Patent Description:
Unlike bulk material, intrinsic physical characteristics (e.g., energy bandgaps, melting points, etc.) of nanoparticles may be controlled by changing the nanoparticle sizes. For example, semiconductor nanocrystal particles also known as quantum dots when supplied with photoenergy or electrical energy may emit light in a wavelength corresponding to sizes of the quantum dots. Accordingly, a quantum dot may be used as a light emitter configured to emit light of a predetermined wavelength.

Document <CIT> discloses a quantum dot LED device which comprises a ZnO based nano particle based electron injection layer and electron transport wherein wherein the electron transport layer further comprises monoethanolamine as an organic stabilizer.

Quantum dots used as a light emitter in an electronic device, e.g., a display device, has been the subject of recent research. However, quantum dots are different from a conventional light emitter, and thus a new method of improving performance or lifetime of a quantum dot device is of great interest.

An embodiment is to provide a quantum dot device capable of realizing improved performance.

Another embodiment provides an electronic device including the quantum dot device.

According to an embodiment, a quantum dot device includes a first electrode and a second electrode each having a surface opposite the other, a quantum dot layer between the first electrode and the second electrode, an electron transport layer between the quantum dot layer and the second electrode and including first inorganic nanoparticles and a first organic material, and an electron injection layer between the electron transport layer and the second electrode and including second inorganic nanoparticles and a second organic material, wherein a ratio by weight of an amount of the second organic material to a total amount of the second inorganic nanoparticles and the second organic material in the electron injection layer is less than a ratio by weight of an amount of the first organic material to a total amount of the first inorganic nanoparticles and the first organic material in the electron transport layer.

In an embodiment, the ratio by weight of the amount of the second organic material to the total amount of the second inorganic nanoparticles and the second organic material in the electron injection layer may be about <NUM> times to about <NUM> times of the ratio by weight of the amount of the first organic material to a total amount of the first inorganic nanoparticles and the first organic material in the electron transport layer.

In an embodiment, an amount of the second organic material in the electron injection layer may be less than or equal to about <NUM> weight percent (wt%) based on a total amount of the second inorganic nanoparticles and the second organic material.

In an embodiment, a LUMO energy level of the electron injection layer may be shallower than a work function of the second electrode and deeper than a LUMO energy level of the electron transport layer.

In an embodiment, the first inorganic nanoparticles may be metal oxide nanoparticles represented by Zn<NUM>-xQxO, wherein Q is at least one metal excluding Zn, and <NUM>≤x<<NUM>.

In an embodiment, the at least one metal Q may include Mg, Co, Ni, Ga, Al, Ca, Zr, W, Li, Ti, Ta, Sn, Hf, Si, Ba, or a combination thereof.

The second inorganic nanoparticles may be metal oxide nanoparticles that are dispersible in water, alcohol, or a combination thereof.

In an embodiment, the second inorganic nanoparticles may be metal oxide nanoparticles including at least one of Ti, Ce, Sn, Mg, Zr, W, or Al.

In an embodiment, the first inorganic nanoparticles may be metal oxide nanoparticles represented by Zn<NUM>-xQxO, wherein Q is at least one metal excluding Zn, and <NUM>≤x<<NUM>, and the second inorganic nanoparticles may be different from the first inorganic nanoparticles and may be metal oxide nanoparticles including at least one of Ti, Ce, Sn, Mg, Zr, W, or Al.

In an embodiment, the electron injection layer may have a thickness that is less than a thickness of the electron transport layer.

In an embodiment, a thickness of the electron injection layer may be less than or equal to about <NUM> nanometers (nm).

In an embodiment, the electron injection layer may be in contact with the second electrode.

According to another embodiment, a quantum dot device includes a first electrode and a second electrode each having a surface opposite the other, a quantum dot layer between the first electrode and the second electrode, and an electron injection layer between the second electrode and the quantum dot layer and including inorganic nanoparticles and an organic material, wherein an amount of the organic material in the electron injection layer is less than or equal to about <NUM> wt%, based on a total amount of the inorganic nanoparticles and the organic material.

In an embodiment, the inorganic nanoparticles in the electron injection layer may be metal oxide nanoparticles including at least one of Ti, Ce, Sn, Mg, Zr, W, or Al.

In an embodiment, the quantum dot device may further include an electron transport layer between the quantum dot layer and the electron injection layer, the electron transport layer may include metal oxide nanoparticles represented by Zn<NUM>-xQxO, wherein Q is at least one metal excluding Zn, and <NUM>≤x<<NUM>, and the inorganic nanoparticles in the electron injection layer may be metal oxide nanoparticles including at least one of Ti, Ce, Sn, Mg, Zr, W, or Al.

In an embodiment, the electron transport layer may further include an organic material, and an amount of the organic material in the electron injection layer may be less than an amount of the organic material in the electron transport layer.

In an embodiment, a thickness of the electron injection layer may be less than or equal to about <NUM>.

According to another embodiment, a method of manufacturing a quantum dot device includes forming a first electrode, forming a quantum dot layer on the first electrode, forming an electron transport layer including first inorganic nanoparticles on the quantum dot layer, forming an electron injection layer including second inorganic nanoparticles on the electron transport layer, and forming a second electrode on the electron injection layer. , Here, the forming the electron injection layer includes preparing a first dispersion including the second inorganic nanoparticles and a first amount of an organic material, removing at least a portion of the organic material from the first dispersion to prepare a second dispersion including a second amount of organic material less than the first amount of organic material, and coating the second dispersion on the electron transport layer.

In an embodiment, the method may further include providing a polar dispersion medium such as water, at least one alcohol, or a combination thereof to the second dispersion before the coating of the second dispersion.

In an embodiment, an amount of the organic material (excluding the dispersion medium) in the second dispersion may be less than or equal to about <NUM> wt%, based on a total amount of the second inorganic nanoparticles and the organic material.

According to another embodiment, an electronic device including the quantum dot device is provided.

The characteristics of the quantum dot device may be improved.

Hereinafter, example embodiments of the present disclosure will be described in detail so that a person skilled in the art would understand the same. This disclosure may, however, be embodied in many different forms and is not construed as limited to the example embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, including "at least one," unless the content clearly indicates otherwise.

In the following descriptions, it will be understood that, although the terms "first", "second", etc., may be used to describe various elements, components, regions, layers, and/or sections, these elements, components, regions, layers, and/or sections, should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer, or section. Thus, "a first element," "component," "region," "layer," or "section" discussed below could be termed a second element, component, region, layer, or section without departing from the teachings herein.

For example, "about" can mean within one or more standard deviations, or within ± <NUM> percentages (%) of the stated value.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. Like reference numerals designate like elements throughout the specification.

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 can be directly on the other element or intervening elements may also be present.

Hereinafter, the term "combination" includes a mixture and a laminated structure of two or more.

Hereinafter, the term 'metal' includes a metal and a semimetal.

The term "substituted" refers to the replacement of a hydrogen in a compound, for example, a hydrogen on a ring carbon or an amine hydrogen, with deuterium, -F, -Cl, -Br, -I,- SF<NUM>, a hydroxyl group, a cyano group, a nitro group, an amidino group, a hydrazine group, a hydrazone group, a carboxylic acid group or salt thereof, a sulfonic acid group or salt thereof, a phosphoric acid group or salt thereof, a substituted or unsubstituted C<NUM>-C<NUM> alkyl group, a substituted or unsubstituted C<NUM>-C<NUM> alkenyl group, a substituted or unsubstituted C<NUM>-C<NUM> alkynyl group, a substituted or unsubstituted C<NUM>-C<NUM> alkoxy group, a substituted or unsubstituted C<NUM>-C<NUM> cycloalkyl group, a substituted or unsubstituted C<NUM>-C<NUM> heterocycloalkyl group, a substituted or unsubstituted C<NUM>-C<NUM> cycloalkenyl group, a substituted or unsubstituted C<NUM>-C<NUM> heterocycloalkenyl group, a substituted or unsubstituted C<NUM>-C<NUM> aryl group, a substituted or unsubstituted C<NUM>-C<NUM> aryloxy group, a substituted or unsubstituted C<NUM>-C<NUM> arylthio group, a substituted or unsubstituted C<NUM>-C<NUM> heteroaryl group, a substituted or unsubstituted monovalent non-aromatic condensed polycyclic group, or a substituted or unsubstituted monovalent non-aromatic heterocondensed polycyclic group.

Hereinafter, a work function, a HOMO energy level, or a LUMO energy level is expressed as an absolute value from a vacuum level. In addition, when the work function, HOMO energy level, or LUMO energy level is said to be "deep," "high," or "large," absolute values are large based on "<NUM> electron Volts (eV)" of the vacuum level, while when the work function, HOMO energy level, or LUMO energy level is said to be "shallow," "low," or "small," absolute values are small based on "<NUM> eV" of the vacuum level.

Hereinafter, the HOMO energy level is obtained by measuring a photoelectric work function of thin films with a thickness of about <NUM> to about <NUM> using the AC-<NUM> equipment (Riken Keiki Co. ) and by calculating the emission energy due to the photoelectron effect for the irradiated energy by the following relationship equation in the range of about <NUM> eV to about <NUM> eV. <MAT> (h: planks constant, c: speed of light, and λ: wavelength).

The LUMO energy level may be a value measured by ultraviolet photoelectron spectroscopy (UPS).

The term, 'metal' as used herein may include a metal and a semi-metal.

A quantum dot device according to an embodiment is described with reference to drawings.

<FIG> is a schematic cross-sectional view of a quantum dot device according to an embodiment.

Referring to <FIG>, a quantum dot device <NUM> according to an embodiment includes a first electrode <NUM> and a second electrode <NUM> each having a surface facing the other; a quantum dot layer <NUM> between the first electrode <NUM> and the second electrode <NUM>; a hole transport layer <NUM> and a hole injection layer <NUM> between the first electrode <NUM> and the quantum dot layer <NUM>; and an electron transport layer <NUM> and an electron injection layer <NUM> between the second electrode <NUM> and the quantum dot layer <NUM>.

The substrate (not shown) may be disposed under the first electrode <NUM> or may be disposed on the second electrode <NUM>. The substrate may be, for example, made of an inorganic material such as glass; an organic material such as polycarbonate, polymethylmethacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, polyethersulfone, or a combination thereof; or a silicon wafer. The substrate may be omitted.

One of the first electrode <NUM> and the second electrode <NUM> is an anode and the other is a cathode. For example, the first electrode <NUM> may be an anode and the second electrode <NUM> may be a cathode. For example, the first electrode <NUM> may be a cathode and the second electrode <NUM> may be an anode.

The anode may include a conductor having a high work function, for example, a metal, a conductive metal oxide, or a combination thereof. The anode may include, for example, a metal such as nickel, platinum, vanadium, chromium, copper, zinc, or gold, or an alloy thereof; a conductive metal oxide such as zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or a fluorine-doped tin oxide; or a combination of metal and oxide such as ZnO and Al or SnO<NUM> and Sb, but is not limited thereto.

The cathode may include a conductor having a lower work function than the anode, and may include, for example, a metal, a conductive metal oxide, and/or a conductive polymer. The cathode may include, for example, a metal such as aluminum, magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium silver, tin, lead, cesium, barium, and the like, or an alloy thereof; a multi-layer structure such as LiF/Al, Li<NUM>O/Al, Liq/Al, LiF/Ca, and BaF<NUM>/Ca, but is not limited thereto.

A work function of the anode may be higher than a work function of the cathode, for example the work function of the anode may be, for example, about <NUM> eV to about <NUM> eV and the work function of the cathode may be about <NUM> eV to about <NUM> eV. Within this range, the work function of the anode may be, for example, about <NUM> eV to about <NUM> eV or about <NUM> eV to about <NUM> eV, and the work function of the cathode may be, for example, about <NUM> eV to about <NUM> eV or about <NUM> eV to about <NUM> eV.

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

The quantum dot layer <NUM> includes quantum dots. The quantum dots may be a semiconductor nanocrystal, and may have various shapes, for example a sphere semiconductor nanocrystal, a quantum rod, or a quantum plate. Herein, the quantum rod may be a quantum dot having an aspect ratio (length : width ratio) of greater than about <NUM>, for example, greater than or equal to about <NUM>, greater than or equal to about <NUM>, or greater than or equal to about <NUM>. For example, the quantum rod may have an aspect ratio of less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>.

The quantum dot may have, for example, an average particle diameter (an average largest particle length for a non-spherical shape) of for example about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to <NUM>.

Energy bandgaps of quantum dots may be controlled according to sizes and compositions of the quantum dots, and thus, the light emitting wavelength may be controlled. For example, as the sizes of quantum dots increase, the quantum dots may have narrow energy bandgaps and thus configured to emit light in a relatively long wavelength region while as the sizes of the quantum dots decrease, the quantum dots may have wide energy bandgap and thus configured to emit light in a relatively short wavelength region.

For example, the quantum dot may be configured to emit light in a predetermined wavelength region of a visible ray region according to its size and/or composition. For example, the quantum dot may be configured to emit blue light, red light, or green light, and the blue light may have for example a peak emission wavelength (λmax) in about <NUM> to about <NUM>, the red light may have for example a peak emission wavelength (λmax) in about <NUM> to about <NUM>, and the green light may have for example a peak emission wavelength (λmax) in about <NUM> to about <NUM>.

For example, an average particle size of the quantum dot configured to emit blue light may be, for example, less than or equal to about <NUM>, and for example, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>. Within a range, for example, the average particle size of the quantum dot may be about <NUM> to about <NUM>, for example, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

The quantum dot may have for example a quantum yield of greater than or equal to about <NUM>%, greater than or equal to about <NUM>%, greater than or equal to about <NUM>%, greater than or equal to about <NUM>%, greater than or equal to about <NUM>%, greater than or equal to about <NUM>% or greater than or equal to about <NUM>%.

The quantum dot may have a relatively narrow full width at half maximum (FWHM). Herein, the FWHM is a width of a wavelength corresponding to a half of a peak absorption point and as the FWHM is narrower, light in a narrower wavelength region may be configured to emit and higher color purity may be obtained. The quantum dot may have for example a FWHM of less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>. Within the range, it may have for example FWHM of about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

For example, the quantum dot may include a Group II-VI semiconductor compound, a Group III-V semiconductor compound, a Group IV-VI semiconductor compound, a Group IV semiconductor, a Group I-III-VI semiconductor compound, a Group I-II-IV-VI semiconductor compound, a Group II-III-V semiconductor compound, or a combination thereof. The Group II-VI semiconductor compound may be for example selected from a binary element compound such as CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, MgSe, MgS, or a mixture thereof; a ternary element compound such as CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, MgZnSe, MgZnS, or a mixture thereof; and a quaternary element compound such as HgZnTeS, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, HgZnSTe, or a mixture thereof, but is not limited thereto. The Group III-V semiconductor compound may be for example selected from a binary element compound such as GaN, GaP, GaAs, GaSb, AIN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, or a mixture thereof; a ternary element compound such as GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AINP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, or a mixture thereof; and a quaternary element compound such as GaAlNP, GaAINAs, GaAINSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAINAs, InAINSb, InAlPAs, InAlPSb, or a mixture thereof, but is not limited thereto. The Group IV-VI semiconductor compound may be for example selected from a binary element compound such as SnS, SnSe, SnTe, PbS, PbSe, PbTe, or a mixture thereof; a ternary element compound such as SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, or a mixture thereof; and a quaternary element compound such as SnPbSSe, SnPbSeTe, SnPbSTe, or a mixture thereof, but is not limited thereto. The Group IV semiconductor may be for example selected from a singular element semiconductor such as Si, Ge, or a mixture thereof; and a binary element semiconductor compound such as SiC, SiGe, and a mixture thereof, but is not limited thereto. The Group I-III-VI semiconductor compound may be for example CuInSe<NUM>, CuInS<NUM>, CuInGaSe, CuInGaS, or a mixture thereof, but is not limited thereto. The Group I-II-IV-VI semiconductor compound may be for example CuZnSnSe, CuZnSnS, or a mixture thereof, but is not limited thereto. The Group II-III-V semiconductor compound may include for example InZnP, but is not limited thereto.

The quantum dot may include the singular element semiconductor, the binary semiconductor compound, the ternary semiconductor compound, or the quaternary semiconductor compound in a substantially uniform concentration or partially different concentration distributions.

For example, the quantum dot may include a cadmium (Cd)-free quantum dot. The cadmium-free quantum dot is a quantum dot that does not include cadmium (Cd). Cadmium (Cd) may cause severe environment/health problems and is a restricted element by Restriction of Hazardous Substances Directive (RoHS) in a plurality of countries, and thus the non-cadmium-based quantum dot may be effectively used.

As an example, the quantum dot may be a semiconductor compound including zinc (Zn), and at least one of tellurium (Te) and selenium (Se). For example, the quantum dot may be a Zn-Te semiconductor compound, a Zn-Se semiconductor compound, and/or a Zn-Te-Se semiconductor compound. For example, an amount of tellurium (Te) in the Zn-Te-Se semiconductor compound may be smaller than an amount of selenium (Se). The semiconductor compound may have a peak emission wavelength (λmax) in a wavelength region of less than or equal to about <NUM>, for example, about <NUM> to about <NUM>, and may be configured to emit blue light.

For example, the quantum dot may be a semiconductor compound including indium (In) and at least one of zinc (Zn) and phosphorus (P). For example, the quantum dot may be an In-P semiconductor compound and/or an In-Zn-P semiconductor compound. For example, in the In-Zn-P semiconductor compound, a mole ratio of zinc (Zn) to indium (In) may be greater than or equal to about <NUM>. The semiconductor compound may have a peak emission wavelength (λmax) in a wavelength region of less than about <NUM>, for example about <NUM> to about <NUM>, and may be configured to emit red light.

The quantum dot may have a core-shell structure wherein one quantum dot surrounds another quantum dot. For example, the core and the shell of the quantum dot may have an interface, and an element of at least one of the core or the shell in the interface may have a concentration gradient wherein the concentration of the element(s) of the shell decreases toward the core. For example, a material composition of the shell of the quantum dot has a higher energy bandgap than a material composition of the core of the quantum dot, and thereby the quantum dot may exhibit a quantum confinement effect.

The quantum dot may have one quantum dot core and a multi-layered quantum dot shell surrounding the core. Herein, the multi-layered shell has at least two shells wherein each shell may be a single composition, an alloy, and/or the one having a concentration gradient. For example, a shell of a multi-layered shell that is far from the core may have a higher energy bandgap than a shell that is near to the core, and thereby the quantum dot may exhibit a quantum confinement effect.

The quantum dot having a core-shell structure may for example include a core including a first semiconductor compound including zinc (Zn) and at least one of tellurium (Te) and selenium (Se) and a shell including a second semiconductor compound disposed on at least a portion of the core and having a different composition from that of the core. For example, the first semiconductor compound may be a Zn-Te-Se-based semiconductor compound including zinc (Zn), tellurium (Te), and selenium (Se), for example, a Zn-Se-based semiconductor compound including a small amount of tellurium (Te), for example, a semiconductor compound represented by ZnTexSe<NUM>-x, where x is greater than about <NUM> and less than or equal to <NUM>.

In the Zn-Te-Se-based first semiconductor compound, a mole amount of zinc (Zn) may be higher than that of selenium (Se), and a mole amount of selenium (Se) may be higher than that of tellurium (Te). For example, in the first semiconductor compound, a mole ratio of tellurium (Te) to selenium (Se) may be less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>. For example, in the first semiconductor compound, a mole ratio of tellurium (Te) to zinc (Zn) may be less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>.

The second semiconductor compound may include, for example, a Group II-VI semiconductor compound, a Group III-V semiconductor compound, a Group IV-VI semiconductor compound, a Group IV semiconductor, a Group I-III-VI semiconductor compound, a Group I-II-IV-VI semiconductor compound, a Group II-III-V semiconductor compound, or a combination thereof. Examples of the Group II-VI semiconductor compound, Group III-V semiconductor compound, Group IV-VI semiconductor compound, Group IV semiconductor, Group I-III-VI semiconductor compound, Group I-II-IV-VI semiconductor compound, and Group II-III-V semiconductor compound are the same as described above.

For example, the second semiconductor compound may include zinc (Zn), selenium (Se), and/or sulfur (S). For example, the shell may include ZnSeS, ZnSe, ZnS, or a combination thereof. For example, the shell may include at least one inner shell disposed close to the core and an outermost shell disposed at the outermost side of the quantum dot. The inner shell may include ZnSeS, ZnSe, or a combination thereof and the outermost shell may include ZnS. For example, the shell may have a concentration gradient of one component and for example an amount of sulfur (S) may increase as being apart from the core.

A quantum dot having a core-shell structure may include a core including a third semiconductor compound including indium (In) and at least one of zinc (Zn) and phosphorus (P) and a shell disposed on at least a portion of the core and including a fourth semiconductor compound having a composition different from the core. In the In-Zn-P-based third semiconductor compound, a mole ratio of zinc (Zn) to indium (In) may be greater than or equal to about <NUM>. For example, in the In-Zn-P-based third semiconductor compound, the mole ratio of zinc (Zn) to indium (In) may be greater than or equal to about <NUM>, greater than or equal to about <NUM>, or greater than or equal to about <NUM>. For example, in the In-Zn-P-based third semiconductor compound, the mole ratio of zinc (Zn) to indium (In) may be less than or equal to about <NUM>, for example less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>.

The fourth semiconductor compound may include, for example, a Group II-VI semiconductor compound, a Group III-V semiconductor compound, a Group IV-VI semiconductor compound, a Group IV semiconductor, a Group I-III-VI semiconductor compound, a Group I-II-IV-VI semiconductor compound, a Group II-III-V semiconductor compound, or a combination thereof. Examples of the Group II-VI semiconductor compound, Group III-V semiconductor compound, Group IV-VI semiconductor compound, Group IV semiconductor, Group I-III-VI semiconductor compound, Group I-II-IV-VI semiconductor compound, and Group II-III-V semiconductor compound are the same as described above.

The fourth semiconductor compound may include zinc (Zn) and sulfur (S) and optionally selenium (Se). For example, the shell may include ZnSeS, ZnSe, ZnS, or a combination thereof. The shell may include at least one inner shell disposed close to the core and an outermost shell disposed at the outermost side of the quantum dot. At least one of the inner shell and the outermost shell may include a fourth semiconductor compound of ZnS, ZnSe, or ZnSeS.

The quantum dot layer <NUM> may have a thickness of, for example, about <NUM> to about <NUM>, within the range, for example, about <NUM> to about <NUM>, for example about <NUM> to about <NUM>, for example about <NUM> to about <NUM>.

The quantum dot layer <NUM> may have a relatively deep HOMO energy level, for example, a HOMO energy level of greater than or equal to about <NUM> eV, within the range, for example greater than or equal to about <NUM> eV, for example greater than or equal to about <NUM> eV, for example greater than or equal to about <NUM> eV, for example about greater than or equal to about <NUM> eV, for example greater than or equal to about <NUM> eV, for example greater than or equal to about <NUM> eV. Within the range, the HOMO energy level of the quantum dot layer <NUM> may be for example about <NUM> eV to about <NUM> eV, for example about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM>. 1eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM>. 1eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV.

The quantum dot layer <NUM> may have a relatively shallow LUMO energy level, for example, less than or equal to about <NUM> eV, within the range, for example, less than or equal to about <NUM> eV, for example, less than or equal to about <NUM> eV, for example, less than or equal to about <NUM> eV, for example less than or equal to about <NUM> eV, for example, less than or equal to about <NUM> eV, for example, less than or equal to about <NUM> eV. Within the range, the LUMO energy level of the quantum dot layer <NUM> may be about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV.

The quantum dot layer <NUM> may have an energy band gap of about <NUM> eV to about <NUM> eV or about <NUM> eV to about <NUM> eV. Within the range, for example, the quantum dot layer <NUM> may have an energy band gap of about <NUM> eV to about <NUM> eV or about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV.

The hole transport layer <NUM> and the hole injection layer <NUM> are disposed between the first electrode <NUM> and the quantum dot layer <NUM>. The hole transport layer <NUM> is disposed close to the quantum dot layer <NUM> between the first electrode <NUM> and the quantum dot layer <NUM>, and the hole injection layer <NUM> is disposed close to the first electrode <NUM> between the first electrode <NUM> and the quantum dot layer <NUM>. The hole injection layer <NUM> may facilitate injection of holes from the first electrode <NUM>, and the hole transport layer <NUM> may effectively transfer the injected holes to the quantum dot layer <NUM>. The hole transport layer <NUM> and the hole injection layer <NUM> may have one or two or more layers, respectively, and may include an electron blocking layer in a broad sense.

The hole transport layer <NUM> and the hole injection layer <NUM> may each have a HOMO energy level between the work function of the first electrode <NUM> and the HOMO energy level of the quantum dot layer <NUM>. For example, the work function of the first electrode <NUM>, the HOMO energy level of the hole injection layer <NUM>, the HOMO energy level of the hole transport layer <NUM>, and the HOMO energy level of the quantum dot layer <NUM> may gradually become deeper, and may be, for example, stepped.

The hole transport layer <NUM> may have a relatively deep HOMO energy level so as to match the HOMO energy level of the quantum dot layer <NUM>. Accordingly, mobility of holes transferred from the hole transport layer <NUM> to the quantum dot layer <NUM> may be improved.

The HOMO energy level of the hole transport layer <NUM> may be equal to or smaller than the HOMO energy level of the quantum dot layer <NUM> within a range of about <NUM> eV or less. For example, a difference between the HOMO energy level of the hole transport layer <NUM> and the quantum dot layer <NUM> may be about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, within the range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV.

The HOMO energy level of the hole transport layer <NUM> may be, for example, greater than or equal to about <NUM> eV, within the range, for example, greater than or equal to about <NUM> eV, within the range, for example, greater than or equal to about <NUM> eV, within the range, for example, greater than or equal to about <NUM> eV, within the range, for example, greater than or equal to about <NUM> eV.

For example, the HOMO energy level of the hole transport layer <NUM> may be about <NUM> eV to about <NUM> eV, within the above range, for example, about <NUM> eV to about <NUM> eV, within the above range, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV, for example, about <NUM> eV to about <NUM> eV.

The hole transport layer <NUM> and the hole injection layer <NUM> may include a material satisfying the energy level without particular limitation, and may include for example at least one selected from poly(<NUM>,<NUM>-dioctyl-fluorene-co-N-(<NUM>-butylphenyl)-diphenylamine) (TFB), poly(N,N'-bis-<NUM>-butylphenyl-N,N'-bisphenyl)benzidine (poly TPD), polyarylamine, poly(N-vinylcarbazole), poly(<NUM>,<NUM>-ethylenedioxythiophene) (PEDOT), poly(<NUM>,<NUM>-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), polyaniline, polypyrrole, N,N,N',N'-tetrakis (<NUM>-methoxyphenyl)-benzidine (TPD), <NUM>,<NUM>'-bis[N-(<NUM>-naphthyl)-N-phenyl-amino]biphenyl (α-NPD), m-MTDATA (<NUM>,<NUM>',<NUM>"-tris[phenyl(m-tolyl)amino]triphenylamine), <NUM>,<NUM>',<NUM>"-tris(N-carbazolyl)-triphenylamine (TCTA), <NUM>,<NUM>-bis[(di-<NUM>-tolylamino)phenyl]cyclohexane (TAPC), p-type metal oxide (e.g., NiO, WO<NUM>, MoO<NUM>, etc.), a carbon-based material such as graphene oxide, and a combination thereof, but are not limited thereto.

One or both of the hole transport layer <NUM> and the hole injection layer <NUM> may be omitted.

The electron transport layer <NUM> and the electron injection layer <NUM> are disposed between the second electrode <NUM> and the quantum dot layer <NUM>. The electron transport layer <NUM> is disposed close to the quantum dot layer <NUM> between the second electrode <NUM> and the quantum dot layer <NUM>, and the electron injection layer <NUM> is disposed close to the second electrode <NUM> between the second electrode <NUM> and the quantum dot layer <NUM>. The electron injection layer <NUM> may facilitate injection of electrons from the second electrode <NUM>, and the electron transport layer <NUM> may effectively transfer the injected electrons to the quantum dot layer <NUM>. The electron transport layer <NUM> and the electron injection layer <NUM> may have one or two or more layers, respectively, and may include a hole blocking layer in a broad sense.

For example, the electron injection layer <NUM> may be in contact with the second electrode <NUM>.

For example, the electron transport layer <NUM> may be in contact with the quantum dot layer <NUM>.

For example, the electron transport layer <NUM> and the electron injection layer <NUM> may be in contact with each other.

For example, the LUMO energy levels of the second electrode <NUM>, the electron injection layer <NUM>, the electron transport layer <NUM>, and the quantum dot layer <NUM> may be gradually shallowed. For example, the LUMO energy level of the electron injection layer <NUM> may be shallower than the work function of the second electrode <NUM>, and the LUMO energy level of the electron transport layer <NUM> may be shallower than the LUMO energy level of the electron injection layer <NUM>, and the LUMO energy level of the quantum dot layer <NUM> may be shallower than the LUMO energy level of the electron transport layer <NUM>. That is, the work function of the second electrode <NUM>, the LUMO energy level of the electron injection layer <NUM>, the LUMO energy level of the electron transport layer <NUM>, and the LUMO energy level of the quantum dot layer <NUM> may have a cascading energy level which gradually decreases in one direction.

The electron transport layer <NUM> may include first inorganic nanoparticles. The first inorganic nanoparticles may be, for example, oxide nanoparticles, and may be, for example, metal oxide nanoparticles.

The first inorganic nanoparticles may be two-dimensional or three-dimensional nanoparticles with an average particle diameter of less than or equal to about <NUM>, within the range, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>, or within the range, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

The first inorganic nanoparticles may be a metal oxide nanoparticle including at least one metal 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), or barium (Ba).

As an example, the first inorganic nanoparticles may include metal oxide nanoparticles including zinc (Zn), and may include metal oxide nanoparticles represented by Zn<NUM>-xQxO (<NUM>≤x<<NUM>). Herein, Q is at least one metal other than Zn, for example 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 a combination thereof. For example, Q may include magnesium (Mg).

For example, x may be in the range, <NUM>≦x≦<NUM>, for example, <NUM>≦x≦<NUM>.

For example, the electron transport layer <NUM> may include first inorganic nanoparticles and/or aggregates thereof.

The electron transport layer <NUM> may further include an organic material. The organic material may be a material included in the synthesis step of the first inorganic nanoparticles or may be a material additionally supplied to the dispersion including the first inorganic nanoparticles. For example, the material included in the synthesis step of the first inorganic nanoparticles may be an organic counteranion of a salt included as a precursor of the first inorganic nanoparticles. For example, the organic material additionally supplied to the dispersion including the first inorganic nanoparticles may be a dispersing agent to prevent aggregation of the first inorganic nanoparticles, for example, or an auxiliary agent to control electrical characteristics of the electron transport layer <NUM>.

The organic material may be derived from, for example, acetate; carbonyl; carboxylate; acetyl acetonate; an organic amine, or a combination thereof, but is not limited thereto. Herein, the organic amine may include, for example, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a combination thereof, and may include, for example, trimethylamine, triethylamine, tripropylamine, tributylamine, or a combination thereof, but is not limited thereto.

The organic material in the electron transport layer <NUM> may be disposed on the surface of the first inorganic nanoparticles and/or between adjacent first inorganic nanoparticles to prevent or minimize aggregation of the first inorganic nanoparticles. Accordingly, it is possible to improve dispersibility of the first inorganic nanoparticles by effectively preventing aggregation of the first inorganic nanoparticles in the dispersion for the electron transport layer including the first inorganic nanoparticles.

The organic material in the electron transport layer <NUM> may be in an amount of greater than or equal to about <NUM> weight percent (wt%), for example greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, greater than or equal to about <NUM> wt%, or greater than or equal to about <NUM> wt%, based on a total amount of the first inorganic nanoparticles and the organic material (excluding a dispersion medium) in the electron transport layer <NUM>. Within the range, the organic material in the electron transport layer <NUM> may be in an amount of about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt% or about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%.

By including the organic material within the above ranges in the electron transport layer <NUM>, aggregation of the first inorganic nanoparticles may be minimized, or effectively prevented from aggregation, in the first inorganic nanoparticle dispersion including the first inorganic nanoparticles, thereby effectively improving dispersibility of the first inorganic nanoparticles and ultimately improving coatability, morphology, and electrical properties of the electron transport layer <NUM>.

The LUMO energy level of the electron transport layer <NUM> may be a value between the LUMO energy level of the quantum dot layer <NUM> and the LUMO energy level of the electron injection layer <NUM> to be described later, and may be about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV.

A thickness of the electron transport layer <NUM> may be greater than about <NUM> and less than or equal to about <NUM>, and within the range, greater than about <NUM> and less than or equal to about <NUM>, greater than about <NUM> and less than or equal to about <NUM>, greater than about <NUM> and less than or equal to about <NUM>, greater than about <NUM> and less than or equal to about <NUM>, or greater than about <NUM> and less than or equal to about <NUM>.

The electron injection layer <NUM> may include second inorganic nanoparticles different from the first inorganic nanoparticles. The second inorganic nanoparticles may be, for example, oxide nanoparticles, and may be, for example, metal oxide nanoparticles. The second inorganic nanoparticle may be selected in consideration of a relationship between the LUMO energy level of the electron transport layer <NUM> and the electron injection layer <NUM>. The second inorganic nanoparticles may be selected so that the LUMO energy level of the electron injection layer <NUM> including the second inorganic nanoparticles is deeper than the LUMO energy level of the electron transport layer <NUM> including the aforementioned first inorganic nanoparticles.

The second inorganic nanoparticles may be two-dimensional or three-dimensional nanoparticles with an average particle diameter of less than or equal to about <NUM>, within the range, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>, or within the range, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

For example, the second inorganic nanoparticles may be hydrophilic metal oxide nanoparticles dispersible in a polar dispersion medium, wherein the polar dispersion medium may be for example water; alcohols such as methanol, ethanol, propanol, and butanol; or a combination thereof. The second inorganic nanoparticles may have a higher dispersibility in the dispersion medium than the first inorganic nanoparticles, and such high dispersibility may be caused by interactions such as binding energy, van der Waals energy, and repulsion forces between the second inorganic nanoparticles, but the present disclosure is not limited thereto.

The second inorganic nanoparticles may be selected from materials having a higher dispersibility in the dispersion medium than the first inorganic nanoparticles and may be, for example, metal oxide nanoparticle including at least one metal of titanium (Ti), cerium (Ce), tin (Sn), magnesium (Mg), zirconium (Zr), tungsten (W), or aluminum (Al). The second inorganic nanoparticles may be for example TiO<NUM>, CeO<NUM>, SnO<NUM>, MgO, ZrO<NUM>, WO<NUM>, Al<NUM>O<NUM>, or a combination thereof, but are not limited thereto.

The electron injection layer <NUM> may further include an organic material. The organic material in the electron injection layer <NUM> may be the same as or different from the organic material in the electron transport layer <NUM>. The organic material may be, for example, a material included in the synthesis step of the second inorganic nanoparticles, and may be derived from an organic counteranion of a salt included as a precursor of the second inorganic nanoparticle, such as acetate, carbonyl, carboxylate, acetyl acetonate, organic amine (or organic amine salt), or a combination thereof, but is not limited thereto. Herein, the organic amine may include, for example, a substituted or unsubstituted C1 to C10 alkyl group, a substituted or unsubstituted C6 to C20 aryl group, or a combination thereof, and may include, for example, trimethylamine, triethylamine, tripropylamine, tributylamine, or a combination thereof, but is not limited thereto.

The organic material in the electron injection layer <NUM> may be controlled to a predetermined amount. While the organic material in the electron injection layer <NUM> may exhibit an effect of preventing or minimizing aggregation of the second inorganic nanoparticles on the surface of the second inorganic nanoparticles and/or between adjacent second inorganic nanoparticles, an excessive amount of organic material in the electron injection layer <NUM> may interfere with the injection of electrons from the second electrode <NUM>, thereby increasing a driving voltage of the quantum dot device <NUM> and reducing the life-span of the quantum dot device <NUM>.

For example, in the step of preparing a dispersion of the second inorganic nanoparticles including the second inorganic nanoparticles, the amount of the organic material may be reduced by removing at least a portion of the organic material. The removing of the organic material may include, for example, centrifugation, precipitation using a solvent and/or dispersion medium, redistribution, and/or washing, but is not limited thereto. In this manner, the electron injection layer <NUM> may include less organic material than the electron transport layer <NUM> by including an organic material having a controlled amount. In the claimed invention, a ratio by weight of an amount of the organic material to a total amount of the second inorganic nanoparticles and the organic material in the electron injection layer <NUM> may be less than a ratio by weight of an amount of the organic material to a total amount of the first inorganic nanoparticles and the organic material in the electron transport layer <NUM>. For example, the ratio by weight of the amount of the organic material to a total amount of the second inorganic nanoparticles and the second organic material in the electron injection layer <NUM> may be about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, or about <NUM> times to about <NUM> times of the ratio by weight of the amount of the organic material to a total amount of the first inorganic nanoparticles and the first organic material in the electron transport layer <NUM>, but is not limited thereto.

As described above, the second inorganic nanoparticles in the electron injection layer <NUM> may have a higher dispersibility in the dispersion medium than the first inorganic nanoparticles in the electron transport layer <NUM>, and thus even when the organic material in the electron injection layer <NUM> has a controlled amount, excessive aggregation of the second inorganic nanoparticles may be minimized or, at times, prevented. In addition, as will be described later, since the electron injection layer <NUM> has a thickness of less than or equal to about <NUM>, even if the electron injection layer has a controlled amount of the organic material, the effect on coatability, morphology, and electrical characteristics of the electron injection layer <NUM> may become negligible.

The amount of the organic material in the electron injection layer <NUM> may be controlled to a range capable of preventing or minimizing aggregation of the second inorganic nanoparticles and at the same time effectively improving the injection of electrons from the second electrode <NUM>. For example, the amount of the organic material in the electron injection layer <NUM> may be controlled to be less than or equal to about <NUM> wt% based on a total amount of the second inorganic nanoparticles and the organic material. Within the range, the amount of the organic material in the electron injection layer <NUM> may be controlled to be less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, or less than or equal to about <NUM> wt% based on a total amount of the second inorganic nanoparticles and the organic material. Within the range, it may be controlled to be about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%.

A LUMO energy level of the electron injection layer <NUM> may be between the work function of the second electrode <NUM> and the LUMO energy level of the electron transport layer <NUM>. For example, a difference between the work function of the second electrode <NUM> and the LUMO energy level of the electron injection layer <NUM> may be less than about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV. As an example, a difference between the LUMO energy level of the electron injection layer <NUM> and the LUMO energy level of the electron transport layer <NUM> may be less than about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV. Accordingly, electrons from the second electrode <NUM> into the electron injection layer <NUM> may be easily injected to lower a driving voltage of the quantum dot device <NUM>, and electrons from the electron injection layer <NUM> to the electron transport layer <NUM> may be effectively transferred to increase efficiency. The LUMO energy level of the electron injection layer <NUM> may be, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV within the range satisfying the aforementioned energy level.

The electron injection layer <NUM> may have a thickness that is less than the thickness of the electron transport layer <NUM>. For example, a thickness of the electron injection layer <NUM> may be about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, or about <NUM> times to about <NUM> times of the thickness of the electron transport layer <NUM>. The thickness of the electron injection layer <NUM> may be, for example, less than or equal to about <NUM>, less than or equal to about <NUM>, or less than or equal to about <NUM>. Within the range, the thickness of the electron injection layer <NUM> may be about <NUM> to about <NUM>, about <NUM> to about <NUM>, about <NUM> to about <NUM>, or about <NUM> to about <NUM>.

The quantum dot device <NUM> includes an electron injection layer <NUM> including an organic material of a controlled amount between the second electrode <NUM> and the electron transport layer <NUM>, and thereby the electron injection may be effectively facilitated, and the injected electrons may be effectively transferred to the quantum dot layer <NUM> through the electron transport layer <NUM>. Therefore, it is possible to effectively lower a driving voltage of the quantum dot device <NUM>, thereby improving luminance and life-span.

For example, the driving voltage (@<NUM> mA) of the quantum dot device <NUM> may be less than or equal to about <NUM> Volts (V), and within the range, less than or equal to about <NUM> V, less than or equal to about <NUM> eV, less than or equal to about <NUM> eV, less than or equal to about <NUM> eV, or less than or equal to about <NUM> eV. As an example, the driving voltage (@<NUM> mA) of the quantum dot device <NUM> may be lower than that of the quantum dot device that does not include the aforementioned electron injection layer <NUM>, by about <NUM> eV to about <NUM> eV, within the above range, about <NUM> eV to about <NUM> eV, or about <NUM> eV to about <NUM> eV.

The luminance characteristics of the quantum dot device <NUM> may be improved compared with the quantum dot device that does not include the aforementioned electron injection layer <NUM>, by about <NUM> times to about <NUM> times, and within the range, about <NUM> times to about <NUM> times, or about <NUM> times to about <NUM> times. As an example, the life-span characteristics (T95 or T80) of the quantum dot device <NUM> may be improved compared with the quantum dot device that does not include the aforementioned electron injection layer <NUM>, by about <NUM> times to about <NUM> times, and within the range, about <NUM> times to about <NUM> times, or about <NUM> times to about <NUM> times.

For example, a method of manufacturing a quantum dot device <NUM> may include forming a first electrode <NUM> on a substrate (not shown), forming a hole injection layer <NUM>, forming a hole transport layer <NUM>, forming a quantum dot layer <NUM>, forming an electron transport layer <NUM>, forming an electron injection layer <NUM>, and forming a second electrode <NUM>. One or both of the forming of the hole injection layer <NUM> or the forming of the hole transport layer <NUM> may be omitted.

The quantum dot layer <NUM>, the hole transport layer <NUM>, the hole injection layer <NUM>, the electron transport layer <NUM>, and/or the electron injection layer <NUM> may be formed by a solution process, such as spin coating, slit coating, inkjet printing, nozzle printing, spraying, and/or doctor blade coating, but is not limited thereto.

In at least some of the aforementioned steps the method of manufacturing a quantum dot device <NUM>, the forming of the quantum dot layer <NUM>, the forming of the hole transport layer <NUM>, the forming of the hole injection layer <NUM>, the forming of the electron transport layer <NUM>, and/or the forming of the electron injection layer <NUM>, may optionally include drying after the solution process and/or heat-treating may be further performed, and the heat-treating may be, for example, performed at about <NUM> to about <NUM> for about <NUM> minute to about <NUM> hours, but is not limited thereto.

For example, the forming of the electron transport layer <NUM> may include coating first inorganic nanoparticle dispersion including the first inorganic nanoparticles, and optionally drying and/or heat-treating. The first inorganic nanoparticles may be obtained by a sol-gel synthesis method using a metal salt, but is not limited thereto. The dispersion medium may be water; alcohols such as methanol, ethanol, propanol, or butanol; or a combination thereof, but is not limited thereto. The forming the electron transport layer <NUM> may include centrifugation and/or washing.

For example, the forming of the electron injection layer <NUM> may include coating second inorganic nanoparticle dispersion including second inorganic nanoparticles, and optionally drying and/or heat-treating. The second inorganic nanoparticles may be obtained by a sol-gel synthesis method using a metal salt, but is not limited thereto. The dispersion medium may be water; alcohols such as methanol, ethanol, propanol, or butanol; or a combination thereof, but is not limited thereto.

The forming of the electron injection layer <NUM> may further include removing at least some of the excess organic material from the dispersion in order to control the amount of the organic material as described above. For example, the forming of the electron injection layer <NUM> may include preparing a first dispersion including second inorganic nanoparticles and a first amount of organic material, that is, having an excess amount of organic material, followed by removing at least a portion of the organic material from the first dispersion to prepare a second dispersion including an organic material having a second amount of organic material that is less than the first amount, and coating the second dispersion on the electron transport layer <NUM>.

The removing of at least a portion of the organic material from the first dispersion may include further performing centrifugation one or more times (e.g., <NUM> to <NUM> times, <NUM> to <NUM> times, or <NUM> to <NUM> times), or further performing precipitation, redispersion, and/or washing one or more times (e.g., <NUM> to <NUM> times, <NUM> to <NUM> times, or <NUM> to <NUM> times) using a polar dispersion medium such as water; alcohols such as methanol, ethanol, propanol, and butanol; a combination of at least one alcohol and water, or a combination of at least one alcohol, and/or a non-polar dispersion medium such as hexane, cyclohexane, benzene, toluene, chloroform, diethyl ether, acetone, etc., or a combination thereof, but is not limited thereto.

The amount (second amount) of the organic material in the second dispersion may be less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, or less than or equal to about <NUM> wt%, within the range, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt% of the amount (first amount) of the organic material in the first dispersion.

For example, as described above, the amount (the second amount) of organic material in the second dispersion may be controlled to be less than or equal to about <NUM> wt% based on a total amount of the second inorganic nanoparticles and the organic material (excluding the dispersion medium). Within the range, the amount (the second amount) of organic material may be controlled to be less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about 6wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, less than or equal to about <NUM> wt%, or less than or equal to about <NUM> wt%, within the range; about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, about <NUM> wt% to about <NUM> wt%, or about <NUM> wt% to about <NUM> wt%.

For example, the method may further include diluting the second dispersion before the coating of the second dispersion. The diluting of the second dispersion may further include, for example, further supplying a polar dispersion medium selected from water, at least one alcohol, or a combination thereof to the second dispersion. For example, the step of dilution with the polar dispersion medium may including the addition of about <NUM> times to about <NUM> times, about <NUM> times to about <NUM> times, or about <NUM> times to about <NUM> times of the total volume of the second dispersion.

The aforementioned quantum dot device may be applied to various electronic devices requiring light emission, and may be applied to various electronic devices, for example, a display device such as a TV, a monitor, a computer, and a mobile device, or a lighting device such as a light source.

However, the following examples are for illustrative purposes and do not limit the scope of the rights.

Selenium (Se) and tellurium (Te) are respectively dispersed in trioctylphosphine (TOP) to obtain a <NUM> Molar (M) Se/TOP stock solution and a <NUM> Te/TOP stock solution.

<NUM> millimoles (mmol) of zinc acetate is combined with <NUM> mmol of oleic acid, <NUM> mmol of hexadecylamine, and <NUM> milliliters (mL) of trioctylamine in a reactor, and then heated under vacuum at <NUM>. After <NUM> hour, nitrogen gas is added to the reactor.

Under nitrogen atmosphere, the reactor is heated at <NUM>, and the Se/TOP stock solution and the Te/TOP stock solution in a Te/Se mole ratio of <NUM>/<NUM> are rapidly injected into the reactor. The reaction solution is heated to <NUM>, maintained for <NUM> minutes, and then, rapidly cooled down to room temperature. Acetone is added to the cooled reactor, and the resulting precipitate is separated by centrifugation, and then dispersed in toluene to obtain ZnTeSe core quantum dot dispersion in toluene.

To a <NUM> reaction flask containing trioctylamine <NUM> mmol of zinc acetate and <NUM> mmol of oleic acid are added, and the reaction flask is heated at <NUM> under vacuum for <NUM> minutes. Nitrogen gas is added to the reaction flask. The ZnTeSe core quantum dot dispersion in toluene is rapidly injected into the reaction flask. The <NUM> Se/TOP and the <NUM> S/TOP in a Se:S mole ratio of <NUM>:<NUM> are injected into the reaction flask, and the flask is heated to <NUM>. When the reaction is complete, the reactor is cooled down to ambient temperature and ethanol is added to the flask, and the resulting nanocrystals are separated by centrifugation and dispersed in toluene to obtain ZnTeSe core/ZnSeS shell quantum dot dispersion in toluene.

In a <NUM> reaction flask including <NUM>-octadecene, indium acetate and palmitic acid are added, and the flask is heated at <NUM> under vacuum. The indium and palmitic acid are added as a mole ratio of <NUM>:<NUM>. After <NUM> hour, nitrogen gas is added to the reaction flask, and the flask is heated to <NUM>. A mixed solution of tris(trimethylsilyl)phosphine (TMS<NUM>P) and trioctylphosphine is rapidly injected into the reaction flask, and the reaction mixture is maintained at <NUM> for <NUM> minutes. The TMS<NUM>P is used in an amount of <NUM> mols of TMS<NUM>P per <NUM> mole of indium. The reaction flask is cooled to room temperature and acetone is added to the flask, and the resulting precipitate is separated by centrifugation and dispersed in toluene to prepare InP core quantum dot dispersion in toluene. The InP core quantum dot has an average particle diameter of about <NUM> nanometers (nm).

Selenium (Se) is dispersed in trioctylphosphine (TOP) to prepare a Se/TOP stock solution, and sulfur (S) is dispersed in trioctylphosphine (TOP) to prepare a S/TOP stock solution.

To a <NUM> reaction flask including trioctylamine, zinc acetate and oleic acid are added, and the reaction flask is heated at <NUM> under vacuum for <NUM> minutes. Nitrogen gas is added to the reaction flask, the flask is heated to <NUM>, and the InP core quantum dot dispersion is added to the reaction flask.

The reaction flask is heated to <NUM>, a portion of the Se/TOP is injected into the flask, and the mixture is allowed to react at <NUM>. The reaction flask is then heated to <NUM>, the remainder of Se/TOP is injected into the flask, and the reaction mixture allowed to react for predetermined time to form a ZnSe shell on the InP core. Subsequently, the S/TOP stock solution is added to the reaction mixture, and the mixture is allowed to react for predetermined time to form a ZnS shell on the ZnSe shell to obtain an InP core/ZnSe shell/ZnS shell quantum dot. The ZnSe shell is formed for total reaction time of <NUM> minutes, and a total amount of Se is about <NUM> moles based on <NUM> mole of indium, and the ZnS shell is also formed for total reaction time of <NUM> minutes, and a total amount of S is about <NUM> moles based on <NUM> mole of indium.

The obtained InP core/ZnSe shell/ZnS shell quantum dot is added to an excessive amount of ethanol, and then resulting quantum dot is separated by centrifugation. Following separation, the quantum dot is dried and dispersed in chloroform or toluene to obtain InP core/ZnSe shell/ZnS shell quantum dot dispersion.

<NUM> mmol of zinc acetate dihydrate, <NUM> mmol of magnesium acetate tetrahydrate, and <NUM> of dimethylsulfoxide are added to a reactor, and the reactor is heated at <NUM> under air atmosphere. Subsequently, <NUM> mmol of tetramethylammonium hydroxide pentahydrate is dissolved in <NUM> of ethanol, and then <NUM> of the solution is added to the reactor in a dropwise fashion. After stirring the mixture for <NUM> hour, the obtained Zn<NUM>Mg<NUM>O nanoparticles and the ethyl acetate formed in-situ (in a volume ratio of about <NUM>:<NUM>) are separated by centrifugation and dispersed in ethanol to obtain a Zn<NUM>Mg<NUM>O nanoparticle dispersion.

The Zn<NUM>Mg<NUM>O nanoparticles have an average particle diameter of about <NUM>. The average particle diameter of the Zn<NUM>Mg<NUM>O nanoparticles is measured by using an UT F30 Tecnai electron microscope.

If the Zn<NUM>Mg<NUM>O nanoparticle (ethyl acetate) dispersion is additionally washed with ethanol and redispersed to further reduce an amount of an organic material, i.e., the ethyl acetate, the Zn<NUM>Mg<NUM>O nanoparticles become severely aggregated, and exhibit severe deteriorating dispersibility.

Titanium oxide (TiO<NUM>) nanoparticles (anatase, PlasmaChem) are dispersed in water at a concentration of <NUM> weight percent (wt%) to prepare a titanium oxide nanoparticle dispersion (first dispersion).

The titanium oxide nanoparticle dispersion (first dispersion) is centrifuged, and the separated nanoparticles washed repeatedly, at least twice (e.g., <NUM> to <NUM> times) with butanol, acetone, and hexane, and redispersed to remove an excessive amount of the organic material and obtain a final precipitate. The final precipitate is dispersed in ethanol to obtain titanium oxide nanoparticle dispersion at a concentration of <NUM> wt% (second dispersion). The amount of the organic material in a nanoparticle dispersion may be evaluated by measuring a reduction in the weight of a device, after heating a device to <NUM> at a rate of <NUM>/min with a thermogravimetric analyzer (Q5000, TA Instruments) in a thermal gravimetric analysis (TGA) method.

In the titanium oxide nanoparticle dispersion (second dispersion), a distribution of particle diameters of the titanium oxide nanoparticles are within about <NUM> or less. The particle diameter of the titanium oxide nanoparticles is measured by using a UT F30 Tecnai electron microscope.

Additional ethanol is added to the second dispersion (about three times by volume of to a volume of the titanium oxide nanoparticle dispersion (second dispersion) to obtain a final titanium oxide nanoparticle dispersion at a concentration of <NUM> wt%.

Titanium oxide nanoparticle dispersion is obtained according to the same method as Synthesis Example <NUM> except that an excessive amount of an organic material is not removed from the titanium oxide nanoparticle dispersion (first dispersion).

The tin oxide SnO<NUM> nanoparticles (PlasmaChem) are dispersed in water at a concentration of <NUM> wt% to prepare tin oxide nanoparticle dispersion (first dispersion). Subsequently, the tin oxide nanoparticle dispersion (first dispersion) is centrifuged and the separated particles are repeatedly washed with butanol, acetone, and hexane at least twice (<NUM> to <NUM> times), and redispersed to remove an excessive amount of an organic material and obtain final precipitate. The final precipitate is dispersed in ethanol to obtain tin oxide nanoparticle dispersion at a concentration of <NUM> wt% (second dispersion). In the tin oxide nanoparticle dispersion (second dispersion), a distribution of particle diameters of tin oxide nanoparticles are within about <NUM> or less. A particle diameter distribution of the tin oxide nanoparticles is measured by using a UT F30 Tecnai electron microscope. Additional ethanol is added to the second dispersion (about three times by volume of the tin oxide nanoparticle dispersion (second dispersion) to obtain tin oxide nanoparticle dispersion at a concentration of <NUM> wt%.

Tin oxide nanoparticle dispersion is obtained according to the same method as Synthesis Example <NUM> except that an excessive amount of an organic material is not removed from the tin oxide nanoparticle dispersion (first dispersion).

To evaluate thin film characteristics and simple electrical characteristics, an electron-only device (EOD) is manufactured.

The Zn<NUM>Mg<NUM>O nanoparticle dispersion according to Synthesis Example <NUM> is spin-coated on a glass substrate deposited with ITO (an anode), and heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick electron transport layer. Subsequently, a titanium oxide (TiO<NUM>) nanoparticle dispersion prepared by purifying an organic material according to Synthesis Example <NUM> is spin-coated on the electron transport layer, and heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick electron injection layer. Then, aluminum (Al, a cathode) is vacuum-deposited on the electron injection layer to be <NUM> thick, to provide an electron-only device.

An electron-only device is manufactured according to the same method as Example A except that the electron injection layer is not formed on the electron transport layer.

An electron-only device is manufactured according to the same method as Example A except that the titanium oxide nanoparticle dispersion prepared according to Comparative Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

An electron-only device is manufactured according to the same method as Example A except that the tin oxide SnO<NUM> nanoparticle dispersion according to Synthesis Example <NUM> is used instead of the titanium oxide TiO<NUM> nanoparticle dispersion according to Synthesis Example <NUM>.

An electron-only device is manufactured according to the same method as Example B except that the electron injection layer is not formed on the electron transport layer.

An electron-only device is manufactured according to the same method as Example B except that the SnO<NUM> nanoparticle dispersion according to Comparative Synthesis Example <NUM> instead of the SnO<NUM> dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

In the electron-only devices according to Examples, the surface morphology of the electron injection layers is examined. The surface morphology is evaluated by using a transmission electron microscope (TEM).

<FIG> is a transmission electron microscopic (TEM) photograph of an electron injection layer in the electron-only device according to Example A. Referring to <FIG>, the electron injection layer from the titanium oxide TiO<NUM> nanoparticle dispersion obtained by purifying an organic material according to Synthesis Example <NUM> appears as a uniform thin film with little, if any, aggregation of the titanium oxide nanoparticles.

In the electron-only devices according to Examples and Comparative Examples, an amount of an organic material in the electron transport layers and the electron injection layers is examined. The amount of the organic material is evaluated by measuring a reduced weight, after heat the respective devices to <NUM> at a rate of <NUM>/min with a thermogravimetric analyzer (Q5000, TA Instruments) in a thermal gravimetric analysis (TGA) method. The results are shown in Table <NUM>.

In the electron-only devices according to Examples and Comparative Examples, the amount of carbon in the electron transport layers and the electron injection layers in each of the respective devices are evaluated through an X-ray diffraction (XRD) analysis. The results are shown in Table <NUM>.

Referring to Table <NUM>, the electron-only device according to Example A The XRD data indicates that the amount of the organic material (in terms of amount of carbon present) in the electron transport layer and the electron injection layer is reduced compared to the amount of the organic material in the electron transport layer in the electron-only device according to Comparative Example A-<NUM>.

Current characteristics of the electron-only devices according to Examples and Comparative Examples are evaluated. The current characteristics of the electron-only devices are evaluated by using a Keithley SMU2635B current source. The results are shown in <FIG>.

<FIG> is a graph showing current characteristics of the electron-only devices according to Example A and Comparative Example A-<NUM>. Referring to <FIG>, the electron-only device according to Example A exhibits significantly improved current characteristics, compared to the electron-only device including no electron injection layer according to Comparative Example A-<NUM>.

A glass substrate deposited with ITO (a work function: <NUM> eV) is surface-treated with UV-ozone for <NUM> minutes. A PEDOT:PSS solution (H. Starks) is spin-coated on the ITO, and then heat-treated under an air atmosphere at <NUM> for <NUM> minutes, and heat-treated again under a N<NUM> atmosphere at <NUM> for <NUM> minutes to form a <NUM>-thick lower hole transport layer (HOMO: <NUM> eV, LUMO: <NUM> eV). Subsequently, a poly[(<NUM>,<NUM>-dioctylfluoren-<NUM>,<NUM>-diyl-co-(<NUM>,<NUM>'-(N-<NUM>-butylphenyl)diphenylamine] solution (TFB, Sumitomo Corp. ) is spin-coated on the lower hole transport layer and then heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick upper hole transport layer (HOMO: <NUM> eV, LUMO: <NUM> eV). The ZnTeSe/ZnSeS core shell quantum dot dispersion (a peak emission wavelength: <NUM> to <NUM>) according to Synthesis Example <NUM> is spin-coated on the upper hole transport layer and then heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick quantum dot layer (HOMO: <NUM> eV, LUMO: <NUM> eV). The Zn<NUM>Mg<NUM>O nanoparticle dispersion according to Synthesis Example <NUM> is spin-coated on the quantum dot layer and then heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick electron transport layer (HOMO: <NUM> eV, LUMO: <NUM> eV). The titanium oxide nanoparticle dispersion according to Synthesis Example <NUM> is spin-coated on the electron transport layer and then, heat-treated at <NUM> for <NUM> minutes to form a <NUM>-thick electron injection layer (HOMO: <NUM> eV, LUMO: <NUM> eV). Subsequently, aluminum (Al) is vacuum-deposited on the electron injection layer to form a <NUM>-thick Al electrode (a work function: <NUM> eV), manufacturing a quantum dot device.

A quantum dot device is manufactured according to the same method as Example <NUM>-<NUM> except that a <NUM>-thick electron injection layer is formed.

A quantum dot device is manufactured according to the same method as Example <NUM>-<NUM> except that the electron injection layer is not formed on the electron transport layer.

A quantum dot device is manufactured according to the same method as Example <NUM>-<NUM> except that the titanium oxide nanoparticle dispersion according to Comparative Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion according to Synthesis Example <NUM> is used to form the electron injection layer.

A quantum dot device is manufactured according to the same method as Example <NUM>-<NUM> except that the titanium oxide nanoparticle dispersion according to Synthesis Example <NUM> instead of the Zn<NUM>Mg<NUM>O nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron transport layer, and the Zn<NUM>Mg<NUM>O nanoparticle dispersion according to Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

A quantum dot device is manufactured according to the same method as Example <NUM>-<NUM> except that the InP core/ZnSe shell/ZnS shell quantum dot dispersion (a peak emission wavelength: <NUM> to <NUM>) according to Synthesis Example <NUM> instead of the ZnTeSe/ZnSeS core shell quantum dot dispersion according to Synthesis Example <NUM> is used to form a quantum dot layer (HOMO: <NUM> eV, LUMO: <NUM> eV).

A quantum dot device is manufactured according to the same method as Example <NUM> except that the electron injection layer is not formed on the electron transport layer.

A quantum dot device is manufactured according to the same method as Example <NUM> except that the titanium oxide nanoparticle dispersion according to Comparative Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

A quantum dot device is manufactured according to the same method as Example <NUM> except that the titanium oxide nanoparticle dispersion according to Synthesis Example <NUM> instead of the Zn<NUM>Mg<NUM>O nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron transport layer, and the Zn<NUM>Mg<NUM>O nanoparticle dispersion according to Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

A quantum dot device is manufactured according to the same method as Example <NUM> except that a poly(N,N'-bis-<NUM>-butylphenyl-N,N'-bisphenyl)benzidine instead of TFB is used to form the upper hole transport layer and the tin oxide nanoparticle dispersion according to Synthesis Example <NUM> instead of the titanium oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer (HOMO: <NUM> eV, LUMO: <NUM> eV).

A quantum dot device is manufactured according to the same method as Example <NUM> except that the tin oxide nanoparticle dispersion according to Comparative Synthesis Example <NUM> instead of the tin oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

A quantum dot device is manufactured according to the same method as Example <NUM> except that the tin oxide nanoparticle dispersion according to Synthesis Example <NUM> instead of the Zn<NUM>Mg<NUM>O nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron transport layer, and the Zn<NUM>Mg<NUM>O nanoparticle dispersion according to Synthesis Example <NUM> instead of the tin oxide nanoparticle dispersion of Synthesis Example <NUM> is used to form the electron injection layer.

Current-voltage-luminescence characteristics of the quantum dot devices according to Examples and Comparative examples are evaluated. The current-voltage-luminescence characteristics are evaluated by using a Keithley SMU2635B current source and a Minolta CS-2000A spectroradiometer. Driving voltages thereof are evaluated by using a voltage (a turn-on voltage) for <NUM> mA current driving.

Life-span characteristics thereof are evaluated by using a reduction in luminance from initial luminance as current meeting a condition that a quantum dot device shows luminance of <NUM> nit (blue quantum dot device), or <NUM> nit (red quantum dot device), is applied to the device, and T<NUM> is time it takes to reach <NUM>% of luminance relative to the initial luminance. The results are shown in Tables <NUM> to <NUM>.

Referring to Tables <NUM> to <NUM>, the quantum dot devices according to Examples <NUM>, <NUM> and <NUM>, simultaneously exhibit a low driving voltage, improved luminescence characteristics, and high life-span characteristics, compared with the quantum dot devices according to the Comparative Examples.

Claim 1:
A quantum dot device (<NUM>), comprising:
a first electrode (<NUM>) and a second electrode (<NUM>) each having a surface opposite the other; and
a quantum dot layer (<NUM>) between the first electrode and the second electrode,
and further comprising:
an electron transport layer (<NUM>) between the quantum dot layer and the second electrode, the electron transport layer comprising first inorganic nanoparticles and a first organic material; and
an electron injection layer (<NUM>) between the electron transport layer and the second electrode, characterized in that the electron injection layer comprising second inorganic nanoparticles and a second organic material,
wherein a ratio by weight of an amount of the second organic material to a total amount of the second inorganic nanoparticles and the second organic material in the electron injection layer is less than a ratio by weight of an amount of the first organic material to a total amount of the first inorganic nanoparticles and the first organic material in the electron transport layer.