7eV to about 6.5eV, about 5.7eV to about 6.3eV, about 5.7eV to about 6.2eV, or about 5.7eV to about 6.1eV, for example about 5.8eV to about 7.0eV, about 5.8eV to about 6.8eV, about 5.8eV to about 6.7eV, about 5.8eV to about 6.5eV, about 5.8eV to about 6.3eV, about 5.8eV to about 6.2eV, about 5.8eV to about 6.1eV, for example about 6.0eV to about 7.0eV, about 6.0eV to about 6.8eV, about 6.0eV to about 6.7eV, about 6.0eV to about 6.5eV, about 6.0eV to about 6.3eV, or about 6.0eV to about 6.2eV.

[0081] The quantum dot layer 13 may have relatively shallow LUMO energy levels and may have LUMO energy levels of, for example, less than or equal to about 3.6 eV, less than or equal to about 3.5 eV, less than or equal to about 3.4 eV, less than or equal to about 3.3 eV, less than or equal to about 3.2 eV, or less than or equal to about 3.0 eV. The LUMO energy levels of the quantum dot layer 13 may be, for example, about 2.5 eV to about 3.6 eV, about 2.5 eV to about 3.5 eV, about 2.5 eV to about 3.4 eV, about 2.5 eV to about 3.3 eV, about 2.5 eV to about 3.2 eV, about 2.5 eV to about 3.1 eV, about 2.5 eV to about 3.0 eV, about 2.8 eV to about 3.6 eV, about 2.8 eV to about 3.5 eV, about 2.8 eV to about 3.4 eV, about 2.8 eV to about 3.3 eV, about 2.8 eV to about 3.2 eV, about 3.0 eV to about 3.6 eV, about 3.0 eV to about 3.5 eV, or about 3.0 eV to about 3.4 eV.

[0082] The quantum dot layer 13 may have a band gap of about 2.4 eV to about 2.9 eV. Within the range, the quantum dot layer 13 may have a band gap of, for example, about 2.4 eV to about 2.8 eV, or, for example, about 2.4 eV to about 2.78 eV.

[0083] A hole transport layer 14 is disposed between the first electrode 11 and the quantum dot layer 13. The hole transport layer 14 may have one layer or two or more layers. In a broader sense, in addition to the hole transport layer, the hole transport layer 14 may also include a hole injection layer and / or an electron blocking layer.

[0084] The hole transport layer 14 can have a relatively deep HOMO level, allowing it to match the HOMO level of the quantum dot layer 13. Therefore, the mobility of holes from the hole transport layer 14 to the quantum dot layer 13 can be increased.

[0085] The HOMO energy level of the hole transport layer 14 may be equal to or smaller than the HOMO energy level of the quantum dot layer 13, for example, in the range of about 1.0 eV or less. For example, the difference between the HOMO energy levels of the hole transport layer 14 and the quantum dot layer 13 may be about 0 eV to about 1.0 eV, for example, about 0.01 eV to about 0.8 eV, about 0.01 eV to about 0.7 eV, about 0.01 eV to about 0.5 eV, about 0.01 eV to about 0.4 eV, about 0.01 eV to about 0.3 eV, about 0.01 eV to about 0.2 eV, or about 0.01 eV to about 0.1 eV.

[0086] The HOMO level of hole transport layer 14 may be, for example, greater than or equal to about 5.0 eV, greater than or equal to about 5.2 eV, greater than or equal to about 5.4 eV, greater than or equal to about 5.6 eV, or greater than or equal to about 5.8 eV.

[0087] For example, the HOMO energy levels of the hole transport layer 14 can be approximately 5.0 eV to approximately 7.0 eV, approximately 5.2 eV to approximately 6.8 eV, approximately 5.4 eV to approximately 6.8 eV, approximately 5.4 eV to approximately 6.7 eV, approximately 5.4 eV to approximately 6.5 eV, approximately 5.4 eV to approximately 6.3 eV, approximately 5.4 eV to approximately 6.2 eV, approximately 5.4 eV to approximately 6.1 eV, approximately 5.6 eV to approximately 7.0 eV, approximately 5.6 eV to approximately 6.8 eV, and approximately 5.6 eV to approximately 7.0 eV. V to about 6.7 eV, about 5.6 eV to about 6.5 eV, about 5.6 eV to about 6.3 eV, about 5.6 eV to about 6.2 eV, about 5.6 eV to about 6.1 eV, about 5.8 eV to about 7.0 eV, about 5.8 eV to about 6.8 eV, about 5.8 eV to about 6.7 eV, about 5.8 eV to about 6.5 eV, about 5.8 eV to about 6.3 eV, about 5.8 eV to about 6.2 eV, or about 5.8 eV to about 6.1 eV.

[0088] The hole transport layer 14 may comprise any material that satisfies the energy level without particular limitation, and may be at least one of the following: poly(9,9-dioctylfluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), polyarylamines (polyarylamines), poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene):polysulfonated styrene (PEDOT:PSS), polyaniline, polypyrrole, N,N,N',N'-tetra(4-methoxyphenyl)-biphenyl Amines (TPD), 4,4'-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA (4,4',4”-tris[phenyl(m-tolyl)amino]triphenylamine), 4,4',4”-tris(N-carbazolyl)triphenylamine (TCTA), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), p-type metal oxides (e.g., NiO, WO3, MoO3, etc.), carbon-based materials such as graphene oxides, and combinations thereof, but not limited thereto.

[0089] The first electron transport layer 15 and the second electron transport layer 16 are disposed between the second electrode 12 and the quantum dot layer 13. The first electron transport layer 15 is disposed close to the second electrode 12, and the second electron transport layer 16 is disposed close to the quantum dot layer 13. That is, the second electron transport layer 16 is disposed between the quantum dot layer 13 and the first electron transport layer 15. Therefore, the second electrode 12, the first electron transport layer 15, the second electron transport layer 16, and the quantum dot layer 13 can be disposed sequentially adjacent to each other.

[0090] For example, the first electron transport layer 15 may be in contact with the second electrode 12, and the second electron transport layer 16 may be in contact with the quantum dot layer 13.

[0091] For example, the first electron transport layer 15 and the second electron transport layer 16 can be in contact with each other.

[0092] For example, one surface of the first electron transport layer 15 may be in contact with the second electrode 12, and the other surface of the first electron transport layer 15 may be in contact with the second electron transport layer 16.

[0093] For example, one surface of the second electron transport layer 16 may be in contact with the quantum dot layer 13, and the other surface of the second electron transport layer 16 may be in contact with the first electron transport layer 15.

[0094] refer to Figure 2 The LUMO levels of the first electron transport layer 15, the second electron transport layer 16, and the quantum dot layer 13 are progressively shallower in this order. For example, the LUMO level of the second electron transport layer 16 (LUMO 16 The LUMO energy level of the first electron transport layer 15 (LUMO) 15 The LUMO level of quantum dot layer 13 is shallow and has low LUMO energy. 13 The LUMO level of the second electron transport layer is comparable to that of the second electron transport layer. 16 Shallow. That is, the LUMO level of the first electron transport layer 15 (LUMO 15 ), the LUMO level of the second electron transport layer 16 (LUMO 16 ), and the LUMO level of quantum dot layer 13 (LUMO 13 It can have a series of energy levels that gradually become shallower in the direction from the first electron transport layer 15 to the quantum dot layer 13.

[0095] For example, the LUMO levels of the first electron transport layer 15, the second electron transport layer 16, and the quantum dot layer 13 can be stepped. Relatively small energy barriers (d1 and d2) can exist between the first electron transport layer 15 and the second electron transport layer 16, and between the second electron transport layer 16 and the quantum dot layer 13. The energy barrier (d1) between the first electron transport layer 15 and the second electron transport layer 16 can be the LUMO level of the first electron transport layer 15 (LUMO). 15 ) and the LUMO level of the second electron transport layer 16 (LUMO 16 The difference between ) and ). The energy barrier (d2) between the second electron transport layer 16 and the quantum dot layer 13 can be the LUMO level (LUMO) of the second electron transport layer 16. 16 ) and the LUMO level of quantum dot layer 13 (LUMO 13 The difference between them.

[0096] For example, the energy barrier (d1) between the first electron transport layer 15 and the second electron transport layer 16, i.e., the LUMO level (LUMO) of the first electron transport layer 15. 15 ) and the LUMO level of the second electron transport layer 16 (LUMO 16 The difference between them can be about 0.01 eV to about 1.20 eV, about 0.01 eV to about 1.15 eV, about 0.01 eV to 1.10 eV, about 0.01 eV to about 1.05 eV, about 0.01 eV to about 1.00 eV, about 0.01 eV to about 0.80 eV, about 0.01 eV to about 0.70 eV, about 0.01 eV to about 0.50 eV, about 0.01 eV to about 0.40 eV, about 0.01 eV to about 0.30 eV, or about 0.01 eV to about 0.20 eV.

[0097] For example, the energy barrier (d2) between the second electron transport layer 16 and the quantum dot layer 13, i.e., the LUMO level (LUMO) of the second electron transport layer 16. 16 ) and the LUMO level of quantum dot layer 13 (LUMO 13 The difference between them can be from about 0.01 eV to about 1.20 eV, for example, from about 0.01 eV to about 1.00 eV, from about 0.01 eV to about 0.80 eV, from about 0.01 eV to about 0.70 eV, from about 0.01 eV to about 0.50 eV, from about 0.01 eV to about 0.40 eV, from about 0.01 eV to about 0.30 eV, or from about 0.01 eV to about 0.20 eV.

[0098] For example, the energy barrier (d1) between the first electron transport layer 15 and the second electron transport layer 16, i.e., the LUMO level (LUMO) of the first electron transport layer 15. 15) and the LUMO level of the second electron transport layer 16 (LUMO 16 The difference between the two can be less than the energy barrier (d2) between the second electron transport layer 16 and the quantum dot layer 13, that is, at the LUMO level (LUMO) of the second electron transport layer 16. 16 ) and the LUMO level of quantum dot layer 13 (LUMO 13 The difference between them.

[0099] For example, the energy barrier (d1) between the first electron transport layer 15 and the second electron transport layer 16, i.e., the LUMO level (LUMO) of the first electron transport layer 15. 15 ) and the LUMO level of the second electron transport layer 16 (LUMO 16 The difference between the two can be approximately 0.01 eV to approximately 1.00 eV, approximately 0.01 eV to approximately 0.80 eV, approximately 0.01 eV to approximately 0.70 eV, approximately 0.01 eV to approximately 0.50 eV, approximately 0.01 eV to approximately 0.40 eV, approximately 0.01 eV to approximately 0.30 eV, or approximately 0.01 eV to approximately 0.20 eV, and the energy barrier (d2) between the second electron transport layer 16 and the quantum dot layer 13, i.e., the LUMO level (LUMO) of the second electron transport layer 16. 16 ) and the LUMO level of quantum dot layer 13 (LUMO 13 The difference between them can be from about 0.50 eV to about 1.20 eV, and can be, for example, from about 0.60 eV to about 1.20 eV, from about 0.70 eV to about 1.20 eV, from about 0.80 eV to about 1.20 eV, from about 0.90 eV to about 1.20 eV, or from about 1.00 eV to about 1.20 eV.

[0100] For example, the LUMO level (LUMO) of quantum dot layer 13 13 The LUMO energy levels of quantum dot layer 13 can be, for example, less than or equal to about 3.6 eV, less than or equal to about 3.5 eV, less than or equal to about 3.4 eV, less than or equal to about 3.3 eV, less than or equal to about 3.2 eV, or less than or equal to about 3.0 eV. Within these ranges, the LUMO energy levels of quantum dot layer 13... 13The values ​​can be, for example, about 2.5 eV to about 3.6 eV, about 2.5 eV to about 3.5 eV, for example, about 2.5 eV to about 3.4 eV, for example, about 2.5 eV to about 3.3 eV, for example, about 2.5 eV to about 3.2 eV, for example, about 2.5 eV to about 3.1 eV, for example, about 2.5 eV to about 3.0 eV, for example, about 2.8 eV to about 3.6 eV, about 2.8 eV to about 3.5 eV, about 2.8 eV to about 3.4 eV, about 2.8 eV to about 3.3 eV, about 2.8 eV to about 3.2 eV, about 3.0 eV to about 3.6 eV, about 3.0 eV to about 3.5 eV, or about 3.0 eV to about 3.4 eV.

[0101] For example, the LUMO level of the first electron transport layer 15 (LUMO 15 The voltage range can be, for example, less than or equal to about 4.8 eV, less than or equal to about 4.6 eV, about 3.2 eV to about 4.8 eV, about 3.2 eV to about 4.6 eV, about 3.2 eV to about 4.5 eV, about 3.2 eV to about 4.3 eV, about 3.2 eV to about 4.1 eV, about 3.4 eV to 4.1 eV, about 3.6 eV to about 4.1 eV, about 3.5 eV to about 4.6 eV, about 3.8 eV to about 4.6 eV, or about 4.1 eV to about 4.6 eV.

[0102] For example, the LUMO level of the second electron transport layer 16 (LUMO 16 This can be used for the LUMO energy level in quantum dot layer 13 (LUMO). 13 ) and the LUMO level of the first electron transport layer 15 (LUMO 15 The values ​​between ) . For example, the LUMO level (LUMO) of the second electron transport layer 16. 16 The voltage can be less than or equal to about 4.2 eV, about 2.8 eV to about 4.2 eV, about 2.8 eV to about 4.1 eV within the range, about 3.0 eV to about 4.1 eV, about 3.2 eV to 4.1 eV, about 3.4 eV to about 4.1 eV, about 2.8 eV to about 4.0 eV, about 3.0 eV to about 4.0 eV, about 3.2 eV to 4.0 eV, about 3.4 eV to about 4.0 eV, about 3.5 eV to about 4.2 eV, about 3.5 eV to about 4.1 eV, or about 3.5 eV to about 4.0 eV.

[0103] The first electron transport layer 15, the second electron transport layer 16, and the quantum dot layer 13 satisfy the aforementioned relationship at the LUMO energy level, thereby reducing the energy barrier caused by the large LUMO energy level difference between the first electron transport layer 15 and the quantum dot layer 13 and promoting electron injection and transport, thus improving the efficiency of the quantum dot light-emitting device. Unlike cadmium-based quantum dot layers that emit blue light and / or quantum dot layers that emit red and green light, such a structure can be effectively applied to quantum dot light-emitting devices that include a Cd-free quantum dot layer 13 emitting blue light with a relatively large band gap and shallow LUMO energy level.

[0104] For example, the LUMO level of the first electron transport layer 15 may be deeper than the work function or LUMO level of the second electrode 12. For example, the LUMO level of the first electron transport layer 15 may be shallower than the work function or LUMO level of the second electrode 12. For example, the LUMO level of the first electron transport layer 15 may be substantially equal to the work function or LUMO level of the second electrode 12.

[0105] The first electron transport layer 15 may include inorganic materials that satisfy the aforementioned energy levels. The first electron transport layer 15 may include, for example, inorganic nanoparticles, oxide nanoparticles, and metal oxide nanoparticles.

[0106] The nanoparticles included in the first electron transport layer 15 may be two-dimensional or three-dimensional particles having an average particle diameter in the range of about 10 nm, about 8 nm, about 7 nm, about 5 nm, about 4 nm, or about 3.5 nm, or in the range of about 1 nm to about 10 nm, about 1 nm to about 9 nm, about 1 nm to about 8 nm, about 1 nm to about 7 nm, about 1 nm to about 5 nm, about 1 nm to about 4 nm, or about 1 nm to about 3.5 nm.

[0107] For example, the first electron transport layer 15 may include first metal oxide nanoparticles, and the first metal oxide nanoparticles may include at least one of the following: zinc (Zn), magnesium (Mg), cobalt (Co), nickel (Ni), gallium (Ga), aluminum (Al), calcium (Ca), zirconium (Zr), tungsten (W), lithium (Li), titanium (Ti), tantalum (Ta), tin (Sn), hafnium (Hf), and barium (Ba).

[0108] For example, the first electron transport layer 15 may include metal oxide nanoparticles containing zinc (Zn), and may include those made of Zn. 1-x Q xO (0≤x<0.5) represents metal oxide nanoparticles. Here, Q is a metal element other than Zn, such as magnesium (Mg), cobalt (Co), nickel (Ni), gallium (Ga), aluminum (Al), calcium (Ca), zirconium (Zr), tungsten (W), lithium (Li), titanium (Ti), tantalum (Ta), tin (Sn), hafnium (Hf), silicon (Si), barium (Ba), or combinations thereof.

[0109] For example, Q can be magnesium (Mg).

[0110] For example, x can be in the range of 0.01≤x≤0.3, such as 0.01≤x≤0.2 or 0.01≤x≤0.1.

[0111] The first electron transport layer 15 may have a thickness in the range of about 2 nm to about 80 nm, about 2 nm to about 70 nm, about 2 nm to about 60 nm, about 2 nm to about 50 nm, about 2 nm to about 40 nm, or about 2 nm to about 30 nm.

[0112] The second electron transport layer 16 may include an inorganic material that satisfies the aforementioned energy levels between the quantum dot layer 13 and the first electron transport layer 15. The inorganic material included in the second electron transport layer 16 may be different from the inorganic material included in the first electron transport layer 15.

[0113] For example, the second electron transport layer 16 may include oxides, such as metal oxides, or metal oxide semiconductors. However, when the metal oxide or metal oxide semiconductor included in the first electron transport layer 15 includes zinc, the metal oxide or metal oxide semiconductor included in the second electron transport layer 16 may not include zinc.

[0114] For example, the second electron transport layer 16 may include cerium-containing oxides (hereinafter referred to as "cerium oxides"), strontium-titanium-containing oxides (hereinafter referred to as "strontium-titanium oxides"), niobium-containing oxides (hereinafter referred to as "niobium oxides"), barium-tin-containing oxides (hereinafter referred to as "barium-tin oxides"), or combinations thereof.

[0115] The cerium oxide may be, for example, made from Ce. 1-z A z O (0≤z<0.5), Ce 1-z A z O2 (0≤z<0.5), Ce 2-z A z O3 (0≤z<1), and / or Ce 3-z A zO4 (0≤z<1.5) represents a metal element other than Ce, such as Zn, Mg, Co, Cu, Eu, Gd, Sm, Ni, Al, Mn, Pt, Sn, La, Al, Fe, and / or Y, but not limited thereto. For example, the cerium oxide may be, for example, CeO, CeO2, Ce2O3, Ce3O4, or a combination thereof. The strontium titanium oxide may be, for example, SrTiO3, the niobium oxide may be Nb2O5, and the barium tin oxide may be BaSnO3, but they are not limited thereto.

[0116] For example, the second electron transport layer 16 may include inorganic nanoparticles, such as oxide nanoparticles, and for example, metal oxide nanoparticles. The metal oxide nanoparticles may be crystalline nanoparticles with high thermochemical stability and may be inorganic semiconductors with a relatively wide band gap, for example, from about 3.0 eV to about 6.0 eV. However, when the metal oxide nanoparticles included in the first electron transport layer 15 include zinc, the metal oxide nanoparticles included in the second electron transport layer 16 may not include zinc.

[0117] The inorganic nanoparticles included in the second electron transport layer 16 may be two-dimensional or three-dimensional particles having an average particle diameter in the range of about 10 nm, about 8 nm, about 7 nm, about 5 nm, about 4 nm, or about 3.5 nm, or about 1 nm to about 10 nm, about 1 nm to about 9 nm, about 1 nm to about 8 nm, about 1 nm to about 7 nm, about 1 nm to about 5 nm, about 1 nm to about 4 nm, or about 1 nm to about 3.5 nm.

[0118] For example, the second electron transport layer 16 may include second metal oxide nanoparticles that are different from the aforementioned first metal oxide nanoparticles. The second metal oxide nanoparticles may include, for example, cerium oxide nanoparticles, strontium titanium oxide nanoparticles, niobium oxide nanoparticles, barium tin oxide nanoparticles, or combinations thereof.

[0119] In addition to the aforementioned inorganic materials, the second electron transport layer 16 may further include an n-type dopant. The n-type dopant included in the second electron transport layer 16 can increase the electron density, further improve electron mobility, and provide a reduction in the turn-on voltage.

[0120] The n-type dopant may include metal elements, metal compounds, metal salts, or combinations thereof, such as metal compounds or metal salts of cesium (Cs), rubidium (Rb), lithium (Li), sodium (Na), potassium (K), tin (Sn), nickel (Ni), cobalt (Co), molybdenum (Mo), vanadium (V), gallium (Ga), manganese (Mn), iron (Fe), niobium (Nb), strontium (Sr), barium (Ba), indium (In), calcium (Ca), zirconium (Zr), tungsten (W), titanium (Ti), yttrium (Y), aluminum (Al), or combinations thereof, such as cesium (Cs), rubidium (Rb), lithium (Li), sodium (Na), potassium (K), cesium carbonate (Cs₂CO₃), cesium phosphate (Cs₃PO₄), cesium vanadate (Cs₃VO₄), cesium azide (CsN₃), lithium nitride (Li₃N), rubidium carbonate (Rb₂CO₃), or metal salts derived therefrom, but not limited thereto.

[0121] Based on the total volume of the second electron transport layer 16, the n-type dopant may be included in the second electron transport layer in the following amounts: less than about 50 vol%, or greater than or equal to about 0.01 vol% and less than about 50 vol%, about 0.01 vol% to about 40 vol%, about 0.1 vol% to about 40 vol%, about 1 vol% to about 40 vol%, about 3 vol% to about 40 vol%, about 5 vol% to about 40 vol%, about 5 vol% to about 35 vol%, about 5 vol% to about 30 vol%, about 5 vol% to about 28 vol%, about 5 vol% to about 25 vol%, about 5 vol% to about 20 vol%, or about 5 vol% to about 15 vol%, but not limited thereto.

[0122] The amount of metal atoms included as the n-type dopant may be smaller than that of the dominant metal atoms (i.e., the metal atoms included in the metal oxide nanoparticles), both of which are included in the second electron transport layer 16. For example, based on the total number of metal atoms corresponding to the metal oxide nanoparticles and the n-type dopant in the second electron transport layer 16, the amount of metal atoms included as the n-type dopant may be present in the following amounts: less than about 50 atomic percentages (atomic %), or greater than or equal to about 0.01 atomic % and less than about 50 atomic %, greater than or equal to about 0.05 atomic % and less than about 50 atomic %, about 0.01 atomic % to about 40 atomic %, about 0.1 atomic % to about 40 atomic %, about 1 atomic % to about 40 atomic %, about 2 atomic % to about 40 atomic %, about 3 atomic % to about 40 atomic %, about 4 atomic % to about 40 atomic %, about 2 ... The range of about 35 atomic percent, about 4 atomic percent to about 35 atomic percent, about 2 atomic percent to about 35 atomic percent, about 2 atomic percent to about 30 atomic percent, about 4 atomic percent to about 30 atomic percent, about 2 atomic percent to about 28 atomic percent, about 4 atomic percent to about 28 atomic percent, about 2 atomic percent to about 25 atomic percent, about 4 atomic percent to about 25 atomic percent, about 2 atomic percent to about 23 atomic percent, about 4 atomic percent to about 23 atomic percent, about 2 atomic percent to about 20 atomic percent, about 4 atomic percent to about 20 atomic percent, about 2 atomic percent to about 18 atomic percent, about 4 atomic percent to about 18 atomic percent, about 2 atomic percent to about 16 atomic percent, or about 4 atomic percent to about 16 atomic percent, but not limited thereto.

[0123] For example, when the second electron transport layer 16 comprises cerium oxide as the metal oxide nanoparticles and cesium salt as the n-type dopant, based on the total number of cerium and cesium atoms, cesium may be included in the following amounts: less than about 50 atomic percent, or greater than or equal to about 0.01 atomic percent and less than about 50 atomic percent, greater than or equal to about 0.1 atomic percent and less than about 50 atomic percent, about 0.01 atomic percent to about 40 atomic percent, about 0.1 atomic percent to about 40 atomic percent, about 1 atomic percent to about 40 atomic percent. The range of approximately 3 atomic percent to approximately 40 atomic percent, approximately 3 atomic percent to approximately 30 atomic percent, approximately 3 atomic percent to approximately 25 atomic percent, approximately 3 atomic percent to approximately 20 atomic percent, approximately 3 atomic percent to approximately 16 atomic percent, approximately 5 atomic percent to approximately 40 atomic percent, approximately 5 atomic percent to approximately 35 atomic percent, approximately 5 atomic percent to approximately 30 atomic percent, approximately 5 atomic percent to approximately 28 atomic percent, approximately 5 atomic percent to approximately 25 atomic percent, approximately 5 atomic percent to approximately 20 atomic percent, and approximately 5 atomic percent to approximately 16 atomic percent, but not limited thereto.

[0124] For example, the first electron transport layer 15 and the second electron transport layer 16 may each comprise metal oxide nanoparticles, and each may comprise metal oxide nanoparticles having an average particle diameter of less than or equal to about 10 nm, less than or equal to about 7 nm, or less than or equal to about 5 nm. For example, the first electron transport layer 15 may comprise Zn as described above. 1-x Q x O (where Q is Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Si, Ba, or a combination thereof, and 0 ≤ x < 0.5), and the second electron transport layer 16 may include the aforementioned cerium oxide nanoparticles and optionally further include the n-type dopants described above.

[0125] In another embodiment, we describe a layered structure that includes

[0126] Quantum dot layer,

[0127] A first electron transport layer and a second electron transport layer are disposed on the quantum dot layer, wherein the second electron transport layer is disposed between the quantum dot layer and the first electron transport layer, and each of the first electron transport layer and the second electron transport layer comprises an inorganic material.

[0128] The LUMO level of the second electron transport layer is shallower than the LUMO level of the first electron transport layer.

[0129] The LUMO energy level of the quantum dot layer is shallower than the LUMO energy level of the second electron transport layer, and the layered structure is disposed between the first electrode and the second electrode.

[0130] Furthermore, the layered structure can be designed to have a LUMO energy level difference of about 0.01 eV to about 0.50 eV between the LUMO energy levels of the first electron transport layer and the second electron transport layer, and a LUMO energy level difference of about 0.01 eV to about 1.20 eV between the LUMO energy levels of the second electron transport layer and the quantum dot layer. Additionally, the LUMO energy level of the first electron transport layer is about 3.2 eV to about 4.8 eV, the LUMO energy level of the second electron transport layer is about 2.8 eV to about 4.2 eV, and the LUMO energy level of the quantum dot layer is about 2.5 eV to about 3.6 eV.

[0131] In one embodiment, the second electron transport layer of the layered structure may include cerium oxide nanoparticles, strontium titanium oxide nanoparticles, niobium oxide nanoparticles, barium tin oxide nanoparticles, or combinations thereof, and an n-type dopant, wherein the n-type dopant includes alkali metals, Sn, Ni, Co, Mo, V, Ga, Mn, Fe, Nb, Sr, Ba, In, Ca, Zr, W, Ti, Y, Al, or combinations thereof.

[0132] In another embodiment, the second electron transport layer of the layered structure may include cerium oxide nanoparticles and cesium, cesium oxide, or a combination thereof, wherein cesium is present in an amount of 3 atomic percent to 16 atomic percent based on the total number of cerium and cesium atoms, and the first electron transport layer includes zinc oxide nanoparticles.

[0133] In one embodiment, the quantum dot layer of the layered structure comprises cadmium-free quantum dots, and the quantum dot layer emits light having a peak emission wavelength region of about 430 nm to about 480 nm.

[0134] The second electron transport layer 16 may have a thickness in the range of about 2 nm to about 80 nm, or about 2 nm to about 70 nm, about 2 nm to about 60 nm, about 2 nm to about 50 nm, about 2 nm to about 40 nm, or about 2 nm to about 30 nm.

[0135] For example, the second electron transport layer 16 may have a smaller thickness than the first electron transport layer 15. For example, the thickness of the second electron transport layer 16 may be about 0.1 to about 0.8 times, about 0.1 to about 0.7 times, or about 0.1 to about 0.5 times the thickness of the first electron transport layer 15, but is not limited thereto.

[0136] The aforementioned quantum dot layer 13 and the first and second electron transport layers 15 and 16 may be formed, for example, by solution processing or deposition processing, and the solution processing may be, for example, spin coating, slot coating, inkjet printing, nozzle printing, jetting and / or blade coating, but is not limited thereto.

[0137] Depending on the emission wavelength spectrum of the quantum dot layer 13, the quantum dot light-emitting device 10 can display blue, green, or red. For example, the quantum dot light-emitting device 10 can display blue through the quantum dot layer 13 to emit light with a blue wavelength spectrum having a peak emission wavelength in the range of about 430 nm to about 480 nm. For example, the quantum dot light-emitting device 10 can display green through the quantum dot layer 13 to emit light with a green wavelength spectrum having a peak emission wavelength in the range of about 520 nm to about 560 nm. Or, for example, the quantum dot light-emitting device 10 can display red through the quantum dot layer 13 to emit light with a red wavelength spectrum having a peak emission wavelength in the range of about 600 nm to about 650 nm.

[0138] The quantum dot light-emitting device 10 may have improved electrical and luminescent properties. For example, the external quantum efficiency (EQE) of the quantum dot light-emitting device 10 may be equal to or greater than about 6.0%, equal to or greater than about 7.0%, equal to or greater than about 8.0%, equal to or greater than about 9.0%, or equal to or greater than about 10.0%.

[0139] In addition, the quantum dot light-emitting device 10 may have an ampere strength equal to or greater than approximately 180 A / cm². 2 ), equal to or greater than approximately 190 A / cm 2 Equal to or greater than approximately 200 A / cm 2 Equal to or greater than approximately 220 A / cm 2 Equal to or greater than approximately 240 A / cm 2 Equal to or greater than approximately 250 A / cm 2 Equal to or greater than approximately 270 A / cm 2 Equal to or greater than approximately 280 A / cm 2 Equal to or greater than approximately 300 A / cm 2 Equal to or greater than approximately 310 A / cm 2 Equal to or greater than approximately 320 A / cm 2 Or equal to or greater than approximately 330 A / cm 2 The current density.

[0140] Furthermore, the quantum dot light-emitting device 10 may have a driving voltage equal to or less than about 4.2V, equal to or less than about 4.1V, equal to or less than about 4.0V, equal to or less than about 3.9V, equal to or less than about 3.8V, equal to or less than about 3.7V, equal to or less than about 3.6V, or equal to or less than about 3.5V, and the current efficiency of the quantum dot light-emitting device 10 may be equal to or greater than about 5.0 candela / ampere (maximum) (Cd / A). max ), equal to or greater than approximately 5.2 Cd / A max Equal to or greater than approximately 5.4 Cd / A max Equal to or greater than approximately 5.6 Cd / A max Equal to or greater than approximately 5.8 Cd / A max Equal to or greater than approximately 6.0 Cd / A max Or equal to or greater than approximately 6.2 Cd / A max Furthermore, the luminous efficiency of the quantum dot light-emitting device 10 (at 5 mA) can be equal to or greater than approximately 100 candela per square meter (Cd / m²). 2 ), equal to or greater than approximately 120 Cd / m 2 Equal to or greater than approximately 140 Cd / m 2 Equal to or greater than approximately 150 Cd / m 2Equal to or greater than approximately 160 Cd / m 2 Equal to or greater than approximately 170 Cd / m 2 Equal to or greater than approximately 180 Cd / m 2 Equal to or greater than approximately 190 Cd / m 2 Equal to or greater than approximately 200 Cd / m 2 Or equal to or greater than approximately 210 Cd / m³ 2 .

[0141] The quantum dot light-emitting device 10 can be applied to a variety of electronic devices that require light emission, such as display devices or lighting devices.

[0142] The embodiments are described in more detail below with reference to examples. However, these embodiments are exemplary and the scope is not limited thereto.

[0143] Synthesis of quantum dot dispersions

[0144] Synthesis Example 1

[0145] (1) Synthesis of ZnTeSe core quantum dot dispersion

[0146] Selenium (Se) and tellurium (Te) were dispersed in trioctylphosphine (TOP) to obtain 2M Se / TOP stock solutions and 0.1M Te / TOP stock solutions. 0.125 mmol zinc acetate, 0.25 mmol oleic acid, and 0.25 mmol hexadecylamine were combined with 10 mL trioctylamine in a reactor and heated under vacuum at 120 °C. After 1 hour, nitrogen was added to the reactor. The reactor was then heated to 240 °C, and the Se / TOP and Te / TOP stock solutions were rapidly added to the reactor at a Te / Se molar ratio of 1 / 25 (reaction mixture). After increasing the temperature to 300 °C and maintaining the reaction mixture at 300 °C for 30 minutes, the reaction mixture was rapidly cooled to room temperature, and acetone was added to the reaction mixture. A precipitate was obtained and separated by centrifugation. The resulting precipitate was dispersed in toluene to obtain a ZnTeSe core quantum dot dispersion.

[0147] (2) Synthesis of ZnTeSe core / ZnSeS shell quantum dot dispersions

[0148] Trioctylamine was added to a 10 mL reaction flask, along with 0.6 mmol of zinc acetate and 1.2 mmol of oleic acid. The flask was placed under vacuum and the temperature was raised to 120 °C over 10 minutes. Nitrogen (N2) was then added to the flask, and the ZnTeSe core quantum dot dispersion obtained in step (1) above was rapidly injected into the reaction flask. A dispersion of 2 M Se / TOP and 1 M S / TOP was added to the reaction mixture to obtain a Se:S molar ratio of 1.2:2.8. The reaction temperature was raised to 340 °C and maintained until the reaction was complete. The reaction flask (reaction product) was cooled to room temperature, ethanol was added, and the prepared nanocrystals were separated by centrifugation and dispersed in toluene to obtain a ZnTeSe / ZnSeS core / shell quantum dot dispersion.

[0149] Synthesis of First Metal Oxide Nanoparticles

[0150] Synthesis Example 2

[0151] 8.07 mmol zinc acetate dihydrate, 0.93 mmol magnesium acetate tetrahydrate, and 90 mL dimethyl sulfoxide were added to the reactor and heated at 60 °C in air. Subsequently, 15 mmol tetramethylammonium hydroxide pentahydrate was dissolved in 30 mL ethanol to prepare a tetramethylammonium hydroxide pentahydrate solution, which was then slowly added dropwise to the reactor at a rate of 3 mL / min. After stirring the reaction mixture at 60 °C for 1 hour, the prepared Zn... 0.85 Mg 0.15 O nanoparticles were separated using a centrifuge and dispersed in ethanol to obtain Zn. 0.85 Mg 0.15 O nanoparticle dispersion.

[0152] Zn measured using a UT F30 Tecnai electron microscope 0.85 Mg 0.15 The average particle diameter of the O nanoparticles is approximately 3.0 nanometers (nm).

[0153] Synthesis of Second Metal Oxide Nanoparticles

[0154] Synthesis Example 3

[0155] A cerium oxide nanoparticle dispersion was prepared, wherein cerium oxide (CeO2) nanoparticles (796077, Sigma-Aldrich Co., Ltd.) were dispersed in water two or more times at a concentration of 20 wt%, and after each dispersion, the nanoparticles were repeatedly separated by centrifugation to remove excess organic material. The final water-washed cerium oxide nanoparticles were dispersed in ethanol to obtain a cerium oxide nanoparticle dispersion (primary) with a concentration of 2 wt%. When measured by TEM, the cerium oxide nanoparticles were shown to have a particle diameter range of 2.3 ± 0.3 nm, and the amount of organic material in the cerium oxide nanoparticle dispersion was approximately 16 wt%.

[0156] Additional ethanol was added to the cerium oxide nanoparticle dispersion (primary) to finally obtain a cerium oxide nanoparticle dispersion with a concentration of 0.5% by weight.

[0157] Synthesis Example 4

[0158] Cesium carbonate (Cs₂CO₃) was added as an ethanol dispersion having a concentration of 2 wt% to a primary cerium oxide nanoparticle dispersion having a concentration of 2 wt% prepared according to Synthesis Example 3. The two dispersions were mixed at a volume ratio of CeO₂:(Cs₂CO₃) of 91:9 to obtain a cesium-doped cerium oxide (Cs-doped CeO₂) nanoparticle dispersion (primary). Additional ethanol was added to the mixed dispersion to approximately three times the volume of the mixture to obtain a cesium-doped cerium oxide nanoparticle dispersion.

[0159] Synthesis Example 5

[0160] Cesium carbonate (Cs₂CO₃) was added as an ethanol dispersion having a concentration of 2 wt% to a primary cerium oxide nanoparticle dispersion having a concentration of 2 wt% prepared according to Synthesis Example 3. The two dispersions were mixed at a volume ratio of CeO₂:(Cs₂CO₃) of 83:17 to obtain a cesium-doped cerium oxide (Cs-doped CeO₂) nanoparticle dispersion (primary). Additional ethanol was added to the mixed dispersion to approximately three times the volume of the mixture to obtain a cesium-doped cerium oxide nanoparticle dispersion.

[0161] Synthesis Example 6

[0162] Cesium carbonate (Cs₂CO₃) was added as an ethanol dispersion having a concentration of 2 wt% to a primary cerium oxide nanoparticle dispersion having a concentration of 2 wt% prepared according to Synthesis Example 3. The two dispersions were mixed at a volume ratio of CeO₂:(Cs₂CO₃) of 76:24 to obtain a cesium-doped cerium oxide (Cs-doped CeO₂) nanoparticle dispersion (primary). Additional ethanol was added to the mixed dispersion to approximately three times the volume of the mixture to obtain a cesium-doped cerium oxide nanoparticle dispersion.

[0163] Synthesis Example 7

[0164] Cesium carbonate (Cs₂CO₃) was added as an ethanol dispersion having a concentration of 2 wt% to a primary cerium oxide nanoparticle dispersion having a concentration of 2 wt% prepared according to Synthesis Example 3. The two dispersions were mixed at a volume ratio of CeO₂:(Cs₂CO₃) of 68:32 to obtain a cesium-doped cerium oxide (Cs-doped CeO₂) nanoparticle dispersion (primary). Additional ethanol was added to the mixed dispersion to approximately three times the volume of the mixture to obtain a cesium-doped cerium oxide nanoparticle dispersion.

[0165] Fabrication of quantum dot light-emitting devices

[0166] Example 1

[0167] A glass substrate with deposited ITO (WF: 4.8eV) was surface treated with UV-ozone for 15 minutes, and a PEDOT:PSS solution (HCStarks) was spin-coated onto the treated substrate and heat-treated at 150°C for 10 minutes in an air atmosphere, followed by heating at 150°C for 30 minutes in a N2 atmosphere to form a 25nm thick second (or lower) hole transport layer (HOMO: 5.3eV, LUMO: 2.7eV). On the lower hole transport layer, a solution of poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine] (TFB) (Sumitomo) was spin-coated and heat-treated at 150°C for 30 minutes to form a 25 nm thick upper hole transport layer (HOMO: 5.6 eV, LUMO: 2.69 eV). Subsequently, on the upper hole transport layer, a ZnTeSe / ZnSeS core / shell quantum dot dispersion according to Synthesis Example 1 (peak emission wavelength) was spin-coated. The cerium oxide nanoparticle dispersion (0.5 wt%) according to Synthesis Example 3 was spin-coated onto the quantum dot layer and heat-treated at 80°C for 30 minutes to form a 25 nm thick quantum dot layer (HOMO: 5.7 eV, LUMO: 2.97 eV). On the quantum dot layer, a cerium oxide nanoparticle dispersion (0.5 wt%) according to Synthesis Example 3 was spin-coated onto the quantum dot layer and heat-treated at 80°C for 30 minutes to form a 5 nm thick second (or lower) electron transport layer (HOMO: 7.80 eV, LUMO: 4.08 eV). On the second electron transport layer, Zn according to Synthesis Example 2 was spin-coated onto the quantum dot layer. 0.85 Mg 0.15 The nanoparticle dispersion was heat-treated at 80°C for 30 minutes to form a 15 nm thick first (or upper) electron transport layer (HOMO: 8.25 eV, LUMO: 4.55 eV). On the first electron transport layer, aluminum (Al) was vacuum-deposited to form a 90 nm thick second electrode (WF: 4.2 eV), thereby fabricating a quantum dot light-emitting device.

[0168] Example 2

[0169] The quantum dot light-emitting device was fabricated according to the same method as in Example 1, except that the cesium-doped cerium oxide nanoparticle dispersion of Example 4 was used instead of the cerium oxide nanoparticle dispersion of Example 3 to form a 5 nm thick second electron transport layer (HOMO: 7.78 eV, LUMO: 4.06 eV).

[0170] Example 3

[0171] The quantum dot light-emitting device was fabricated according to the same method as in Example 1, except that the cesium-doped cerium oxide nanoparticle dispersion of Synthetic Example 5 was used instead of the cerium oxide nanoparticle dispersion of Synthetic Example 3 to form a 5 nm thick second electron transport layer (HOMO: 7.76 eV, LUMO: 4.03 eV).

[0172] Example 4

[0173] The quantum dot light-emitting device was fabricated according to the same method as in Example 1, except that the cesium-doped cerium oxide nanoparticle dispersion of Example 6 was used instead of the cerium oxide nanoparticle dispersion of Example 3 to form a 5 nm thick second electron transport layer (HOMO: 7.73 eV, LUMO: 4.01 eV).

[0174] Example 5

[0175] The quantum dot light-emitting device was fabricated according to the same method as in Example 1, except that the cesium-doped cerium oxide nanoparticle dispersion of Example 7 was used instead of the cerium oxide nanoparticle dispersion of Example 3 to form a 5 nm thick second electron transport layer (HOMO: 7.72 eV, LUMO: 3.99 eV).

[0176] Comparative Example 1

[0177] The quantum dot light-emitting device is manufactured according to the same method as in Example 1, except that a second electron transport layer is not formed.

[0178] Comparative Example 2

[0179] The quantum dot light-emitting device is manufactured according to the same method as in Example 1, except that a first (or upper) electron transport layer is not formed.

[0180] Comparative Example 3

[0181] The quantum dot light-emitting device was fabricated using the same method as in Example 1, except that the Zn synthesized in Example 2 was used... 0.85 Mg 0.15 O nanoparticle dispersions were spin-coated onto a quantum dot layer and heat-treated at 80°C for 30 minutes to form a 15 nm thick second electron transport layer (HOMO: 8.25 eV, LUMO: 4.55 eV). Cerium oxide nanoparticle dispersions from Synthesis Example 3 were spin-coated onto the second electron transport layer and heat-treated at 80°C for 30 minutes to form a 5 nm thick first electron transport layer (HOMO: 7.80 eV, LUMO: 4.08 eV).

[0182] Evaluation I

[0183] The cesium concentration in the lower electron transport layer of the quantum dot light-emitting device according to the embodiment was analyzed by using X-ray photoelectron spectroscopy (XPS, Quantum 2000, Physical Electronics, Inc.) and ultraviolet (UV) photoelectron spectroscopy (UPS, Versaprobe, Physical Electronics, Inc.).

[0184] Cesium concentration is expressed as a percentage of the number of cesium atoms based on the total number of cerium and cesium atoms in the second electron transport layer.

[0185] The results are shown in Table 1.

[0186] Table 1

[0187] Cs concentration (atomic %) Example 1 0 Example 2 4.75 Example 3 8.98 Example 4 12.67 Example 5 19.02

[0188] Evaluation II

[0189] The current-voltage-luminescence characteristics of the quantum dot light-emitting devices according to the embodiments and comparative examples were evaluated.

[0190] The current-voltage-luminescence characteristics were evaluated using a Keithley 2200 current source and a Minolta CS2000 spectroradiometer.

[0191] The results are shown in Tables 2 and 3.

[0192] Table 2

[0193]

[0194] *Lum max Maximum brightness

[0195] *Cd / A max Maximum current efficiency

[0196] *Cd / m 2 @5mA: Brightness at 5mA

[0197] *λ max Peak emission wavelength

[0198] Table 3

[0199]

[0200] *EQE: External quantum efficiency at 20,000 nits

[0201] *V@5mA: The voltage (turn-on voltage) used for driving at a current of 5mA.

[0202] *V@1000 nits: Voltage used for 1000 nits of light emission.

[0203] Referring to Tables 2 and 3, compared with the quantum dot light-emitting devices according to the comparative examples, the quantum dot light-emitting devices according to the device embodiments exhibit relatively low driving voltages and improved current and luminescence characteristics. In particular, device embodiment 3 (prepared in synthesis example 5), in which the second electron transport layer (ETL) has a cesium content of approximately 9 atomic percent, exhibits a significant improvement in external quantum efficiency compared to devices comparative examples 1 to 3. The 100% improvement compared to device comparative example 1 is quite surprising, as the device structure of comparative example 1 is nearly identical to that of device embodiment 3, except for the presence of a second ETL in device embodiment 3. Furthermore, those skilled in the art will greatly appreciate the lower driving voltages observed in devices embodiments 2 to 5 compared to the comparative example devices and the lower driving voltage of device embodiment 1, which does not contain cesium in the second ETL.

[0204] Evaluation III

[0205] The lifetime characteristics of the quantum dot light-emitting devices according to the embodiments and comparative examples were evaluated. The lifetime characteristics of the quantum dot light-emitting devices were evaluated by measuring the time taken for the brightness to decrease to a selected brightness value relative to the initial brightness value at time t0 when a current with a brightness of 650 nits is injected into the quantum dot light-emitting device. For example, T95 is the time taken for the device to reach 95% of the initial brightness value, and T50 is the time taken for the device to reach 50% of the initial brightness value. Therefore, the larger the values ​​of T95 and / or T50, the longer it takes for the brightness to reach these values, and therefore, the better the lifetime characteristics of the device, measured in hours (hr).

[0206] The results are shown in Table 4.

[0207] Table 4

[0208]

[0209]

[0210] *T95(hr): The time taken for the brightness to decrease to 95% of its initial brightness.

[0211] *T50(hr): The time taken for the brightness to decrease to 50% of its initial brightness.

[0212] *Initial voltage (V0, V): Voltage when the initial brightness is 650 nits.

[0213] *V 1，T50 Voltage at which brightness decreases by 50% relative to the initial brightness

[0214] *ΔV(V): V 1，T50-V0

[0215] Referring to Table 4, the quantum dot light-emitting devices according to the device comparison examples exhibit improved lifetime characteristics. Furthermore, the lifetime data in Table 4 demonstrates the technical importance of adding cesium to the second ETL. Specifically, device examples 2, 3, and 4, with cesium contents of approximately 5.0 atomic%, 9.0 atomic%, and 12.7 atomic%, respectively, show improved lifetime compared to device example 1, while T... 50 The change in the driving voltage difference ΔV is small or non-existent. Furthermore, the technical advantages of adding cesium to the second ETL appear to have upper limits, as indicated by the lifetime data of device embodiment 5 (cesium, 19 atomic percent).

[0216] Although this disclosure has been described with respect to exemplary embodiments which are now considered to be practical, it will be understood that the invention is not limited to the disclosed embodiments, but rather is intended to cover a variety of variations and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. Quantum dot light-emitting devices, including First electrode and second electrode A quantum dot layer between the first electrode and the second electrode A first electron transport layer and a second electron transport layer are disposed between the quantum dot layer and the second electrode, wherein the second electron transport layer is disposed between the quantum dot layer and the first electron transport layer, and each of the first electron transport layer and the second electron transport layer comprises an inorganic material. The lowest unoccupied molecular orbital energy level of the second electron transport layer is shallower than that of the first electron transport layer, and the lowest unoccupied molecular orbital energy level of the quantum dot layer is shallower than that of the second electron transport layer. The first electron transport layer comprises first metal oxide nanoparticles, and The second electron transport layer includes second metal oxide nanoparticles, which are different from the first metal oxide nanoparticles. The condition is that when the first metal oxide nanoparticles include zinc, the second metal oxide nanoparticles include cerium oxide nanoparticles, strontium titanium oxide nanoparticles, niobium oxide nanoparticles, barium tin oxide nanoparticles, or combinations thereof.

2. The quantum dot light-emitting device as described in claim 1, wherein... The energy difference between the lowest unoccupied molecular orbital level of the first electron transport layer and the lowest unoccupied molecular orbital level of the second electron transport layer is 0.01 eV to 1.20 eV, and The energy difference between the lowest unoccupied molecular orbital level of the second electron transport layer and the lowest unoccupied molecular orbital level of the quantum dot layer is 0.01 eV to 1.20 eV.

3. The quantum dot light-emitting device as described in claim 2, wherein... The energy difference between the lowest unoccupied molecular orbital level of the first electron transport layer and the lowest unoccupied molecular orbital level of the second electron transport layer is 0.01 eV to 0.80 eV, and The energy difference between the lowest unoccupied molecular orbital level of the second electron transport layer and the lowest unoccupied molecular orbital level of the quantum dot layer is 0.90 eV to 1.20 eV.

4. The quantum dot light-emitting device as described in claim 1, wherein... The lowest unoccupied molecular orbital energy level of the first electron transport layer is 3.2 eV to 4.8 eV. The lowest unoccupied molecular orbital energy level of the second electron transport layer is 2.8 eV to 4.2 eV, and The lowest unoccupied molecular orbital energy level of the quantum dot layer is 2.5 eV to 3.6 eV.

5. The quantum dot light-emitting device of claim 1, wherein the first metal oxide nanoparticle and the second metal oxide nanoparticle each have an average particle diameter of less than or equal to 10 nanometers.

6. The quantum dot light-emitting device of claim 1, wherein the second electron transport layer comprises an n-type dopant.

7. The quantum dot light-emitting device of claim 6, wherein the n-type dopant comprises a metal element, a metal compound, or a metal salt, including alkali metals, Sn, Ni, Co, Mo, V, Ga, Mn, Fe, Nb, Sr, Ba, In, Ca, Zr, W, Ti, Y, Al, or combinations thereof.

8. The quantum dot light-emitting device of claim 6, wherein the second electron transport layer comprises cerium oxide and cesium, and the cesium is present in an amount of 2 atomic percent to 16 atomic percent based on the total number of cerium and cesium atoms in the second electron transport layer.

9. The quantum dot light-emitting device of claim 7, wherein the n-type dopant comprises Cs, Rb, Li, Na, K, or metal salts derived from cesium carbonate, cesium phosphate, cesium vanadate, cesium azide, lithium nitride, rubidium carbonate, or combinations thereof.

10. The quantum dot light-emitting device of claim 7, wherein the second electron transport layer comprises cerium oxide and cesium salt, and cesium is included in an amount from 0.01 atomic percentage to 40 atomic percentage based on the total number of cerium and cesium atoms in the second electron transport layer.

11. The quantum dot light-emitting device of claim 6, wherein the n-type dopant is included in an amount of 5 to 40 volume percentages based on the second electron transport layer.

12. The quantum dot light-emitting device of claim 1, wherein the first electron transport layer comprises metal oxide nanoparticles, and the metal oxide nanoparticles comprise at least one of the following metals: Zn, Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, or Ba.

13. The quantum dot light-emitting device of claim 12, wherein the first electron transport layer comprises Zn 1-x Q x O represents zinc oxide nanoparticles, where Q is Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Ba, or a combination thereof, and 0 ≤ x < 0.

5.

14. The quantum dot light-emitting device as claimed in claim 1, wherein... The first electron transport layer comprises Zn 1-x Q x O represents zinc oxide nanoparticles, where Q is Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Si, Ba, or combinations thereof, and 0 ≤ x < 0.

5. The second electron transport layer comprises cerium oxide nanoparticles, and The zinc oxide nanoparticles and the cerium oxide nanoparticles each have an average particle diameter of less than or equal to 10 nm.

15. The quantum dot light-emitting device of claim 14, wherein the second electron transport layer further comprises cesium, cesium salt, cesium carbonate, or a combination thereof.

16. The quantum dot light-emitting device of claim 1, wherein the second electron transport layer has a thickness smaller than that of the first electron transport layer.

17. The quantum dot light-emitting device of claim 1, wherein the quantum dot layer comprises cadmium-free quantum dots, and the quantum dot layer emits light having a peak emission wavelength region of 430 nm to 480 nm.

18. An electronic device comprising a quantum dot light-emitting device as claimed in any one of claims 1-17.

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