Quantum dot devices and electronic apparatuses

Abstract

Disclosed are quantum dot devices and electronic devices. The quantum dot device includes a first electrode and a second electrode, a light-emitting layer disposed between the first electrode and the second electrode and including quantum dots, a first charge-assist layer disposed between the second electrode and the light-emitting layer and enhancing transport of first charge carriers from the second electrode to the light-emitting layer, and a buffer layer disposed between the light-emitting layer and the first charge-assist layer and enhancing extraction of second charge carriers from the light-emitting layer.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefits, and all benefits arising therefrom, to Korean Patent Application No. 10-2021-0041122 filed on March 30, 2021 and Korean Patent Application No. 10-2022-0037747 filed on March 28, 2022, the entire contents of which are incorporated herein by reference. Technical Field

[0003] Quantum dot devices and electronic devices have been disclosed. Background Technology

[0004] Semiconductor nanocrystals, also known as quantum dots, can be configured to emit light of a wavelength corresponding to the size of the quantum dot when supplied with light or electrical energy. Therefore, quantum dots can be used as light emitters that emit light of a specific wavelength.

[0005] Research on quantum dot devices that use quantum dots as light emitters has recently attracted attention, and new methods to improve the performance of quantum dot devices are therefore of great significance. Summary of the Invention

[0006] One implementation provides a quantum dot device capable of, for example, exhibiting improved performance.

[0007] One embodiment provides an electronic device including the quantum dot device.

[0008] According to one embodiment, a quantum dot device includes: a first electrode and a second electrode; a light-emitting layer between the first electrode and the second electrode, the light-emitting layer comprising quantum dots; a first charge-assisted layer between the second electrode and the light-emitting layer, the first charge-assisted layer being configured to enhance the transport of first charge carriers from the second electrode to the light-emitting layer; and a buffer layer between the light-emitting layer and the first charge-assisted layer, the buffer layer being configured to enhance the extraction of second charge carriers from the light-emitting layer.

[0009] One of the first charge carrier and the second charge carrier may be an electron, and the other of the first charge carrier and the second charge carrier may be a hole. The first charge carrier may be the primary charge carrier between the second electrode and the light-emitting layer, and the second charge carrier may be the secondary charge carrier between the second electrode and the light-emitting layer.

[0010] The buffer layer can contact the light-emitting layer.

[0011] The first charge-assisted layer and the buffer layer can be in contact with each other.

[0012] The buffer layer may include a first charge-assist material configured to enhance the transport of the first charge carriers and a second charge-assist material configured to enhance the extraction of the second charge carriers, wherein the highest occupied molecular orbital (HOMO) energy level of the second charge-assist material may be lower, for example, shallower, than the HOMO energy level of the first charge-assist material.

[0013] The HOMO level of the second charge-assisted material may be lower than that of the first charge-assisted material by, for example, by about 0.1 eV to about 3.0 eV.

[0014] The first charge-assisted material may be a first electron transport material, and the second charge-assisted material may be a hole extraction material.

[0015] The first charge-assisted material may include n-type inorganic nanoparticles, and the second charge-assisted material may include p-type non-polymer materials (e.g., p-type non-polymer organic materials), p-type polymers, p-type inorganic materials, p-type organic-inorganic materials, or combinations thereof.

[0016] The conductivity of the second charge carriers in the second charge-assisted material can be greater than that in the first charge-assisted material.

[0017] The second charge-assisting material may be present in a smaller amount than the first charge-assisting material in the buffer layer.

[0018] In the buffer layer, based on the total amount of the first charge-assisted material and the second charge-assisted material, the second charge-assisted material may be present in an amount of about 0.1 wt% to about 15 wt%.

[0019] The first charge-assisted layer may include a second electron transport material, which may be the same as or different from the first electron transport material.

[0020] The thickness of the buffer layer may be the same as or thinner than the thickness of the first charge-assisted layer.

[0021] The conductivity of the second charge carriers in the buffer layer can be greater than that of the second charge carriers in the first charge-assisted layer, and the conductivity of the second charge carriers in the buffer layer can be greater than that of the second charge carriers in the light-emitting layer.

[0022] The quantum dot device may further include a second charge-assisted layer between the first electrode and the light-emitting layer, the second charge-assisted layer being configured to enhance the transport of the second charge carrier from the first electrode to the light-emitting layer, wherein the second charge carrier may be the dominant charge carrier between the first electrode and the light-emitting layer.

[0023] According to one embodiment, a quantum dot device includes: a first electrode and a second electrode; a light-emitting layer between the first electrode and the second electrode, the light-emitting layer comprising quantum dots; a buffer layer between the second electrode and the light-emitting layer, the buffer layer comprising a first electron transport material and a hole extraction material; and a first charge-assisted layer between the second electrode and the light-emitting layer, the first charge-assisted layer comprising a second electron transport material that is the same as or different from the first electron transport material, wherein the buffer layer is closer to the light-emitting layer than the first charge-assisted layer.

[0024] The hole-extraction material in the buffer layer may be present in a smaller amount than the first electron transport material.

[0025] The first electron transport material, the hole extraction material, the second electron transport material, or a combination thereof may include inorganic nanoparticles.

[0026] The hole conductivity of the buffer layer can be greater than that of the first charge-assisted layer, and the hole conductivity of the buffer layer can be greater than that of the light-emitting layer.

[0027] The quantum dot device may further include a second charge-assisted layer between the first electrode and the light-emitting layer, the second charge-assisted layer comprising a hole transport material.

[0028] According to one embodiment, a quantum dot device includes: a first electrode and a second electrode; a light-emitting layer between the first electrode and the second electrode, the light-emitting layer comprising quantum dots; a first charge-assisted layer between the second electrode and the light-emitting layer, the first charge-assisted layer being an electron-assisted layer; and a buffer layer between the light-emitting layer and the first charge-assisted layer, wherein the hole conductivity of the buffer layer is greater than the hole conductivity of the first charge-assisted layer, and wherein the hole conductivity of the buffer layer is greater than the conductivity of the light-emitting layer.

[0029] The first electrode may be an anode, the second electrode may be a cathode, and the buffer layer may include a hole extraction material.

[0030] The buffer layer may further include n-type inorganic nanoparticles.

[0031] The first charge-assisted layer and the buffer layer may each comprise the same or different n-type inorganic nanoparticles.

[0032] According to one embodiment, an electronic device including the quantum dot device is provided.

[0033] The performance of quantum dot devices can be improved. Attached Figure Description

[0034] The above and other advantages and features of this disclosure will become clearer from a more detailed description of exemplary embodiments thereof with reference to the accompanying drawings, in which: Figure 1 A schematic cross-sectional view illustrating the quantum dot device according to an embodiment. Detailed Implementation

[0035] Hereinafter, embodiments of the present disclosure will be described in detail so that those skilled in the art will understand them. However, the present disclosure may be embodied in many different forms and is not to be construed as limited to the exemplary embodiments set forth herein.

[0036] In the accompanying drawings, the thicknesses of layers, films, panels, regions, etc., are enlarged for clarity. Throughout the specification, the same reference numerals consistently 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. 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 portions, these elements, components, regions, layers, and / or portions should not be limited by these terms. These terms are used only to distinguish one element, component, region, layer, or portion from another element, component, region, layer, or portion. Therefore, without departing from the teachings herein, the first element, component, region, layer, or portion discussed below may be referred to as the second element, component, region, layer, or portion.

[0037] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, “a,” “the,” and “at least one” do not indicate a limitation of quantity and are intended to include both the singular and the plural unless the context clearly indicates otherwise. For example, “element” has the same meaning as “at least one element” unless the context clearly indicates otherwise. “At least one” will not be construed as limited to “a” or “an.” “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 collections thereof.

[0038] Furthermore, relative terms such as “lower” and “upper” 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 orientation shown in the figures, relative terms are also intended to cover 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 will be oriented on the “upper” side of said other element. Thus, depending on the specific orientation of the figure, the exemplary term “lower” can cover both “lower” and “upper” orientations. Similarly, if the device in one of the figures is flipped, the element described as being “below” or “under” other elements will be oriented “above” said other elements. Thus, the exemplary terms “below” or “under” can cover both “above” and “below” orientations.

[0039] As used herein, “about” includes the stated value and means within an acceptable range of deviations from the specific value, as determined by one of ordinary skill 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 a deviation from the stated value of no more than one or more standard deviations, or no more than ±10% or 5%.

[0040] Unless otherwise defined, all terms used herein (including technical and scientific terms) 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 common dictionaries, should be interpreted as having the same meaning as they have in the context of this disclosure and the relevant field, and will not be interpreted in an idealized or overly formal sense unless clearly defined herein.

[0041] Exemplary embodiments are described herein with reference to cross-sectional views that serve as schematic representations of idealized embodiments. Thus, deviations from the shapes depicted in the figures will be anticipated as a result of, for example, manufacturing techniques and / or tolerances. Therefore, the embodiments described herein should not be construed as limited to the specific shapes of the regions illustrated herein, but rather include deviations in shape caused, for example, by manufacturing processes. For example, regions illustrated or described as flat may typically have rough and / or non-linear characteristics. Furthermore, sharp corners in the figures may be rounded. Therefore, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shapes of the regions nor to limit the scope of the claims. Hereinafter, the term "combination" includes mixtures or stacked structures of two or more.

[0042] As used herein, unless otherwise specifically defined, energy levels refer to the highest occupied molecular orbital (HOMO) energy level and the lowest unoccupied molecular orbital (LUMO) energy level.

[0043] In the following text, the work function (WF), HOMO level, or LUMO level are expressed as absolute values ​​of distance from the vacuum level. Furthermore, when the work function, HOMO level, or LUMO level is referred to as deep, high, or large, it may have a large absolute value based on the vacuum level of "0 eV," while when the work function, HOMO level, or LUMO level is referred to as shallow, low, or small, it may have a small absolute value based on the vacuum level of "0 eV."

[0044] The HOMO level and work function can be measured by ultraviolet photoelectron spectroscopy (UPS), and the LUMO level can be calculated from the HOMO level and the band gap energy obtained at the absorption peak.

[0045] As used herein, the phrase "excluding cadmium (or other harmful heavy metals)" means that the concentration of cadmium (or harmful heavy metals) may be less than or equal to about 100 parts per million (ppmw), less than or equal to about 50 ppmw, less than or equal to about 10 ppmw, or almost zero. In embodiments, cadmium (or other heavy metals) may be substantially absent, or if present, the amount of cadmium (or other heavy metals) may be less than or equal to the detection limit of a given analytical tool or as an impurity level.

[0046] As used in this article, the term "group" in terms such as Group II, Group III, etc., refers to a group in the periodic table of elements.

[0047] As used herein, “Group I” can refer to Group IA and Group IB and instances of Group I elements can be Li, Na, K, Rb, or Cs, but are not limited thereto.

[0048] As used in this article, “Group II” may refer to Group IIA and Group IIB, and examples of Group II metals may be Cd, Zn, Hg, and Mg, but are not limited thereto.

[0049] As used herein, “Group III” may refer to Group IIIA and Group IIIB, and examples of Group III metals may be Al, In, Ga, and Tl, but are not limited thereto.

[0050] As used herein, “Group IV” may refer to Group IVA and Group IVB, and examples of Group IV metals may be Si, Ge, and Sn, but are not limited thereto. As used herein, the term “metal” may include half-metals such as Si.

[0051] As used herein, “group V” may refer to group VA, and examples may include, but are not limited to, nitrogen, phosphorus, arsenic, antimony, and bismuth.

[0052] As used herein, “VI group” may refer to VIA group, and examples may include, but are not limited to, sulfur, selenium, and tellurium.

[0053] In the following description, a quantum dot device according to an embodiment is illustrated with reference to the accompanying drawings.

[0054] According to the embodiments, the quantum dot device can be a quantum dot electroluminescent device that emits light from the quantum dot by applying an electric field to the electrodes.

[0055] Figure 1 A schematic cross-sectional view illustrating the quantum dot device according to an embodiment.

[0056] Reference Figure 1 The quantum dot device 10 according to an embodiment includes: a first electrode 11 and a second electrode 12 facing each other; a light-emitting layer 13 between the first electrode 11 and the second electrode 12; a first charge-assisted layer 14 between the second electrode 12 and the light-emitting layer 13; a buffer layer 15 between the second electrode 12 and the light-emitting layer 13; and a second charge-assisted layer 16 between the first electrode 11 and the light-emitting layer 13. Compared with the first charge-assisted layer 14, the buffer layer 15 may be closer to the light-emitting layer 13.

[0057] A substrate (not shown) may be disposed below the first electrode 11 or on 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.

[0058] 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.

[0059] The first electrode 11 may be made of a conductor having a relatively high work function, such as a metal, a conductive metal oxide, or a combination thereof. The first electrode 11 may be made of, for example, 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.

[0060] The second electrode 12 may be made of 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, a conductive polymer, or a combination thereof. The second electrode 12 may include, for example, metals such as aluminum, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, silver, tin, lead, cesium, barium, or alloys thereof; and multilayer structure materials such as LiF / Al, Li2O / Al, lithium 8-hydroxyquinoline (Liq) / Al, LiF / Ca, and BaF2 / Ca, but is not limited thereto.

[0061] The work function of the first electrode 11 may be greater than that of the second electrode 12. For example, the work function of the first electrode 11 may be about 4.5 eV to about 5.0 eV and the work function of the second electrode 12 may be about 4.0 eV to about 4.7 eV. Within the scope of the disclosure, the work function of the first electrode 11 may be about 4.6 eV to about 4.9 eV and the work function of the second electrode 12 may be about 4.0 eV to about 4.5 eV.

[0062] The first electrode 11, the second electrode 12, or a combination thereof may be light-transmitting electrodes, and the light-transmitting electrodes may be made, for example, of conductive oxides such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or fluorine-doped tin oxide, or single or multiple metal thin layers. The first electrode 11 or the second electrode 12 may be opaque electrodes, and the opaque electrodes may be made of, for example, opaque conductors such as aluminum (Al), silver (Ag), or gold (Au).

[0063] The light-emitting layer 13 includes quantum dots (a plurality of quantum dots, hereinafter referred to as "quantum dots") as light emitters configured to emit light through an electric field. Quantum dots, broadly speaking, refer to semiconductor nanocrystals and can exhibit quantum confinement effects. The quantum dots can have any suitable shape and are not particularly limited. In non-limiting examples, the quantum dots can have various shapes, such as spherical semiconductor nanocrystals, quantum rods, quantum sheets, or combinations thereof. A quantum rod can refer to a quantum dot having an aspect ratio (length-to-diameter 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, the aspect ratio of the quantum rod can be 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.

[0064] The quantum dots may have (average) sizes, such as about 1 nanometer (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, for example, particle diameter (for non-spherical shapes, average maximum particle diameter (size)). In examples, the (average) size of the quantum dots may be greater than or equal to about 1 nm, greater than or equal to about 2 nm, greater than or equal to about 3 nm, greater than or equal to about 4 nm, greater than or equal to about 5 nm, greater than or equal to about 6 nm, greater than or equal to about 7 nm, greater than or equal to about 8 nm, greater than or equal to about 9 nm, greater than or equal to about 10 nm, greater than or equal to about 11 nm, or greater than or equal to about 12 nm. In examples, the (average) size of the quantum dots may be less than or equal to about 50 nm, less than or equal to about 40 nm, less than or equal to about 30 nm, less than or equal to about 25 nm, less than or equal to about 20 nm, less than or equal to about 19 nm, less than or equal to about 18 nm, less than or equal to about 17 nm, less than or equal to about 16 nm, or less than or equal to about 15 nm. For example, the average size of the quantum dots (e.g., emitting blue light) may be, for example, less than or equal to about 4.5 nm, for example, 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. In examples, the (average) size of the quantum dots may be 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.

[0065] The bandgap energy of a quantum dot can be tuned by changing the size, composition, or a combination thereof of the quantum dot, and the emission wavelength can be tuned accordingly. For example, as the size of the quantum dot increases, the bandgap energy can decrease, for example, become narrower, and thus, light with a relatively long wavelength spectrum can be emitted. As the size of the quantum dot decreases, the bandgap energy can increase, for example, become wider, and thus, light with a relatively short wavelength spectrum can be emitted.

[0066] For example, the quantum dots can be configured, depending on their size, composition, or combinations thereof, to emit light of a predetermined wavelength spectrum, for example, in the visible light region. For instance, the quantum dots can be configured to emit blue, red, or green light, with blue light having a peak emission wavelength in the region of about 430 nm to about 480 nm, red light having a peak emission wavelength in the region of about 600 nm to about 670 nm, and green light having a peak emission wavelength in the region of about 500 nm to about 560 nm.

[0067] In the quantum dot device 10 of the example, the maximum emission wavelength of the light-emitting layer 13 may be greater than or equal to about 300 nm, greater than or equal to about 400 nm, greater than or equal to about 430 nm, greater than or equal to about 450 nm, for example, greater than or equal to about 500 nm, greater than or equal to about 510 nm, greater than or equal to about 520 nm, greater than or equal to about 530 nm, greater than or equal to about 540 nm, greater than or equal to about 550 nm, greater than or equal to about 560 nm, greater than or equal to about 570 nm, greater than or equal to about 580 nm, greater than or equal to about 590 nm, greater than or equal to about 600 nm, or greater than or equal to about 610 nm. The maximum emission wavelength of the quantum dot can be within the following ranges: less than or equal to about 800 nm, less than or equal to about 780 nm, less than or equal to about 750 nm, for example, less than or equal to about 700 nm, less than or equal to about 670 nm, less than or equal to about 650 nm, less than or equal to about 640 nm, less than or equal to about 630 nm, less than or equal to about 620 nm, less than or equal to about 610 nm, less than or equal to about 600 nm, less than or equal to about 590 nm, less than or equal to about 580 nm, less than or equal to about 570 nm, less than or equal to about 560 nm, less than or equal to about 550 nm, or less than or equal to about 540 nm. The maximum emission wavelength of the quantum dot can be in the range of about 430 nm to about 670 nm.

[0068] In the example quantum dot device 10, the light-emitting layer 13 or the quantum dot can be configured to emit green light, and the maximum emission wavelength can be in the range of greater than or equal to about 500 nm (e.g., greater than or equal to about 510 nm or greater than or equal to about 520 nm) and less than or equal to about 560 nm (e.g., less than or equal to about 550 nm or less than or equal to about 540 nm). In the example quantum dot device 10, the light-emitting layer 13 or the quantum dot can be configured to emit red light, and the maximum emission wavelength can be in the range of greater than or equal to about 600 nm (e.g., greater than or equal to about 610 nm) and less than or equal to about 670 nm (e.g., less than or equal to about 650 nm or less than or equal to about 640 nm). In the example quantum dot device 10, the light-emitting layer 13 or the quantum dot can be configured to emit blue light and the maximum emission wavelength can be in the range of greater than or equal to about 430 nm (e.g., greater than or equal to about 440 nm or greater than or equal to about 450 nm) and less than or equal to about 480 nm (e.g., less than or equal to about 470 nm or less than or equal to about 465 nm).

[0069] The quantum dot may have a quantum yield of about 10%, for example, about 20%, about 30%, about 50%, about 60%, about 70%, or about 90%.

[0070] The emission spectrum of the quantum dot may have a relatively narrow half-width (FWHM). Here, FWHM is the wavelength width corresponding to half of the maximum emission point in the emission spectrum. By applying a quantum dot with an emission spectrum having a relatively narrow FWHM and an emitting layer 13 including therein to a quantum dot device 10, for example, including the quantum dot and an emitting layer including therein in the quantum dot device, it is possible to provide, for example, high color purity (or color reproducibility).

[0071] The FWHM of the quantum dot (or emitting layer 13) may be, for example, less than or equal to about 60 nm, less than or equal to about 55 nm, less than or equal to about 52 nm, 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. m, or less than or equal to about 28nm, for example, about 2nm-about 60nm, about 2nm-about 55nm, about 2nm-about 50nm, about 2nm-about 49nm, about 2nm-about 48nm, about 2nm-about 47nm, about 2nm-about 46nm, about 2nm-about 45nm, about 2nm-about 44nm, about 2nm-about 43nm, about 2nm-about 42nm, about 2nm-about 41nm, about 2nm-about 40nm, about 2nm-about 39nm, about 2nm-about 38nm, about 2nm-about 37nm, about 2nm-about 36nm, about 2nm-about 35nm, about 2nm-about 34nm, about 2nm-about 33nm, about 2nm-about 32nm, about 2nm-about 31nm, about 2nm-about 30nm, about 2nm-about 29nm, or about 2nm-about 28nm.

[0072] For example, the quantum dots may include 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.

[0073] The group II-VI semiconductor compounds may be, for example: binary compounds such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or combinations thereof; ternary compounds such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZn Te, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, or combinations thereof; or quaternary compounds such as 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; or 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 group 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; or 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; or 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.

[0074] The single-element semiconductor, binary semiconductor compound, ternary semiconductor compound, or quaternary semiconductor compound may be included in the quantum dot at a substantially uniform concentration or in a state with locally different concentration distributions.

[0075] For example, the quantum dots may include cadmium-free (Cd) quantum dots. Cadmium (Cd) can cause 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. In an example, the luminescent layer 13 may not include cadmium. Examples of luminescent layer 13 may not include cadmium, lead, mercury, or combinations thereof.

[0076] As an example, the quantum dot may be a semiconductor compound comprising at least one of tellurium (Te) and selenium (Se) and zinc (Zn). For example, the quantum dot may be a Zn-Te semiconductor compound, a Zn-Se semiconductor compound, a Zn-Te-Se semiconductor compound, or a combination thereof. For example, the molar fraction of tellurium (Te) in the Zn-Te-Se semiconductor compound may be less than the molar fraction of selenium (Se). The semiconductor compound may have a maximum emission wavelength in a wavelength spectrum less than or equal to about 480 nm, for example, about 430 nm to about 480 nm, and may be configured to emit blue light.

[0077] For example, the quantum dot may be a semiconductor compound comprising zinc (Zn), phosphorus (P), or a combination thereof, and indium (In). For example, the quantum dot may be an In-P semiconductor compound, an In-Zn-P semiconductor compound, or a combination thereof. 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, for example, about 25:1 to about 100:1 or about 250:1.

[0078] The quantum dots may have a core-shell structure in which one quantum dot surrounds another quantum dot. For example, the core and shell of the quantum dot may have an interface, and the elements of the core, the shell, or a combination thereof at the interface may have a concentration gradient in which the concentration of one or more elements of the shell decreases toward the core. For example, the material composition of the shell of the quantum dot may have a larger, for example, higher bandgap energy compared to the material composition of the core of the quantum dot, and the quantum dot may exhibit a quantum confinement effect.

[0079] 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, have a concentration gradient, or a combination thereof.

[0080] For example, the multilayer shell, the shell furthest from the core, may have a larger, for example, higher bandgap energy compared to the shell closest to the core, and the quantum dot may exhibit a quantum confinement effect.

[0081] For example, the quantum dot having a core-shell structure may include, for example, a core comprising a first semiconductor compound including tellurium (Te), selenium (Se), or a combination thereof, and zinc (Zn); and a shell disposed on at least a portion of the core and comprising a second semiconductor compound having a composition different from that of the core.

[0082] 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 small amount of tellurium (Te), for example, a ZnTe x Se 1-x The semiconductor compound is represented by x, where x is greater than about 0 and less than or equal to 0.05.

[0083] For example, in the first semiconductor compound based on Zn-Te-Se, the molar fraction of zinc (Zn) may be greater than the molar fraction of selenium (Se), and the molar fraction of selenium (Se) may be greater than the molar fraction 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 approximately 0.025:1, less than or equal to approximately 0.024:1, less than or equal to approximately 0.023:1, less than or equal to approximately 0.022:1, less than or equal to approximately 0.021:1, less than or equal to approximately 0.02:1, less than or equal to approximately 0.019:1, less than or equal to approximately 0.018:1, less than or equal to approximately 0.017:1, less than or equal to approximately 0.016:1, less than or equal to approximately 0.015:1, less than or equal to approximately 0.014:1, less than or equal to approximately 0.013:1, less than or equal to approximately 0.012:1, less than or equal to approximately 0.011:1, or less than or equal to approximately 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.

[0084] 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 herein.

[0085] For example, the second semiconductor compound may include zinc (Zn) and selenium (Se), sulfur (S), or combinations thereof. For example, the shell may include ZnSeS, ZnS, or combinations thereof. For example, the shell may include an inner shell disposed near the core, for example, at least one inner shell disposed near the core, and an outermost shell disposed at the outermost edge of the quantum dot. 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 the content of, for example, sulfur (S) may increase as it leaves the core.

[0086] For example, a quantum dot having a core-shell structure may include: a core comprising a third semiconductor compound including zinc (Zn), phosphorus (P), or a combination thereof, and indium (In); and a 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.

[0087] 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.

[0088] 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 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 herein.

[0089] 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 combinations thereof. For example, the shell may include an inner shell disposed near the core, for example, at least one inner shell disposed near the core, and an outermost shell disposed at the outermost edge of the quantum dot. The inner shell, the outermost shell, or combinations thereof may include a fourth semiconductor compound of ZnS or ZnSeS.

[0090] The aforementioned quantum dots are commercially available or can be appropriately synthesized.

[0091] In the quantum dot device 10 of the example, the quantum dot may include a first organic ligand on its surface. The first organic ligand may have a hydrophobic portion. The first organic ligand may be bound to the surface of the quantum dot. The first organic ligand may include RCOOH, RNH2, R2NH, R3N, RSH, R3PO, R3P, ROH, RCOOR, RPO(OH)2, RHPOOH, R2POOH, or combinations thereof, wherein each R is independently a substituted or unsubstituted C3(C5)-C40 aliphatic hydrocarbon group, such as a substituted or unsubstituted C3-C40 alkyl, alkenyl, etc., a substituted or unsubstituted C6-C40 aromatic hydrocarbon group, such as a substituted or unsubstituted C6-C40 aryl, etc., or combinations thereof.

[0092] Examples of the organic ligands may be thiols such as methanethiol, ethanethiol, propanethiol, butanethiol, pentylenetetrazol, hexanethiol, octylthiol, dodecylthiol, hexadecylthiol, octadecylthiol, benzylthiol, etc.; amines such as methylamine, ethylamine, propylamine, butylamine, pentylemine, hexylamine, octylamine, nonylamine, decylamine, dodecylamine, hexadecylamine, octadecylamine, dimethylamine, diethylamine, dipropylamine, tributylamine, trioctylamine, etc.; carboxylic acids such as formic acid, acetic acid, propionic acid, butyric acid, valeric acid, hexanoic acid, heptanoic acid, octanoic acid, dodecanoic acid, hexadecanoic acid, octadecanoic acid, oleic acid, benzoic acid, etc.; and phosphine compounds such as methylphosphine, ethylphosphine, propylphosphine, butylphosphine, pentylenetetrazine, octylphosphine, etc. The quantum dots may include, but are not limited to, dioctylphosphine, tributylphosphine, trioctylphosphine, etc.; phosphine oxide compounds such as methylphosphine oxide, ethylphosphine oxide, propylphosphine oxide, butylphosphine oxide, pentylphosphine oxide, tributylphosphine oxide, octylphosphine oxide, dioctylphosphine oxide, trioctylphosphine oxide, etc.; diphenylphosphine compounds, triphenylphosphine compounds, or their oxides; C5-C20 alkylphosphino acids such as hexylphosphino acid, octylphosphino acid, dodecylphosphino acid, tetradecylphosphino acid, hexadecylphosphino acid, octadecylphosphino acid, etc.; C5-C20 alkylphosphino acids such as hexylphosphino acid, octylphosphino acid, dodecylphosphino acid, tetradecylphosphino acid, hexadecylphosphino acid, octadecylphosphino acid, etc.; and so on. The quantum dots may include a single type of hydrophobic organic ligand or may use two or more types of hydrophobic organic ligands.

[0093] In addition to organic ligands (e.g., fatty acid compounds with C5 or larger or C10 or larger, such as oleic acid), the quantum dots may further include halogens on their surface (hereinafter referred to as "halogenated quantum dots" or "halogenated quantum dots"). The halogen content in the halogenated quantum dots may be, for example, greater than or equal to about 1 microgram (μg), greater than or equal to about 1.5 μg, greater than or equal to about 3 μg, greater than or equal to about 4 μg, greater than or equal to about 5 μg, greater than or equal to about 6 μg, greater than or equal to about 7 μg, greater than or equal to about 8 μg, greater than or equal to about 9 μg, greater than or equal to about 10 μg, greater than or equal to about 11 μg, greater than or equal to about 12 μg, greater than or equal to about 12.5 μg, greater than or equal to about 13 μg, or greater than or equal to... The halogen may be chlorine, and may be found in amounts of about 14 μg, greater than or equal to about 15 μg, greater than or equal to about 16 μg, greater than or equal to about 17 μg, greater than or equal to about 18 μg, or greater than or equal to about 19 μg and less than about 30 μg, less than or equal to about 25 μg, less than or equal to about 20 μg, less than or equal to about 19.5 μg, less than or equal to about 19 μg, less than or equal to about 18 μg, less than or equal to about 17 μg, less than or equal to about 15 μg, less than or equal to about 12.5 μg, or less than or equal to about 12 μg, as determined by ion chromatography.

[0094] An example of a method for preparing the halogen-treated quantum dots may include: obtaining an organic dispersion comprising a first organic solvent and a plurality of quantum dots comprising a first organic ligand on a surface; obtaining a chloride solution comprising a metal halide and a polar organic solvent miscible with the first organic solvent; and adding the chloride solution to the organic dispersion such that, based on the total weight of the quantum dots, the content of the metal halide is greater than or equal to about 0.1% by weight and less than or equal to about 10% by weight; and then stirring the result at a temperature greater than or equal to about 45°C, for example, greater than or equal to about 50°C, greater than or equal to about 55°C, or greater than or equal to about 60°C and less than or equal to about 150°C, less than or equal to about 140°C, less than or equal to about 100°C, less than or equal to about 90°C, less than or equal to about 80°C, or less than or equal to about 70°C. The volume ratio of the polar organic solvent to the first organic solvent may be less than or equal to about 0.1:1.

[0095] The metal halide (e.g., metal chloride) may include zinc halide, indium halide, gallium halide, magnesium halide, lithium halide, or combinations thereof. The first organic solvent may include substituted or unsubstituted C5-C40 aliphatic hydrocarbons, substituted or unsubstituted C6-C40 aromatic hydrocarbons, substituted or unsubstituted C3-C40 alicyclic hydrocarbons, or combinations thereof. The polar organic solvent may include C1-C10 alcohols (e.g., methanol, ethanol, propanol, isopropanol, butanol, pentanol, hexanol, heptanol, etc.) or combinations thereof.

[0096] The thickness of the light-emitting layer 13 can be, for example, about 5 nm to about 200 nm, about 10 nm to about 150 nm, about 20 nm to about 100 nm, or about 20 nm to about 80 nm.

[0097] The light-emitting layer 13 may have a single layer or a multilayer structure of two or more layers stacked together. In the multilayer structure, adjacent layers (e.g., a first light-emitting layer and a second light-emitting layer) may have the same or different physical properties / compositions. At least one of the light-emitting layers 13 may further include a halogen (e.g., chlorine). The light-emitting layer 13 may exhibit a halogen content that varies in the thickness direction.

[0098] The light-emitting layer 13 of the example may exhibit a carbon content that varies along the thickness direction. In one example of the light-emitting layer 13, the carbon content may increase as it approaches the buffer layer 15. In another example of the light-emitting layer 13, the carbon content may decrease as it approaches the buffer layer 15.

[0099] Examples of the light-emitting layer 13 may include a layer comprising quantum dots and having a halogen-treated (e.g., chlorine) surface (hereinafter referred to as a surface-treated first light-emitting layer or first layer). A second layer comprising the halogen-treated quantum dots, a third layer comprising quantum dots having organic ligands, or a combination thereof may be disposed on the first layer. The second layer may be between the first layer and the third layer. The organic material (e.g., carbon) content (e.g., concentration) of the first layer may be lower than that of the second layer. The halogen (e.g., chlorine) content (e.g., concentration) of the first layer may be greater than that of the second layer. The organic material content of the first layer may be greater than that of the second layer. The halogen content of the first layer may be lower than that of the second layer. The organic material content of the light-emitting layer 13 may be controlled by suitable means (for post-processing of the formed layer).

[0100] The emitting layer 13 may have relatively deep HOMO energy levels, for example, HOMO energy levels greater than or equal to about 5.4 eV, such as 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 the luminescent layer 13 can be, for example, approximately 5.4 eV to approximately 7.0 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, approximately 5.6 eV to approximately 6.7 eV, approximately 5.6 eV to approximately 6.5 eV, approximately 5.6 eV to approximately 6.3 eV, approximately 5.6 eV to approximately 6.2 eV, approximately 5.6 eV to approximately 6.1 eV, approximately 5.7 eV to approximately 7.0 eV, approximately 5.7 eV to approximately 6.8 eV, and approximately 5.7 eV. - Approximately 6.7 eV, approximately 5.7 eV - approximately 6.5 eV, approximately 5.7 eV - approximately 6.3 eV, approximately 5.7 eV - approximately 6.2 eV, approximately 5.7 eV - approximately 6.1 eV, approximately 5.8 eV - approximately 7.0 eV, approximately 5.8 eV - approximately 6.8 eV, approximately 5.8 eV - approximately 6.7 eV, approximately 5.8 eV - approximately 6.5 eV, approximately 5.8 eV eV - about 6.3 eV, about 5.8 eV - about 6.2 eV, about 5.8 eV - about 6.1 eV, about 6.0 eV - about 7.0 eV, about 6.0 eV - about 6.8 eV, about 6.0 eV - about 6.7 eV, about 6.0 eV - about 6.5 eV, about 6.0 eV - about 6.3 eV, or about 6.0 eV - about 6.2 eV.

[0101] The luminescent layer 13 may have a relatively shallow LUMO energy level, for example less than or equal to about 3.6 eV, less than or equal to about 3.5 eV, for example less than or equal to about 3.4 eV, for example less than or equal to about 3.3 eV, for example less than or equal to about 3.2 eV, or for example less than or equal to about 3.0 eV. The LUMO energy levels of the luminescent layer 13 can 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.

[0102] The light-emitting layer 13 may have a band gap energy of about 2.4 eV to about 2.9 eV. Within the scope of the disclosure, the light-emitting layer 13 may have a band gap energy of, for example, about 2.4 eV to about 2.8 eV, or about 2.4 eV to about 2.78 eV.

[0103] The first charge-assisted layer 14 and the buffer layer 15 are disposed between the second electrode 12 and the light-emitting layer 13.

[0104] The first charge-assisted layer 14 may be a functional layer configured to improve the electrical performance between the second electrode 12 and the light-emitting layer 13. The first charge-assisted layer 14 may increase the transport of the first charge carriers from the second electrode 12 to the light-emitting layer 13 and may block the reverse injection of the second charge carriers from the light-emitting layer 13 to the second electrode 12. One of the first charge carriers and the second charge carrier may be an electron and the other may be a hole. The first charge carrier may be the dominant charge carrier (also referred to as the majority charge carrier) between the second electrode 12 and the light-emitting layer 13, and the second charge carrier may be the minor charge carrier (also referred to as the minority charge carrier) between the second electrode 12 and the light-emitting layer 13.

[0105] For example, when the second electrode 12 can be a cathode, the first charge carrier can be an electron and the second charge carrier can be a hole, and the first charge auxiliary layer 14 can be an electron auxiliary layer, such as an electron transport layer, an electron injection layer, a hole blocking layer, or a combination thereof.

[0106] For example, when the second electrode 12 is the anode, the first charge carrier can be a hole and the second charge carrier can be an electron, and the first charge auxiliary layer 14 can be a hole auxiliary layer, such as a hole transport layer, a hole injection layer, an electron blocking layer, or a combination thereof.

[0107] The first charge-assisted layer 14 may have one, two or more layers and may, for example, be in contact with the second electrode 12.

[0108] The first charge-assisted layer 14 may include a charge-transport material, such as an electron-transport material. For example, the first charge-assisted layer 14 may include inorganic nanoparticles. The inorganic nanoparticles may be, for example, oxide nanoparticles, such as metal oxide nanoparticles. For example, the inorganic nanoparticles may be metal oxide nanoparticles comprising two or more types of metals. For example, the inorganic nanoparticles may be inorganic semiconductors. For example, the inorganic nanoparticles may be n-type inorganic nanoparticles.

[0109] The inorganic nanoparticles may be two-dimensional or three-dimensional nanoparticles having an average particle diameter of, for example, about 10 nm, about 8 nm, about 7 nm, about 5 nm, about 4 nm, or about 3.5 nm, for example, 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.

[0110] Compared to the LUMO energy level of the luminescent layer 13, the LUMO energy level of the inorganic nanoparticles (or the first charge-assisted layer 14) may be deeper or shallower. For example, the LUMO energy level of the inorganic nanoparticles (or the first charge-assisted layer 14) may be deeper than the LUMO energy level of the luminescent layer 13. The difference between the LUMO energy level of the inorganic nanoparticles (or the first charge-assisted layer 14) and the LUMO energy level of the luminescent layer 13 may be, for example, less than or equal to about 2.5 eV, less than or equal to about 2.3 eV, less than or equal to about 2.0 eV, less than or equal to about 1.8 eV, less than or equal to about 1.0 eV, less than or equal to about 0.5 eV, less than or equal to about 0.3 eV, or less than or equal to about 0.2 eV. The LUMO energy level of the inorganic nanoparticles (or the first charge-assisted layer 14) may be, for example, about 2.5 eV to about 4.8 eV, about 2.6 eV to about 4.6 eV, or about 2.7 eV to about 4.5 eV.

[0111] Compared to, for example, the HOMO level of the light-emitting layer 13, the HOMO level of the inorganic nanoparticles (or the first charge-assisted layer 14) can be deeper. For example, the HOMO level of the inorganic nanoparticles (or the first charge-assisted layer 14) can be greater than or equal to about 0.2 eV, greater than or equal to about 0.5 eV, greater than or equal to about 0.8 eV, greater than or equal to about 1.0 eV, greater than or equal to about 1.2 eV, or greater than or equal to about 1.5 eV, for example, about 0.2 eV to about 3.0 eV, about 0.5 eV to about 3.0 eV, about 0.8 eV to about 3.0 eV, about 1.0 eV to about 3.0 eV, about 1.2 eV to about 3.0 eV, or about 1.5 eV to about 2.0 eV.

[0112] For example, the inorganic nanoparticles (or the first charge-assisted layer 14) may have relatively deep HOMO energy levels, and the HOMO energy levels of the inorganic nanoparticles (or the first charge-assisted layer 14) may be, for example, about 5.6 eV to about 8.5 eV, about 5.8 eV to about 8.2 eV, about 6.0 eV to about 8.0 eV, about 6.2 eV to about 8.0 eV, about 6.5 eV to about 8.0 eV, about 6.8 eV to about 8.0 eV, about 7.0 eV to about 8.0 eV, about 7.2 eV to about 7.9 eV, or about 7.3 eV to about 7.8 eV. By having relatively deep HOMO energy levels as described herein, the inorganic nanoparticles (or the first charge-assisted layer 14) can be configured to effectively block the reverse injection of the second charge carriers (minor charge carriers, such as holes) from the light-emitting layer 13, and thus improve the stability of the quantum dot device 10.

[0113] The inorganic nanoparticles may include materials that satisfy the aforementioned energy levels, such as metal oxide nanoparticles of 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), barium (Ba), or combinations thereof.

[0114] For example, the inorganic nanoparticles may include metal oxide nanoparticles containing zinc (Zn), for example, denoted as Zn. 1-x Q x Metal oxide nanoparticles of O (0≤x<0.5). Q may include one or more metals 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.

[0115] For example, Q may include magnesium (Mg).

[0116] For example, x can satisfy the following ranges: 0.01≤x≤0.4, 0.01≤x≤0.3, or 0.01≤x≤0.2.

[0117] In addition to the aforementioned inorganic nanoparticles, the first charge-assisted layer 14 may further include alkali metals, alkali metal compounds, or combinations thereof. The alkali metals, alkali metal compounds, or combinations thereof may be included in the form of a mixture with the aforementioned inorganic nanoparticles, and may be included in a limited amount in the first charge-assisted layer 14 to effectively improve the electrical properties of the first charge-assisted layer 14.

[0118] The alkali metal, alkali metal compound, or combination thereof may be included, for example, in the form of an alkali metal cation, an alkali metal cation derived from an alkali metal compound, or a combination thereof. The alkali metal compound may be a compound comprising an alkali metal, such as an alkali metal carbonate, an alkali metal phosphate, an alkali metal vanadate, an alkali metal azide, an alkali metal nitride, or a combination thereof.

[0119] The alkali metal, or the alkali metal included in the alkali metal compound, may be, for example, lithium (Li), sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), francium (Fr), or combinations thereof. These lithium (Li), sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), or francium (Fr) may be included in the form of lithium cations, sodium cations, potassium cations, cesium cations, rubidium cations, or francium cations, respectively.

[0120] In addition to the alkali metal cations, the alkali metal compounds (e.g., alkali metal salts) may further include anions such as carbonate (CO3-) 2- ), phosphate (PO4) 3- ), vanadate (VO4) 3- ), azide (N3) - ), or nitrogen (N) 3- ).

[0121] For example, the alkali metal may be lithium (Li), sodium (Na), potassium (K), cesium (Cs), rubidium (Rb), francium (Fr), or combinations thereof, and the alkali metal compound may be cesium carbonate (Cs2CO3), cesium phosphate (Cs3PO4), cesium vanadate (Cs3VO4), cesium azide (CsN3), lithium carbonate (LiCO3), lithium nitride (Li3N), sodium carbonate (Na2CO3), potassium carbonate (K2CO3), rubidium carbonate (Rb2CO3), or combinations thereof, but is not limited thereto.

[0122] In the first charge-assisted layer 14, all alkali metals derived from the alkali metal, alkali metal compound, or combination thereof may be included in an amount less than that of the inorganic nanoparticles. For example, all alkali metals derived from the alkali metal, alkali metal compound, or combination thereof may be included in an amount based on about 0.1 volume percentage (volume%) to about 30 volume%, about 0.1 volume percentage to about 25 volume%, about 0.1 volume percentage to about 20 volume%, about 0.5 volume percentage to about 18 volume%, about 1 volume percentage to about 15 volume%, or about 3 volume percentage to about 15 volume percentage of the first charge-assisted layer 14. For example, all alkali metals derived from the alkali metal, alkali metal compound, or combination thereof may be included in an amount less than about 0.5 atomic percentage (atomic%) of the total number of atoms included in the first charge-assisted layer 14.

[0123] The thickness of the first charge-assisted layer 14 may be less than or equal to about 80 nm, for example, about 2 nm to about 80 nm, about 5 nm to about 80 nm, about 10 nm to about 60 nm, about 15 nm to about 50 nm, or about 10 nm to about 20 nm.

[0124] The buffer layer 15 is located between the light-emitting layer 13 and the first charge-assisted layer 14 to prevent the deterioration of electrical properties that may occur at the interface between the light-emitting layer 13 and the first charge-assisted layer 14.

[0125] For example, the buffer layer 15 can effectively extract excess charge carriers that have not yet recombinated in the light-emitting layer 13 and can effectively prevent the generation of non-emitting excitons that are abnormally recombinated at the interface (boundary) of the light-emitting layer 13 rather than inside the light-emitting layer 13 and cannot participate in light emission, and can prevent the deterioration of the interface of the light-emitting layer 13.

[0126] As described herein, the first charge-assisted layer 14 enhances the transport of the first charge carriers (primary charge carriers, such as electrons) from the second electrode 12 to the light-emitting layer 13, while blocking the reverse injection of the second charge carriers (minor charge carriers, such as holes) from the light-emitting layer 13 to the second electrode 12. To block the reverse injection of these second charge carriers (minor charge carriers, such as holes), as described herein, the HOMO level of the first charge-assisted layer 14 may be deeper than the HOMO level of the light-emitting layer 13.

[0127] If the buffer layer 15 is absent, the luminescent layer 13 and the first charge-assisted layer 14 can contact each other, and excess second charge carriers (minor charge carriers, such as holes) that do not recombine in the luminescent layer 13 can be blocked by the first charge-assisted layer 14 (e.g., a deep HOMO level of the first charge-assisted layer 14) and accumulate at the interface between the luminescent layer 13 and the first charge-assisted layer 14. Furthermore, the excess second charge carriers (minor charge carriers, such as holes) accumulated at this interface can aberrantly recombine with first charge carriers (major charge carriers, such as electrons) moving from the second electrode 12 to the luminescent layer 13 at this interface to generate non-emitting excitons. Such an excess of secondary charge carriers (minor charge carriers, such as holes) and non-emitting excitons can accumulate at the interface between the light-emitting layer 13 and the first charge-assisted layer 14, thereby deteriorating the interface of the light-emitting layer 13 and becoming a leakage (loss) pathway for the quantum dot device 10, ultimately deteriorating the lifetime and electrical characteristics of the quantum dot device 10.

[0128] The buffer layer 15 is located between the light-emitting layer 13 and the first charge-assisted layer 14, so that the light-emitting layer 13 and the first charge-assisted layer 14 do not directly contact each other, and can increase the extraction of excess second charge carriers (minor charge carriers, such as holes) from the light-emitting layer 13 to prevent the accumulation of excess second charge carriers (minor charge carriers, such as holes) at the interface of the light-emitting layer 13 and to prevent the generation of non-emitting excitons at the interface.

[0129] For example, buffer layer 15 may be a secondary charge carrier trapping layer capable of trapping excess secondary charge carriers (minor charge carriers, such as holes). For example, the number of trapping sites in buffer layer 15 may be controlled by the amount of secondary charge-assisted material (e.g., hole-extraction material) described herein.

[0130] As described herein, the first charge-assisted layer 14 can be configured to block the reverse injection of the second charge carriers (minor charge carriers, such as holes). Excess second charge carriers (minor charge carriers, such as holes) extracted into the buffer layer 15 can be blocked by the first charge-assisted layer 14 and confined in the buffer layer 15. The buffer layer 15 can replace the interface of the light-emitting layer 13 as an accumulation region of excess second charge carriers (minor charge carriers, such as holes), thereby effectively preventing the deterioration of the interface of the light-emitting layer 13.

[0131] For example, the buffer layer 15 may be in contact with the light-emitting layer 13.

[0132] For example, the buffer layer 15 may be in contact with the first charge-assisted layer 14.

[0133] For example, one surface of the buffer layer 15 may be in contact with the light-emitting layer 13, and the other surface of the buffer layer 15 may be in contact with the first charge-assisted layer 14.

[0134] For example, the buffer layer 15 may include a first charge-assist material configured to enhance the transport of the first charge carriers (primary charge carriers, such as electrons) from the second electrode 12 to the light-emitting layer 13, and a second charge-assist material configured to enhance the extraction of the second charge carriers (minor charge carriers, such as holes). The first and second charge-assist materials may be blended in the buffer layer 15. The first charge-assist material provides a transport path for the first charge carriers (primary charge carriers, such as electrons) in the buffer layer 15, and the second charge-assist material provides an extraction path for the second charge carriers (minor charge carriers, such as holes) within the buffer layer 15.

[0135] For example, when the first charge carrier is an electron and the second charge carrier is a hole, the HOMO level of the second charge-assisted material may be shallower than the HOMO level of the first charge-assisted material. For example, the HOMO energy level of the second charge-assisted material may be shallower than the HOMO energy level of the first charge-assisted material by greater than or equal to about 0.1 eV, greater than or equal to about 0.2 eV, greater than or equal to about 0.4 eV, greater than or equal to about 0.5 eV, greater than or equal to about 0.7 eV, or greater than or equal to about 1.0 eV, about 0.1 eV to about 5.0 eV, about 0.1 eV to about 4.5 eV, about 0.1 eV to about 4.0 eV, about 0.1 eV to about 3.5 eV, about 0.1 eV to about 3.0 eV, about 0.2 eV to about 5.0 eV, about 0.2 eV to about 4.5 eV, about 0.2 eV to about 4.0 eV, about 0.2 eV to about 3.5 eV, about 0.2 eV to about 3.0 eV, or about 0.4 eV to about 5.0 eV. Approximately 0.4 eV to approximately 4.5 eV, approximately 0.4 eV to approximately 4.0 eV, approximately 0.4 eV to approximately 3.5 eV, approximately 0.4 eV to approximately 3.0 eV, approximately 0.5 eV to approximately 5.0 eV, approximately 0.5 eV to approximately 4.5 eV, approximately 0.5 eV to approximately 4.0 eV, approximately 0.5 eV to approximately 3.5 eV, approximately 0.5 eV to approximately 3.0 eV, approximately 0.7 eV- Approximately 5.0 eV, approximately 0.7 eV to approximately 4.5 eV, approximately 0.7 eV to approximately 4.0 eV, approximately 0.7 eV to approximately 3.5 eV, approximately 0.7 eV to approximately 3.0 eV, approximately 1.0 eV to approximately 5.0 eV, approximately 1.0 eV to approximately 4.5 eV, approximately 1.0 eV to approximately 4.0 eV, approximately 1.0 eV to approximately 3.5 eV, or approximately 1.0 eV to approximately 3.0 eV.

[0136] For example, when the first charge carrier is a hole and the second charge carrier is an electron, the LUMO energy level of the second charge-assisted material can be deeper than the LUMO energy level of the first charge-assisted material. For example, the LUMO energy level of the second charge-assisted material can be deeper than the LUMO energy level of the first charge-assisted material by greater than or equal to about 0.1 eV, greater than or equal to about 0.2 eV, greater than or equal to about 0.4 eV, greater than or equal to about 0.5 eV, greater than or equal to about 0.7 eV, or greater than or equal to about 1.0 eV, for example, about 0.1 eV to about 3.0 eV, about 0.2 eV to about 3.0 eV, about 0.4 eV to about 3.0 eV, about 0.5 eV to about 3.0 eV, about 0.7 eV to about 3.0 eV, or about 1.0 eV to about 3.0 eV.

[0137] For example, when the first charge carrier is an electron and the second charge carrier is a hole, the first charge-assisting material can be an electron transport material and the second charge-assisting material can be a hole extraction material. The first charge-assisting material can be the same as or different from the charge transport material included in the first charge-assisting layer 14.

[0138] For example, the conductivity (e.g., hole conductivity) of the second charge carriers (minor charge carriers) of the second charge-assisted material (e.g., hole extraction material) may be greater than the conductivity (e.g., hole conductivity) of the second charge carriers (minor charge carriers) of the first charge-assisted material (e.g., electron transport material). For example, the conductivity (e.g., hole conductivity) of the second charge carriers (minor charge carriers) of the second charge-assisted material (e.g., hole extraction material) may be approximately 1.01 to approximately 10 times that of the second charge carriers (minor charge carriers) of the first charge-assisted material (e.g., electron transport material). 4 1.2 times - approximately 10 times 4 1.5 times - approximately 10 times 4 10 times, approximately 2 times - approximately 10 times 4 10 times, approximately 5 times - approximately 10 times 4 Times, or about 10 times - about 10 4 times.

[0139] For example, the charge mobility (e.g., electron mobility) of the first charge-assisted material (e.g., electron transport material) may be greater than or equal to about 100 square centimeters per volt-second (cm²). 2 / Vs), or approximately 100cm 2 / Vs-approx. 1,000cm 2 / Vs. For example, the charge mobility (e.g., hole mobility) of the second charge-assisted material (e.g., hole extraction material) may be greater than or equal to about 10. -5 cm 2 / Vs, or approximately 10 -5 cm 2 / Vs-approx. 10 -4 cm 2 / Vs.

[0140] The first charge-assisting material (e.g., an electron transport material) may include, for example, an n-type non-polymer material (e.g., an n-type non-polymer organic material), an n-type polymer, an n-type inorganic material, an n-type organic-inorganic material, or a combination thereof. For example, the first charge-assisting material may include inorganic nanoparticles, such as n-type inorganic nanoparticles. For example, the first charge-assisting material may be the same as or different from the charge transport material included in the first charge-assisting layer 14, and may include, for example, the same or different n-type inorganic nanoparticles. For example, the first charge-assisting material may include metal oxide nanoparticles containing zinc (Zn), for example, nanoparticles made of Zn... 1-x Q x Metal oxide nanoparticles represented by O (0≤x<0.5, e.g., 0.01≤x≤0.4, 0.01≤x≤0.3, or 0.01≤x≤0.2). Q is one or more metals 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. For example, the first charge-assisting material may be the same as or different from the electron transport material included in the first charge-assisting layer 14.

[0141] The second charge-assisted material (e.g., a hole-extraction material) may include, for example, p-type non-polymeric materials (e.g., p-type non-polymeric organic materials), p-type polymers, p-type inorganic materials, p-type organic-inorganic materials, or combinations thereof. For example, the second charge-assisted material may include N,N,N',N'-tetratetra(4-methoxyphenyl)-benzidine (TPD), N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), 4,4',4"-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA), 4,4',4"-tris(N-carbazolyl)-triphenylamine (TCTA), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N2,N7-bis(naphthyl-1-yl)-9,9-dioctyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (NPB), 2,7-bis(carbazole-9-yl)-9,9-spirodifluorene (Spiro-2CBP), 2,2',7,7'-tetra(N,N-di-p-tolyl)amino-9, 9-Spiro-difluorene (Spiro-TTB), 2,2',7,7'-tetra(N,N-diphenylamino)-9,9-spiro-difluorene (Spiro-TAD), 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), 4,4',4”-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), 1,3,5-tris(4-diphenylaminophenyl)benzene (TDAPB), poly( 9,9-Dioctyl-fluorene-co-N-(4-Butylphenyl)-diphenylamine (TFB), polyarylamines (polyarylamines), poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS), polyaniline, polypyrrole, Spiro-PMATD, triphenylbismuth dichloride (TPBC), H-111, formula Compounds (OMe TPA-FA), 2TPA-2-DP (where TPA is 4,4'-((1E,1'E,3E,3'E)-[1,1'-biphenyl]-4,4'-diylbis(but-1,3-diene-4,1-diyl)); DP = bis(N,N-di-p-tolylaniline); n = 2), pyridine diimide (PDI), poly(triarylamine) (PTAA), poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[3-(5-carboxypentyl)thiophene-2,5-diyl] (P3CPenT), poly[2,6-(4, 4-Bis-(2-ethylhexyl)-4H-cyclopentano[2,1-b;3,4-b']dithiophene)-alternating-4,7-(2,1,3-benzothiadiazole)](PCPDT-t), poly(2,3-dihydrothiopheno[3,4-b][1,4]dioxane-5,7-diyl) (PEDOT-S), polyferric sulfate (PFS), poly[2,6-(4,4-bis-butyrylate potassium-4H-cyclopentano-[2,1-b;3,4-b']dithiophene)-alternating-4,7-(2,1,3-benzothiadiazole)](CPE-K), formula Compounds including (CPEPh-Na), sodium phenyl (PhNa-IT), sulfonated poly(diphenylamine) (SPDPA), phlorofucofuroeckol (p-PFF-O), poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopentano[2,1-b;3,4-b']dithiophene)-alternate-4,7-(2,1,3-benzothiadiazole)] (CPE-PCPDT-K), poly[(9,9-bis(4-sulfonate sodium butyl)fluorene-alternate-phenylene)-random-(4,7-di-2-thienyl-2,1,3-benzothiadiazole-alternate-phenylene)] (PSFP-DTBTP), CuI, Cu2O, CuO, CuS, NiO x , CuGaO2, CuPc, CuSCN, MoO x MoS2, VO x CoO x Graphene oxide, or combinations thereof, but not limited to these.

[0142] For example, the second charge-assisted material (e.g., a hole-extraction material) may be inorganic nanoparticles, such as inorganic nanoparticles including the aforementioned p-type inorganic material. For example, at least one of the first charge-assisted material (e.g., an electron transport material) included in the buffer layer 15, the second charge-assisted material (e.g., a hole-extraction material) included in the buffer layer 15, and the electron transport material included in the first charge-assisted layer 14 may be inorganic nanoparticles.

[0143] The content of the second charge-assisting material can be determined taking into account the number of trapping sites in the buffer layer 15, and the number of trapping sites in the buffer layer 15 can increase as the content of the second charge-assisting material increases. For example, in the buffer layer 15, the amount of the second charge-assisting material can be less than the amount of the first charge-assisting material. For example, in the buffer layer 15, based on the total amount of the first charge-assisting material and the second charge-assisting material, the second charge-assisting material can be included in the following amounts: less than or equal to about 40 wt%, less than or equal to about 30 wt%, less than or equal to about 20 wt%, less than or equal to about 15 wt%, less than or equal to about 12 wt%, less than or equal to about 10 wt%, less than or equal to about 8 wt%, or less than or equal to about 6 wt%, for example, about 0.1 wt% to about 40 wt%, about 0.1 wt% to about 30 wt%, about 0.1 wt%. % by weight - about 20% by weight, about 0.1% by weight - about 15% by weight, about 0.1% by weight - about 12% by weight, about 0.1% by weight - about 10% by weight, about 0.1% by weight - about 8% by weight, about 0.1% by weight - about 6% by weight, about 1% by weight - about 40% by weight, about 1% by weight - about 30% by weight, about 1% by weight - about 20% by weight, about 1% by weight - about 15% by weight, about 1% by weight - about 12% by weight, about 1% by weight - about 10% by weight, about 1% by weight - about 8% by weight, or about 1% by weight - about 6% by weight.

[0144] By including the aforementioned second charge-assisted material, the buffer layer 15 may have a second charge carrier (minor charge carrier) conductivity (e.g., hole conductivity) that is greater than that of the second charge carrier (minor charge carrier) conductivity (e.g., hole conductivity) of the first charge-assisted layer 14. For example, the second charge carrier (minor charge carrier, e.g., hole) conductivity (e.g., hole conductivity) of the buffer layer 15 may be approximately 1.01 to approximately 10 times that of the second charge carrier (minor charge carrier, e.g., hole conductivity) of the first charge-assisted layer 14. 4 1.2 times - approximately 10 times 4 1.5 times - approximately 10 times 4 10 times, approximately 2 times - approximately 10 times 4 10 times, approximately 5 times - approximately 10 times 4 Times, or about 10 times - about 10 4 The conductivity (e.g., hole conductivity) of the second charge carrier (minor charge carrier) can be measured and compared using conductive atomic force microscopy (C-AFM).

[0145] By including the aforementioned second charge-assisting material, the buffer layer 15 may have a higher conductivity of second charge carriers (minor charge carriers, such as holes) than the first charge-assisting layer 14 and the light-emitting layer 13 (e.g., hole conductivity). For example, the conductivity of second charge carriers (minor charge carriers, such as holes) in the buffer layer 15 may be approximately 1.01 times to approximately 10 times that of the conductivity of second charge carriers (minor charge carriers, such as holes) in the first charge-assisting layer 14 (e.g., hole conductivity) and the conductivity of second charge carriers (minor charge carriers, such as holes) in the light-emitting layer 13 (e.g., hole conductivity). 4 1.2 times - approximately 10 times 4 1.5 times - approximately 10 times 4 10 times, approximately 2 times - approximately 10 times 4 10 times, approximately 5 times - approximately 10 times 4 Times, or about 10 times - about 10 4 Therefore, when the conductivity is measured along the cross-section of the quantum dot device 10 using a conductive atomic force microscope (C-AFM), a peak can be observed in the buffer layer 15.

[0146] The thickness of the buffer layer 15 may be the same as or thinner than the thickness of the first charge-assisted layer 14. The thickness of the buffer layer 15 may be, for example, less than or equal to about 20 nm, for example, less than or equal to about 15 nm, less than or equal to about 12 nm, less than or equal to about 10 nm, less than or equal to about 8 nm, less than or equal to about 7 nm, or less than or equal to about 5 nm, for example, about 1 nm to about 20 nm, about 1 nm to about 15 nm, about 1 nm to about 12 nm, about 1 nm to about 10 nm, about 1 nm to about 8 nm, about 1 nm to about 7 nm, or about 1 nm to about 5 nm.

[0147] A second charge-assisted layer 16 is located between the first electrode 11 and the light-emitting layer 13. The second charge-assisted layer 16 may be a functional layer for improving the electrical performance between the first electrode 11 and the light-emitting layer 13, and may increase the transport of the second charge carriers from the first electrode 11 to the light-emitting layer 13. The second charge carriers may be the dominant charge carriers between the first electrode 11 and the light-emitting layer 13. For example, when the first electrode 11 is an anode, the second charge carriers may be holes, and the second charge-assisted layer 16 may be a hole-assisted layer, such as a hole transport layer, a hole injection layer, an electron blocking layer, or a combination thereof. For example, when the first electrode 11 is a cathode, the second charge carriers are electrons, and the second charge-assisted layer 16 may be an electron-assisted layer, such as an electron transport layer, an electron injection layer, a hole blocking layer, or a combination thereof. The second charge-assisted layer 16 may comprise one layer or two or more layers.

[0148] For example, the first electrode 11 can be an anode and the second electrode 12 can be a cathode. The first charge-assisted layer 14 can be an electron-assisted layer, such as an electron transport layer, an electron injection layer, a hole blocking layer, or a combination thereof, and the second charge-assisted layer 16 can be a hole-assisted layer, such as a hole transport layer, a hole injection layer, an electron blocking layer, or a combination thereof.

[0149] The HOMO level of the second charge-assisted layer 16 can have a relatively deep HOMO level to match the HOMO level of the emitting layer 13. Therefore, the mobility of the second charge carriers (e.g., holes) transferred from the second charge-assisted layer 16 to the emitting layer 13 can be improved.

[0150] The HOMO energy level of the second charge-assisted layer 16 may be equal to or smaller than the HOMO energy level of the luminescent layer 13 by a value in the range of less than or equal to about 1.0 eV. For example, the difference between the HOMO energy levels of the luminescent layer 13 and the second charge-assisted layer 16 may be about 0 eV to about 1.0 eV, 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.

[0151] The HOMO level of the second charge-assisted layer 16 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.

[0152] For example, the HOMO energy levels of the second charge-assisted layer 16 can be approximately 5.0 eV–approximately 7.0 eV, approximately 5.2 eV–approximately 6.8 eV, approximately 5.4 eV–approximately 6.8 eV, approximately 5.4 eV–approximately 6.7 eV, approximately 5.4 eV–approximately 6.5 eV, approximately 5.4 eV–approximately 6.3 eV, approximately 5.4 eV–approximately 6.2 eV, approximately 5.4 eV–approximately 6.1 eV, approximately 5.6 eV–approximately 7.0 eV, approximately 5.6 eV–approximately 6.8 eV, and approximately 5.6 eV. eV - about 6.7 eV, about 5.6 eV - about 6.5 eV, about 5.6 eV - about 6.3 eV, about 5.6 eV - about 6.2 eV, about 5.6 eV - about 6.1 eV, about 5.8 eV - about 7.0 eV, about 5.8 eV - about 6.8 eV, about 5.8 eV - about 6.7 eV, about 5.8 eV - about 6.5 eV, about 5.8 eV - about 6.3 eV, about 5.8 eV - about 6.2 eV, or about 5.8 eV - about 6.1 eV.

[0153] The second charge-assisted layer 16 may include one or more hole transport materials, and the hole transport material may include, for example, N,N,N',N'-tetratetra(4-methoxyphenyl)-benzidine (TPD), N,N'-di(1-naphthyl)-N,N'-diphenyl-(1,1'-biphenyl)-4,4'-diamine (NPD), 4,4',4”-tris[phenyl(m-tolyl)amino]triphenylamine (m-MTDATA), 4 4',4”-Tris(N-carbazolyl)-triphenylamine (TCTA), 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N2,N7-bis(naphthyl-1-yl)-9,9-dioctyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (NPB), 2,7-bis(carbazolyl)-9,9-spirodifluorene (Spiro-2CBP), 2,2',7,7'-tetra(N,N) 2,2',7,7'-Tetra(N,N-diphenylamino)-9,9-spirodifluorene (Spiro-TTB), 2,2',7,7'-Tetra(N,N-diphenylamino)-9,9-spirodifluorene (Spiro-TAD), 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP), 4,4',4'-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA), 1,3,5-tris(4-diphenylaminophenyl)benzene ( TDAPB), poly(9,9-dioctyl-fluorene-co-N-(4-butylphenyl)-diphenylamine) (TFB), polyarylamine, poly(N-vinylcarbazole), poly(3,4-ethylenedioxythiophene) (PEDOT), poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS), polyaniline, polypyrrole, Spiro-PMATD, triphenylbismuth dichloride (TPBC), H-111, OMe TPA-FA, 2TPA-2-DP, pyridine diimide (PDI), poly(triarylamine) (PTAA), poly(3-hexylthiophene-2,5-diyl) (P3HT), poly[3-(5-carboxypentyl)thiophene-2,5-diyl] (P3CPenT), poly[2,6-(4,4-bis-(2-ethylhexyl)-4H-cyclopento[2,1-b;3,4-b']dithiophene)-alternating-4,7(2 [1,3-benzothiadiazole](PCPDT-t), poly(2,3-dihydrothiophene[3,4-b][1,4]dioxane-5,7-diyl)(PEDOT-S), polyferric sulfate (PFS), poly[2,6-(4,4-bis-butyrate potassium-4H-cyclopenta-[2,1-b;3,4-b']-dithiophene)-alternating-4,7-(2,1,3-benzothiadiazole)](CPE-K), formula Compounds including (CPEPh-Na), sodium phenyl (PhNa-IT), sulfonated poly(diphenylamine) (SPDPA), sakiran laminarin (p-PFF-O), poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopentano[2,1-b;3,4-b']dithiophene)-alternate-4,7-(2,1,3-benzothiadiazole)] (CPE-PCPDT-K), poly[(9,9-bis(4-sulfonate sodium butyl)fluorene-alternate-phenylene)-random-(4,7-di-2-thienyl-2,1,3-benzothiadiazole-alternate-phenylene)] (PSFP-DTBTP), CuI, Cu2O, CuO, CuS, NiO x , CuGaO2, CuPc, CuSCN, MoO x MoS2, VO x CoO x Graphene oxide, or combinations thereof, but not limited thereto. For example, the hole transport material included in the second charge-assisted layer 16 may be the same as or different from the hole extraction material included in the buffer layer 15.

[0154] The method for manufacturing the aforementioned quantum dot device 10 includes forming a first electrode 11, forming a second charge-assisted layer 16, forming a light-emitting layer 13, forming a buffer layer 15, forming a first charge-assisted layer 14, and forming a second electrode 12 on a substrate (not shown).

[0155] The light-emitting layer 13, the first and second charge-assisted layers 14 and 16, the buffer layer 15, or combinations thereof may be formed by solution processes such as spin coating, slot coating, inkjet printing, nozzle printing, jetting, doctor blade coating, or combinations thereof, but are not limited thereto.

[0156] At least a portion of the process for forming the light-emitting layer 13, the first and second charge-assisted layers 14 and 16, the buffer layer 15, or combinations thereof may further include, optionally, drying, heat treatment, or combinations thereof after the solution process, and the heat treatment may be performed, for example, at about 50°C to about 300°C for about 1 minute to about 10 hours, but this disclosure is not limited thereto.

[0157] The aforementioned quantum dot device 10 can be applied to a variety of electronic devices, such as display devices or lighting devices. For example, the aforementioned quantum dot device 10 can be applied to electronic devices that require light emission, such as display devices like televisions (TVs), monitors, computers, mobile phones, etc., or lighting devices like light sources.

[0158] The embodiments are described in more detail below with reference to examples. However, these embodiments are exemplary, and the scope of the claims is not limited thereto.

[0159] Synthesis of quantum dot dispersions

[0160] Synthesis Example 1: Synthesis of Quantum Dot 1 that Emits Blue Light

[0161] (1) Synthesis of ZnTeSe core quantum dot dispersion

[0162] Selenium (Se) and tellurium (Te) were dispersed in trioctylphosphine (TOP) to obtain a 2 M concentration (mol / L (M)) Se / TOP stock solution (stock solution) and a 0.1 M Te / TOP stock solution.

[0163] 0.125 mmol of zinc acetate, 0.25 mmol of oleic acid, 0.25 mmol of hexadecylamine, and 10 mL of trioctylamine were added to the reactor, which was then heated at 120 °C under vacuum. After 1 hour, the atmosphere in the reactor was changed to nitrogen.

[0164] After heating the reactor to 240°C, the Se / TOP stock solution and the Te / TOP stock solution were rapidly injected into it at a Te:Se molar ratio of 1:25. The reaction solution was heated to 300°C and held for 30 minutes, then rapidly cooled to room temperature. Acetone was added, and the precipitate obtained by centrifugation was dispersed in toluene to obtain a ZnTeSe core quantum dot dispersion.

[0165] (2) Synthesis of ZnTeSe core / ZnSeS shell quantum dot dispersions

[0166] Trioctylamine was added to a 10 mL flask. Subsequently, 0.6 mmol of zinc acetate and 1.2 mmol of oleic acid were added, followed by vacuum treatment at 120 °C for 10 min. The flask was then purged with nitrogen (N2), and the ZnTeSe core quantum dot dispersion was rapidly injected, along with the 2M Se / TOP stock solution at a Se:S molar ratio of 1.2:2.8 and the 1M S / TOP stock solution obtained by dispersing sulfur (S) in trioctylphosphine (TOP). The mixture was then heated to 340 °C for reaction. Upon completion of the reaction, the reactor was cooled, and the obtained nanocrystals were centrifuged with ethanol and then dispersed in toluene to obtain a ZnTeSe core / ZnSeS shell quantum dot dispersion.

[0167] Synthesis Example 2: Synthesis of Quantum Dot 2 that Emits Blue Light

[0168] Zinc chloride was dissolved in ethanol to obtain a zinc chloride solution with a concentration of 10 wt%. 0.01 mL of the zinc chloride solution was added to the ZnTeSe core / ZnSeS shell quantum dot dispersion according to Synthesis Example 1, and the mixture was stirred at 60 °C for 30 min to carry out a surface exchange reaction. After the reaction, ethanol was added to induce precipitation, followed by centrifugation, and this process was repeated several times to obtain a halogenated ZnTeSe core / ZnSeS shell quantum dot dispersion.

[0169] Synthesis of Inorganic Nanoparticles

[0170] Synthesis Example 3

[0171] 0.93 mmol of magnesium acetate tetrahydrate, 8.07 mmol of zinc acetate dihydrate, and 90 mL of dimethyl sulfoxide were added to the reactor and heated in air at 60 °C. Subsequently, 15 mmol of tetramethylammonium hydroxide pentahydrate was dissolved in 30 mL of ethanol and then added dropwise to the reactor at a rate of 3 mL / min. After stirring the mixture for 1 hour, the obtained Zn... 0.85 Mg 0.15 O nanoparticles and ethyl acetate were centrifuged at a volume ratio of 1:9 and dispersed in ethanol at a concentration of 1% by weight to obtain Zn. 0.85 Mg 0.15 O nanoparticle dispersion (9.6 mg / ml). The Zn content was measured using a UT F30 Tecnai electron microscope. 0.85 Mg 0.15 The O nanoparticles have an average particle diameter of approximately 3.0 nanometers (nm).

[0172] Preparation of dispersions for electron-assisted layers (first charge-assisted layers)

[0173] Preparation Example 1

[0174] 0.06 mg of Rb₂CO₃ was added to 6 mL of ethanol and stirred overnight (6 hours or longer) to prepare an Rb₂CO₃ solution (concentration 0.01 mg / mL). Subsequently, the Zn obtained in Synthesis Example 3 was... 0.85 Mg 0.15 The O nanoparticle dispersion and the Rb2CO3 solution were mixed at a volume ratio of 5:1 to prepare a dispersion for use in an electronic auxiliary layer.

[0175] Preparation of dispersions for buffer layers

[0176] Preparation Example 2

[0177] N2,N7-bis(naphthyl-1-yl)-9,9-dioctyl-N2,N7-diphenyl-9H-fluorene-2,7-diamine (NPB, cavitation extractant) was dissolved in ethanol at a concentration of 2 mg / mL to prepare an NPB solution. Subsequently, 3.73 mL of Zn according to synthesis example 3 was added... 0.85 Mg 0.15 The O nanoparticle dispersion and 0.27 mL of the NPB solution were mixed to prepare a dispersion for a buffer layer. In the dispersion for the buffer layer, the NPB weight concentration was 1.5% wt%, based on Zn. 0.85 Mg 0.15 The total amount of O nanoparticles and NPB.

[0178] Preparation Example 3

[0179] The dispersion for the buffer layer was prepared according to the same method as in Preparation Example 2, except that: 3.48 mL of Zn according to Synthesis Example 3 was added. 0.85 Mg 0.15 The O nanoparticle dispersion was mixed with 0.52 mL of the NPB solution. In the dispersion used for the buffer layer, the NPB concentration was 3% by weight, based on Zn. 0.85 Mg 0.15 The total amount of O nanoparticles and NPB.

[0180] Preparation Example 4

[0181] The dispersion for the buffer layer was prepared according to the same method as in Preparation Example 2, except that: 3.19 mL of Zn according to Synthesis Example 3 was added. 0.85 Mg 0.15 The O nanoparticle dispersion was mixed with 0.81 mL of the NPB solution. In the dispersion used for the buffer layer, the NPB concentration was 5% by weight, based on Zn. 0.85 Mg 0.15 The total amount of O nanoparticles and NPB.

[0182] Preparation Example 5

[0183] The dispersion for the buffer layer was prepared according to the same method as in Preparation Example 2, except that: 3.06 mL of Zn according to Synthesis Example 3 was added. 0.85 Mg 0.15 The O nanoparticle dispersion was mixed with 0.94 mL of the NPB solution. In the dispersion used for the buffer layer, the NPB concentration was 6% by weight, based on Zn. 0.85 Mg 0.15 The total amount of O nanoparticles and NPB.

[0184] Thin film manufacturing

[0185] Thin film samples were formed to evaluate the energy levels of the synthesized and prepared materials.

[0186] Preparation Example 6

[0187] The dispersion for the electronic auxiliary layer prepared according to Example 1 was spin-coated onto a Si substrate and then heat-treated at 80°C for 30 minutes to form a 30 nm thick film.

[0188] Preparation Example 7

[0189] The solution prepared by dissolving the hole extraction material NPB used in Preparation Examples 2-5 in ethanol at a concentration of 3% by weight was spin-coated onto a Si substrate and then heat-treated at 80°C for 30 minutes to form a 30 nm thick film.

[0190] Evaluation I

[0191] The highest occupied molecular orbital (HOMO) levels of the thin films prepared according to Examples 6 and 7 were evaluated by ultraviolet (UV) photoelectron spectroscopy (UPS, Versaprobe, Physical Electronics, Inc.). The lowest unoccupied molecular orbital (LUMO) levels were calculated using the band gap energies obtained from the absorption peaks of the spectra analyzed by the UPS and the HOMO levels.

[0192] The results are shown in Table 1.

[0193] Table 1

[0194] Preparation Example 6 7.40 3.41 Preparation Example 7 5.2 2.4

[0195] Fabrication of a quantum dot device I that emits blue light

[0196] Example 1

[0197] A glass substrate with a 100 nm thick indium tin oxide (ITO) layer (work function (WF): 4.8 eV, first electrode) was surface-treated with UV-ozone for 15 minutes, then spin-coated with a poly(3,4-ethylenedioxythiophene):polysulfonated styrene (PEDOT:PSS) solution (HCStarks), and heat-treated at 150 °C for 10 minutes in air atmosphere, and then heat-treated again at 150 °C for 30 minutes in N2 atmosphere to form a 30 nm thick lower hole transport layer (HOMO: 5.3 eV, LUMO: 2.7 eV). Subsequently, a poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine] solution (TFB) (Sumitomo Corp.) was spin-coated onto the lower hole-assist layer and heat-treated at 150°C for 30 minutes to form a 25 nm thick upper hole-assist layer (HOMO: 5.6 eV, LUMO: 2.69 eV). Then, a halogenated ZnTeSe / ZnSeS core-shell quantum dot dispersion (peak emission wavelength: 453 nm) according to Synthesis Example 2 was spin-coated onto the upper hole-assist layer and heat-treated at 80°C for 30 minutes to form a 25 nm thick upper hole-assist layer (HOMO: 5.6 eV, LUMO: 2.69 eV). A 28 nm thick quantum dot layer (light-emitting layer) (HOMO: 5.9 eV, LUMO: 3.2 eV) was formed. Subsequently, a dispersion for a buffer layer according to Preparation Example 2 was spin-coated onto the quantum dot layer and heat-treated at 80°C for 30 minutes to form a 5 nm thick buffer layer. Then, a dispersion for an electron-assisted layer according to Preparation Example 1 was spin-coated onto the buffer layer and heat-treated at 80°C for 30 minutes to form a 15 nm thick electron-assisted layer. Finally, aluminum (Al) was vacuum-deposited onto the electron-assisted layer to form a 100 nm thick second electrode (WF: 4.2 eV), thereby fabricating the quantum dot device.

[0198] Example 2

[0199] The quantum dot device was fabricated according to the same method as in Example 1, except that the buffer layer was formed by using the dispersion for the buffer layer according to Example 3 instead of the dispersion for the buffer layer according to Example 2.

[0200] Example 3

[0201] The quantum dot device was fabricated according to the same method as in Example 1, except that the buffer layer was formed by using the dispersion for the buffer layer according to Example 4 instead of the dispersion for the buffer layer according to Example 2.

[0202] Comparative Example 1

[0203] The quantum dot device is manufactured according to the same method as in Example 1, except that the buffer layer is not formed.

[0204] Evaluation II

[0205] The lifetime characteristics of the quantum dot devices in Examples 1-3 and Comparative Example 1 were evaluated.

[0206] The lifetime characteristics were evaluated by measuring the decrease in brightness from the initial brightness when the injected current met the condition that the quantum dot device exhibited a brightness of 650 nits (candela / m²), and T was evaluated relatively by measuring the time it took for the quantum dot device to exhibit 90% of its initial brightness and using the corresponding time of Comparative Example 1 as a reference. 90 .

[0207] The results are shown in Table 2.

[0208] Table 2

[0209] Example 1 1.23 Example 2 1.22 Example 3 1.64 Comparative Example 1 1.00 (ref.)

[0210] Referring to Table 2, the quantum dot devices of Examples 1-3 exhibit improved lifetime characteristics compared to the quantum dot device of Comparative Example 1.

[0211] Fabrication of a quantum dot device II that emits blue light

[0212] Example 4

[0213] A glass substrate with a 100 nm thick ITO layer (WF: 4.8 eV, first electrode) was surface-treated with UV-ozone for 15 minutes, then spin-coated with a PEDOT:PSS solution (HCStarks, Inc.), and heat-treated at 150 °C for 10 minutes in air, followed by a second heat treatment at 150 °C for 30 minutes in N2 atmosphere to form a 30 nm thick lower hole transport layer (HOMO: 5.3 eV, LUMO: 2.7 eV). Subsequently, a poly[(9,9-dioctylfluorene-2,7-diyl-co-(4,4'-(N-4-butylphenyl)diphenylamine] solution (TFB) (Sumitomo) was applied. Corp.) spin-coated the upper hole-assist layer onto the lower hole-assist layer and heat-treated at 150°C for 30 minutes to form a 25 nm thick upper hole-assist layer (HOMO: 5.6 eV, LUMO: 2.69 eV). On the upper hole-assist layer, a halogenated ZnTeSe / ZnSeS core-shell quantum dot dispersion (peak emission wavelength: 453 nm) according to Synthesis Example 2 was spin-coated and heat-treated at 80°C for 30 minutes to form a 28 nm thick lower quantum dot layer (lower emitting layer) (HOMO: 5.9 eV, LUMO: 3.2 eV). Subsequently, on the lower quantum dot layer, a halogenated ZnTeSe / ZnSeS core-shell quantum dot dispersion according to Synthesis Example 2 was spin-coated. A ZnTeSe / ZnSeS core-shell quantum dot dispersion was heat-treated at 80°C for 30 minutes to form a 13 nm thick upper quantum dot layer (upper light-emitting layer). On the upper quantum dot layer, a dispersion for a buffer layer according to Preparation Example 2 was spin-coated and heat-treated at 80°C for 30 minutes to form a 5 nm thick buffer layer. Subsequently, on the buffer layer, a dispersion for an electron-assisted layer according to Preparation Example 1 was spin-coated and heat-treated at 80°C for 30 minutes to form a 15 nm thick electron-assisted layer. On the electron-assisted layer, aluminum (Al) was vacuum-deposited to form a 100 nm thick second electrode (WF: 4.2 eV), thereby fabricating a quantum dot device.

[0214] Example 5

[0215] The quantum dot device is manufactured using the same method as in Example 4, except that a 10 nm thick electronic auxiliary layer is formed instead of the 15 nm thick electronic auxiliary layer.

[0216] Comparative Example 2

[0217] The quantum dot device was fabricated using the same method as in Example 4, except that the buffer layer was not formed.

[0218] Comparative Example 3

[0219] The quantum dot device was fabricated using the same method as in Example 5, except that the buffer layer was not formed.

[0220] Evaluation III

[0221] The lifetime characteristics of the quantum dot devices in Examples 4 and 5 and Comparative Examples 2 and 3 were evaluated.

[0222] The luminance characteristics were evaluated using a CS-2000 spectroradiometer (Konica Monolta).

[0223] The lifetime characteristics were evaluated by measuring the decrease in brightness from the initial brightness when the injected current met the condition that the quantum dot device exhibited a brightness of 650 nits. The lifetime characteristics were evaluated by measuring the time it took for the quantum dot device to exhibit 90% of its initial brightness, using the corresponding times of Comparative Examples 2 and 3 as references. 90 .

[0224] The results are shown in Table 3.

[0225] Table 3

[0226] Example 4 57743 1.20 Comparative Example 2 54870 1.00 (ref.) Example 5 56574 1.45 Comparative Example 3 51194 1.00 (ref.)

[0227] *Lum max (Cd / m 2 Maximum brightness (candela / m²) 2 ))

[0228] Referring to Table 3, compared with the quantum dot devices of Comparative Examples 2 and 3, the quantum dot devices of Examples 4 and 5 exhibit improved brightness and lifetime characteristics.

[0229] While this disclosure has been described with respect to exemplary embodiments currently considered practical, it will be understood that the invention is not limited to the disclosed embodiments. Rather, it is intended to cover various variations and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. Quantum dot devices, including First electrode and second electrode A light-emitting layer, comprising quantum dots, is located between the first electrode and the second electrode. A first charge-assisted layer is provided between the second electrode and the light-emitting layer, the first charge-assisted layer being configured to enhance the transport of first charge carriers from the second electrode to the light-emitting layer, and A buffer layer is provided between the light-emitting layer and the first charge-assisted layer, the buffer layer being configured to enhance the extraction of second charge carriers from the light-emitting layer. The first electrode is the anode, the second electrode is the cathode, the first charge carrier is an electron, and the second charge carrier is a hole. The highest occupied molecular orbital energy level of the first charge-assisted layer is deeper than that of the highest occupied molecular orbital energy level of the luminescent layer. The buffer layer includes a first charge-assist material configured to enhance the transport of the first charge carriers and a second charge-assist material configured to enhance the extraction of the second charge carriers. The highest occupied molecular orbital energy level of the second charge-assisted material is lower than that of the first charge-assisted material. The first charge-assisted material is a first electron transport material, and The second charge-assisted material is a hole extraction material.

2. The quantum dot device as claimed in claim 1, wherein... The first charge carrier is the dominant charge carrier between the second electrode and the light-emitting layer, and The second charge carrier is a secondary charge carrier between the second electrode and the light-emitting layer.

3. The quantum dot device of claim 1, wherein the buffer layer is in contact with the light-emitting layer.

4. The quantum dot device of claim 1, wherein the first charge-assisted layer and the buffer layer are in contact with each other.

5. The quantum dot device of claim 1, wherein the highest occupied molecular orbital energy level of the second charge-assisted material is 0.1 eV to 3.0 eV lower than the highest occupied molecular orbital energy level of the first charge-assisted material.

6. The quantum dot device as claimed in claim 1, wherein... The first charge-assisted material comprises n-type inorganic nanoparticles, and The second charge-assisted material includes p-type nonpolymer materials, p-type polymers, p-type inorganic materials, p-type organic-inorganic materials, or combinations thereof.

7. The quantum dot device of claim 1, wherein the conductivity of the second charge carriers of the second charge-assisted material is greater than the conductivity of the second charge carriers of the first charge-assisted material.

8. The quantum dot device of claim 1, wherein the first charge-assisted layer comprises a second electron transport material that is the same as or different from the first electron transport material.

9. The quantum dot device of claim 1, wherein the second charge-assist material is present in the buffer layer in a smaller amount than the first charge-assist material.

10. The quantum dot device of claim 9, wherein in the buffer layer, the second charge-assist material is present in an amount of 0.1 wt% to 15 wt% based on the total amount of the first charge-assist material and the second charge-assist material.

11. The quantum dot device of claim 1, wherein the thickness of the buffer layer is the same as or thinner than the thickness of the first charge-assisted layer.

12. The quantum dot device of claim 1, wherein... The conductivity of the second charge carriers in the buffer layer is greater than that of the second charge carriers in the first charge-assisted layer, and The conductivity of the second charge carrier in the buffer layer is greater than that of the second charge carrier in the light-emitting layer.

13. The quantum dot device of claim 1, further comprising a second charge-assisted layer between the first electrode and the light-emitting layer, the second charge-assisted layer being configured to enhance the transport of the second charge carriers from the first electrode to the light-emitting layer, wherein the second charge carriers are the dominant charge carriers between the first electrode and the light-emitting layer.

14. The quantum dot device of claim 8, wherein the first electron transport material, the hole extraction material, the second electron transport material, or a combination thereof comprises inorganic nanoparticles.

15. The quantum dot device of claim 1, wherein the first charge-assisted layer and the buffer layer each comprise the same or different n-type inorganic nanoparticles.

16. An electronic device comprising a quantum dot device as claimed in any one of claims 1-15.

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