QUANTUM POINT LED AND QUANTUM POINT LIGHT-EMPLOYING DEVICE WITH THE SAME

Abstract

Light-emitting diode (100, 200) with several quantum dots (10), having the light-emitting diode (100, 200): a first electrode (110, 210) and a second electrode (120, 220); an emitting material layer (150, 250); an electron transfer layer (164, 244); and a hole transfer layer (144, 264), wherein the emitting material layer (150, 250) is arranged between the electron transfer layer (164, 244) and the hole transfer layer (144, 264) and the emitting material layer (150, 250) has the quantum dots (10), where the quantum dots exhibit (10): a semiconductor nanocrystal or metal oxide core (20); a shell (30) covering the semiconductor nanocrystal or metal oxide core (20), wherein the shell (30) has an outer surface; an X-type ligand (42) having a functional group selected from the group consisting of a carboxylate group, a phosphate group and a thiolate group, which is bonded to a first region of the outer surface; and an L-type ligand (44) having a functional group selected from the group consisting of an amino group, a thiol group, a phosphine group and a phosphine oxide group, which is bonded to a second region of the outer surface, wherein the X-type ligand (42) is bound to the first region of the outer surface by a negatively charged functional group, and the L-type ligand (44) is bound to the second region of the outer surface by an undivided electron pair, wherein a multitude of the first regions of the outer surfaces of the quantum dots (10) are proximal to the hole transfer layer (144, 264) and distal to the electron transfer layer (164, 244), wherein a multitude of the second regions of the outer surfaces of the quantum dots (10) are proximal to the electron transfer layer (164, 244) and distal to the hole transfer layer (144, 264), and where the outer surface is spherical and the first area is a first hemisphere and the second area is a second hemisphere.

Description

BACKGROUND Technical area

[0001] The present disclosure relates to a light-emitting diode and in particular to a light-emitting diode which uses quantum dots with different surface properties, and to a light-emitting device which incorporates these. Description of the related technology

[0002] With advances in electrical engineering and information technology, display technology for processing and displaying large amounts of information is also developing rapidly. Accordingly, various flat panel displays have been developed to replace conventional cathode ray tubes (CRTs). Among these flat panel displays, an organic light-emitting diode (OLED) display, which can be manufactured in a thin-film structure and has low power consumption, is considered the next generation display device, capable of replacing liquid crystal displays (LCDs).

[0003] However, if the current density or driver voltage of an OLED display device is increased to raise the luminance, and this is due to degradation of the OLED, such as the degradation of an organic emissive material used in the OLED, the OLED's lifetime will be shortened. In particular, OLEDs fail to implement the wide color gamut required by ITU-R Recommendation BT.2020 (Rec.2020 or BT.2020), developed by the International Telecommunication Union (ITU) in relation to the 4K / UHD specification.

[0004] In recent years, efforts have been made to use quantum dots (QDs) in a display device. QDs are inorganic particles that emit light as electrons, in an unstable state, transition from a conduction band to a valence band. Among inorganic particles, QDs have a very high extinction coefficient and excellent quantum efficiency, and therefore emit strong fluorescence. Since an emission wavelength varies according to the QD size, light across the entire visible spectrum can be obtained by appropriately adjusting the QD size, thus realizing a wide range of colors. This means that when QDs are used in an emissive material layer (EML), the color purity of each pixel can be increased, and since white light, composed of red (R), blue (B), and green (G) light with high purity, can be achieved, the Rec. 2020 standard can be met.

[0005] A QD light-emitting diode (QLED) is developed using QDs and is known, for example, from US 2010 / 0 108 984 A1 or US 2017 / 0 271 604 A1. Fig. Figure 1 illustrates a bandgap energy diagram in a general QLED. Referring to Fig. 1 The general QLED has an anode and a cathode arranged opposite each other, a QD-containing EML arranged between the anode and the cathode, a hole injection layer (HIL) and a hole transfer layer (HTL) arranged between the anode and the EML, and an ETL arranged between the cathode and the EML.

[0006] The EML consists of nanoscale QDs and is formed, for example, by applying a solution containing QDs in a solvent to the HTL and then allowing the solvent to evaporate. Meanwhile, the HIL and HTL are configured to inject and transfer holes as positive charge carriers from the anode to the EML, and the ETL is configured to inject and transfer electrons as negative charge carriers from the cathode to the EML. To inject and transfer holes and electrons into the EML, each layer must be made of a material with a suitable bandgap energy. For example, the HIL can be made of poly(3,4-ethylenedioxythiophene)polystyrenesulfonate (PEDOT: PSS), the HTL can be made of poly(4-butylphenyldiphenylamine) (poly-TPD), and the ETL can be made of ZnO.

[0007] QDs can be applied to the HTL via a solution process, and an organic ligand is bound to a QD surface to uniformly disperse the QDs in a solvent used in the solution process. Conventionally, the organic ligand binding to the QD surface has a functional group with a specific charge. Accordingly, a charge carrier with a charge opposite to that of the functional group in the organic ligand can be rapidly transferred to the EML due to electrical attraction, while the transfer of a charge carrier with the same charge as that of the functional group in the organic ligand to the EML is delayed by electrical repulsion.

[0008] As described above, because the injection of holes and electrons into the EML in a conventional QLED is not balanced, the electrons and holes in QDs do not recombine in the EML. As a result, light emission occurs at the interface between the EML and a charge transfer layer, such as the HTL or ETL adjacent to the EML, and the luminous efficacy of the QLED is reduced. Furthermore, a high voltage must be applied to drive the LED, and therefore the QLED's drive voltage is increased.

[0009] Due to the van der Waals forces formed between a ligand chain bound to a QD surface and an organic solvent used in QD synthesis, a large amount of organic components remains in the EML coated with the synthesized QDs. Because of this high concentration of organic components, it is difficult to achieve a uniform thickness in the QD-containing EML. Furthermore, since the organic components remaining in the EML can penetrate into the adjacent ETL or the cathode, the boundary between the layers becomes blurred, making it difficult to form the ETL and the cathode. SUMMARY

[0010] Accordingly, the present disclosure relates to a QLED and a light-emitting display device incorporating it, which avoids one or more of the problems arising from limitations and disadvantages of the related technology.

[0011] One object of the present disclosure is to provide a QLED that can be operated at low voltage and has improved luminous efficacy, as well as a QD light-emitting device having this capability. Various embodiments provide a quantum dot according to claim 1. Further embodiments are described in the dependent claims.Various embodiments provide a quantum dot comprising a semiconductor nanocrystal or metal oxide core, a shell substantially or completely covering the semiconductor nanocrystal or metal oxide core, the shell having an outer surface, an X-type ligand comprising a functional group selected from the group consisting of a carboxylate group, a phosphate group and a thiolate group bonded to a first region of the outer surface, and an L-type ligand comprising a functional group selected from the group consisting of an amino group, a thiol group, a phosphine group and a phosphine oxide group bonded to a second region of the outer surface.

[0012] In some embodiments, the first region and the second region are respective hemispheres of the outer surface (where, for example, the outer surface is spherical).

[0013] Another objective of the present disclosure is to provide a QLED that is produced by effectively adjusting the thickness of an EML forming the light-emitting diode and simply forming a charge transfer layer and an electrode, and a QD light-emitting device comprising these.

[0014] According to one aspect of the present disclosure, the present disclosure provides a QLED having first and second electrodes facing each other; and an EML between the first electrode and the second electrode having QDs in which ligands are bound to the QD surface, wherein the ligands include X-type ligands that bind to a first surface region of the QD surface facing an electrode selected by the first and second electrodes, and L-type ligands that bind to a second surface region of the QD surface opposite the first surface region.

[0015] The X-type ligand can bind to the first surface region of the QD through a negatively charged functional group selected from the group consisting of a carboxylate group, a phosphonate group and a thiolate group.

[0016] The X-type ligand can, for example, be from one of the C5 to C 30 -derived fatty acids.

[0017] The L-type ligand can bind to the second surface region of the QD via a non-shared electron pair of a functional group selected from the group consisting of an amino group, a thiol group, a phosphine group and a phosphine oxide group.

[0018] As an example, the L-type ligand can be selected from the group consisting of linear or branched ligands C1 to C1. 10 -Alkylamines, alicyclic C4 to C8 amines, aromatic C5 to C 20 -Amines, linear or branched C1 to C 10 -Alkylphosphines, linear or branched C1 to C 10 -Alkylphosphine oxides and a combination thereof.

[0019] According to an exemplary embodiment, the QLED can further have a first charge transfer layer arranged between the first electrode and the EML, and a second charge transfer layer arranged between the second electrode and the EML.

[0020] In an exemplary embodiment, the first charge transfer layer can have an HTL and the second charge transfer layer can have an ETL.

[0021] In this case, the X-type ligand can be provided in an area of ​​the QD surface that is connected to the hole transfer layer, and the L-type ligand can be provided on a part of the QD surface that is connected to the electron transfer layer.

[0022] In another exemplary embodiment, the first charge transfer layer can have an electron transfer layer and the second charge transfer layer can have a hole transfer layer.

[0023] In this case, the L-type ligand can be provided in a part of the QD surface adjacent to the electron transfer layer, and the X-type ligand can be provided in a part of the QD surface adjacent to the hole transfer layer.

[0024] According to another aspect of the present disclosure, the present disclosure provides a QD light-emitting device comprising a substrate; the QLED described above, arranged on the substrate; and a driver element, arranged between the substrate and the QLED and connected to the QLED.

[0025] For example, the QD light-emitting device may include a QD light-emitting display device, but the present disclosure is not limited thereto. BRIEF DESCRIPTION OF THE DIFFERENT VIEWS OF THE DRAWINGS

[0026] The accompanying drawings, which are included to facilitate a better understanding of the revelation, are incorporated into this description and form a part of it, illustrating implementations of the revelation and, together with the description, serving to explain the principles of embodiments of the revelation. Fig. Figure 1 is a schematic diagram representing the band gap energy of materials forming an EML and a charge transfer layer in a general QLED. Fig. Figure 2 is a schematic diagram illustrating the procedure for synthesizing a QD in which different ligand types are bound to corresponding areas of the QD surface, from a QD to which a single ligand type is bound. Fig. Figure 2 shows QDs where the negative charge of the X-type ligand originates from a carboxylate and an L-type ligand is bound to the QD surface via a nitrogen atom forming an amino group. Fig. Figure 3 is a cross-sectional view schematically illustrating a light-emitting diode (LED) according to a first exemplary embodiment of the present disclosure, which has QDs in which different ligand types are bonded to specific regions of the QD surface. Below the cross-sectional view of the LED are shown EMLs: one consisting of a single layer of QDs and the other consisting of a double layer of QDs. Fig. Figure 4 is a cross-sectional view schematically illustrating an LED according to a second exemplary embodiment of the present disclosure, on which QDs are applied in which different ligand types are bound to specific regions of the QD surface. Below the cross-sectional view of the LED are shown EMLs: one consisting of a single layer of QDs and the other consisting of a double layer of QDs. Fig. Figure 5 is a cross-sectional view of a quantum dot light-emitting device as an example of a light-emitting device comprising an LED, according to an exemplary embodiment of the present disclosure. Fig. Figure 6 is a transmission electron microscope (TEM) image showing QDs according to an exemplary embodiment of the present disclosure, in which ligand types with different properties are bound to the QD surface. Fig. Figure 7 is a graph showing the result of a Fourier transform infrared (FT-IR) spectroscopy analysis for QDs synthesized according to an exemplary embodiment of the present disclosure, in which ligand types with different properties are bound to the QD surface. A result of the FT-IR analysis of QDs prepared according to a comparative example, in which only X-type ligands are bound to the QD surface, is also shown. Fig. 8A is a graph that represents a result of a thermogravimetric analysis (TGA) for conventional QDs where only X-type ligands are bound to the QD surface, and Fig. Figure 8B is a graph illustrating a TGA result of QDs according to the present disclosure, in which X-type ligands and L-type ligands are bound to two opposite parts on the QD surface. Fig. Figure 9 is a graph illustrating a result of time-of-flight secondary ion mass spectrometry (TOF-SIMS) for QDs synthesized according to an exemplary embodiment of the present disclosure, in which ligands with different properties are bound to the QD surface. Fig. 10A and Fig. 10B are TEM images that schematically represent the cross-sectional structures of EMLs produced by applying a single layer ( Fig. 10A) and a double layer ( Fig. 10B) of QDs synthesized according to an exemplary embodiment of the present disclosure, wherein ligands with different properties are bound to the QD surface. Fig. 11A and Fig. Figure 11B are TEM images schematically showing the cross-sectional structure of an LED having an EML formed by applying QDs synthesized according to an exemplary embodiment of the present disclosure, in which ligands with different properties are bound to the QD surface. Fig. Figure 11A illustrates the cross-sectional structure of an EML and a charge transfer layer, and Fig. Figure 11B illustrates the cross-sectional structure of an electrode. Additionally, the following is shown: Fig. 11A and Fig. 11B The image on the left shows an LED with an EML produced by applying QDs synthesized according to a comparative example in which only X-type ligands were bound to the surface, and the image on the right shows an LED having an EML produced by applying QDs synthesized according to the present disclosure in which ligands with different properties are bound to the QD surface. DETAILED DESCRIPTION

[0027] The present disclosure is described below with reference to the accompanying drawings, if necessary.

[0028] According to one aspect of the present disclosure, the present disclosure relates to a QLED on which QDs are applied, in which ligands with different properties and / or types are bound to specific areas of the QD surface. Fig. Figure 2 is a schematic diagram illustrating the procedure for synthesizing a QD in which a single ligand type is bound and a QD in which different ligand types are bound to specific regions of the QD surface.

[0029] As schematically in Fig. As illustrated in Figure 2, according to the present disclosure, if a ligand exchange with L-type ligands 44 occurs at QD 10A, only X-type ligands 42 (left side of Fig. 2) are bound to a part of the QD 10 surface, resulting in the synthesis of QD 10 to which different ligand types are bound to different surface regions. The right side of [image / diagram] shows an example. Fig. 2 of the QD 10 with a spherical shape, in which X-type ligands 42 are bound to the lower hemisphere of the QD surface and L-type ligands 44 are bound to the upper hemisphere of the QD surface, which is opposite the one to which X-type ligands 42 are bound.

[0030] In one exemplary embodiment, the QD 10A, located on the left side of Fig. 2 is shown, in which only the X-type ligands 42 are bound to the surface, by adding a metal precursor (e.g., a fatty acid ester of a metal) corresponding to a cation of a nucleus 20 to a high-temperature reactor and performing pyrolysis or hot injection to dissolve the precursor together with the fatty acid in an organic solvent (e.g., octadecene with a high boiling point) (e.g., colloidal QDs). When selenium (Se) or sulfur (S) is dissolved in an organic solvent such as alkylphosphine (e.g., tri-butylphosphine, tri-n-octylphosphine, tris(trimethylsilyl)phosphine, etc.) and introduced into the reactor, which contains the dissolved metal precursor at a nucleation temperature, nucleation of the precursor occurs, and the reaction precursor that did not participate in the nucleation additionally reacts with a nucleus surface, thereby growing a nucleus 20.

[0031] Subsequently, a precursor of shell 30 (e.g., a cationic metal precursor in which X-type ligands are bound to the precursor surface and a sulfur precursor dissolved in alkylphosphine), which is to grow, is additionally injected into the reactor, which has the core 20 of the QD. Therefore, the QD 10A with a heterologous core 20 / shell 30 structure, in which the outer surface of the core 20 is surrounded by the shell 30 (an inorganic layer) in which X-type ligands 42 are bound to the shell surface, can be synthesized without further nucleation.Depending on the reactivity and injection rate, ligand type, reaction temperature and the like of the reaction precursors forming the nucleus 20 and / or shell 30, a growth degree, crystal structure and the like of the nucleus 20 / shell 30 forming the QD 10A can be adjusted, and thus light emission at different wavelengths can be induced according to the setting of the band gap energy.

[0032] Here, the X-type ligand 42 refers to a negatively charged (-) organic ligand across the entire surface area of ​​QD 10A, which is attached to the surface of QD 10A by a negatively charged functional group, selected from the group consisting of, for example, a carboxylate group (-COO). -), a phosphonate group and a thiolate group. In an exemplary embodiment, the X-type ligand 42 can bind to the surface of QD 10A via a carboxylate group. In particular, the X-type ligand 42 can be bound by a saturated or unsaturated C5 to C 30 -Fatty acid, preferably a saturated or unsaturated C8 to C 20 -fatty acid. In particular, the X-type ligand 42 can be derived from a saturated or unsaturated fatty acid such as octanoic acid (caprylic acid, CH3(CH2)6COOH), a decanoic acid (CH3(CH2)8COOH), a dodecanoic acid (lauric acid, CH3(CH2) 10 COOH), a myristic acid (1-tetradic acid, CH3(CH2) 12 COOH), palmitic acid (n-hexadecanoic acid, CH3(CH2) 14 COOH), a stearic acid (n-octadecanoic acid), CH3(CH2) 16COOH) or an oleic acid (cis-9-octadecanoic acid, (CH3(CH2)7CH=CH(CH2)7COOH)). In one embodiment, the X-type ligand further comprises a saturated or unsaturated C5-C 30 -hydrocarbon chain. In a more specific embodiment, the X-type ligand has one of the following structures: where n is an integer in the range of 6 to 16, m is an integer in the range of 4 to 9, p is an integer in the range of 4 to 9, and X is a carboxylate group, a phosphate group, or a thiolate group.

[0033] In this case, a negative charge, for example a carboxylate group (-COO⁻), is present. - ), which forms the X-type ligand 42, with a metal cation (M + ), which the shell 30 through a weak electrical interaction (M + : - OOC) forms, coupled. When the QD 10A, in which the negatively charged X-type ligands 42 are bound to its surface, is in an EML (see Fig. 3 and Fig. 4) a QD light-emitting diode (QLED; 100 and 200 in Fig. When 3 or 4) is used, the following problems occur.

[0034] Since the X-type ligands 42 have a negative charge, holes, i.e. positive charge carriers, can be rapidly injected and transferred to the surface of the QD 10A, which is a light-emitting particle formed in an EML, by electrical attraction (see Fig. 3) On the other hand, the injection and transfer of electrons, i.e. negative charge carriers having the same charge as a charge formed in the X-type ligand 42, onto the surface of the QD 10A formed in the EML (see Fig. 3) delayed by electrical repulsion. Since the injection of holes and electrons is not balanced, the electrons and holes do not recombine at QD 10A in the EML, but at the interface between the EML (see Fig. 3) and an ETL 164 (see Fig. 3) Therefore, in the EML (see Fig. 3) An exciton is not sufficiently bound but is quenched, and therefore the luminous efficacy of the LED is reduced. Since a high voltage is also required to drive the LED, the LED's driver voltage is increased.

[0035] When QD 10A is synthesized, an alkyl fatty acid is additionally used as a source for the X-type ligand 42, and octadecene, an organic solvent, is used as the solvent. Due to the strong van der Waals force between the alkyl chain forming the fatty acid and octadecene, the solvent component is not completely removed. Therefore, in addition to the X-type ligand 42 component, a large amount of organic components will remain in the fully synthesized QD 10A. If the EML (see Fig. 3) if a coating of QD 10A is formed in which a large amount of organic components remain, it is difficult to produce a uniform coating of QD 10A, and thus it is difficult to obtain an EML (see Fig. 3) to form with a uniform thickness.

[0036] Furthermore, a large amount of the organic components remain in the EML (see Fig. 3), if a second charge transfer layer 160 (see Fig. 3) and a second electrode 120 (see Fig. 3) be stacked on an upper surface of the EML (see Fig. 3) The remaining organic components penetrate the second charge transfer layer and / or the second electrode. Therefore, the boundaries within the second charge transfer layer and / or between the second charge transfer layer and the second electrode become blurred, and the layers lose their original properties. For this reason, it is difficult when the LED 100 (see Fig. 3) is produced using the QD 10A in which the X-type ligand 42 is bonded to the entire QD surface, a charge transfer layer (CTL), for example the second charge transfer layer 160 (see Fig. 3), and an electrode, for example the second electrode 120 (see Fig. 3) to laminate with desired shapes or thicknesses.

[0037] Accordingly, in the present disclosure, a substrate 50 is coated with the QD 10A by binding the X-type ligands 42, previously dispersed in an organic solvent, to the QD surface, and subsequently the L-type ligands 44 are dispersed in a solvent. Since the L-type ligands 44 cannot react with the QD 10A and ligand exchange does not occur when the substrate 50 (the lower hemisphere region of the QD 10A surface) is dispersed in a solvent, the following applies: Fig. 2; first area) blocked part, the X-type ligands 42 remain bound to the surface of the QD 10 as described above.

[0038] The L-type ligand 44 refers to a neutral organic ligand that binds to the surface of QD 10 via a non-shared electron pair. For example, the L-type ligand 44 can bind to the QD surface via a non-shared electron pair of a functional group selected from the group consisting of an amino group, a thiol group, a phosphine group, and a phosphine oxide group. In another example, the L-type ligand 44 binds to a metal cation (M + ; e.g., Zn + ) on the surface of the QD 10 by a coordination bond shown below, using a non-shared electron pair of a nitrogen atom (N) forming an amino group. N:+M + →7N + :M

[0039] In an exemplary embodiment, the L-type ligand 44 can be a type of ligand that exhibits no or almost no attraction caused by interaction with an organic solvent (e.g., octadecene) used in the synthesis of QD 10. In this case, since some X-type ligands 42 are replaced by the L-type ligands 44, the bond between the QD and an organic component originating from the organic solvent is weakened, and thus the content of organic components remaining in the finished synthesized QD 10 can be reduced.

[0040] For example, the L-type ligand 44 may be selected from the group consisting of linear or branched C1 to C 10-Alkylamines (e.g. a monovalent, divalent or trivalent alkylamine) and preferably linear or branched C1 to C5 alkylamines, alicyclic C4 to C8 amines and preferably alicyclic C5 to C8 amines, aromatic C5 to C 20 -Amines and preferably aromatic C5- to C 10 -Amines, linear or branched C1- to C 10 -Alkylphosphines (e.g. monovalent, divalent or trivalent alkylphosphines) and preferably linear or branched C1- to C5-alkylphosphines, linear or branched C1- to C 10 -Alkylphosphine oxides (e.g. monovalent, divalent or trivalent alkylphosphine oxides) and preferably linear or branched C1 to C5 alkylphosphine oxides and a combination thereof.

[0041] In one exemplary embodiment, the L-type ligands comprise 44 tertiary amines such as tris(2-aminoethyl)amine (TAEA) and tris(2-aminomethyl)amine; alkyl polyamines such as N-butyl-N-ethylethane-1,2-diamine, ethylenediamine and pentaethylenehexamine; alicyclic polyamines such as cyclohexane-1,2-diamine and cyclohexene-1,2-diamine; aromatic amines such as 2,3-diaminopyridine and a combination thereof, but the present disclosure is not limited thereto.

[0042] In contrast to the X-type ligands 42, which are characterized by a weak electrical interaction (M + : - OOC) bind to the QD surface 10A, the L-type ligands 44 can bind strongly to the surface of QD 10 via coordination bonding using unshared electron pairs. Accordingly, in the region of QD surface 10A not covered by the substrate 50 (the upper hemisphere region of QD surface 10A in Fig. 2; second region) is blocked, inducing a ligand exchange reaction to replace the X-type ligand 42, which is weakly bound to the QD surface 10A, with the L-type ligand 44, which binds strongly to it. As a result of such a ligand exchange reaction, QD 10s can be synthesized in which the X-type ligand 42 binds to the first surface region and the L-type ligand 44 binds to the second surface region, which is a part of the QD 10 surface opposite the first surface region.

[0043] According to the present disclosure, the use of the QD 10 according to the present disclosure, in which the X-type ligand 42, which has a negative charge, binds to the first surface region of the surface of the QD 10 and the L-type ligands 44, which have a positive charge, bind to the second surface region, which is a part of the QD 10 surface opposite the first surface region, brings the EML (see Fig. 3) to form, the following advantages.

[0044] Holes, i.e. positive charge carriers, can be rapidly injected and placed on the surface of the QD 10 in the EML (see Fig. 3) due to the electrical attraction with the X-type ligand 42, which has an opposite charge. At the same time, electrons, i.e., negative charge carriers, can be rapidly injected and transferred to the surface of QD 10 in the EML (see Fig. 3) Due to electrical attraction with the L-type ligand 44, which has an opposite charge, in the second surface region of QD 10, the holes and electrons are transferred. Since the holes and electrons at QD 10 in the EML are rapidly balanced and recombinated, exciton quenching is reduced and the LED's luminous efficacy is improved. Because exciton recombination at the interface between the EML and an adjacent charge transfer layer (e.g., ETL), caused by the unbalanced injection of holes and electrons, is prevented, the LED can be operated at a low voltage.

[0045] When the X-type ligands 42 are removed from the QD 10 due to a ligand exchange between the X-type ligands 42 and the L-type ligands 44, the organic component (a component derived from an organic solvent such as octadecene), which previously remained bound to the X-type ligands 42 due to van der Waals forces, exhibits a weaker van der Waals force with the L-type ligands 44. Consequently, the organic component no longer binds to the L-type ligands 44 and is removed from the surface of the QD 10. Since the content of the remaining organic components in the fully synthesized QD 10 is reduced, the QDs 10 can be applied uniformly to form the EML (see Fig. 3) and thus a thickness of the EML (see Fig. 3) be adjusted evenly.

[0046] While the second charge transfer layer 160 (see Fig. 3) and the second electrode 120 (see Fig. 3) on an upper surface of the EML (see Fig. 3) When stacked, the organic components remaining in the EML do not penetrate the second charge transfer layer and the second electrode. Because the penetration of the organic components is prevented, the boundary between the second charge transfer layer and the second electrode can be clearly distinguished, and the original properties of the layers can be maintained. Therefore, a CTL, for example the second charge transfer layer 160 (see Fig. 3), and an electrode, for example the second electrode 120 (see Fig. 3) can be stacked in desired shapes or thicknesses.

[0047] Next, the structure of QD 10 synthesized according to the present disclosure is described. In one exemplary embodiment, QD 10 can have a homogeneous structure. In another exemplary embodiment, QD 10 can have a heterologous structure comprising a core 20 and a shell 30. Here, the shell 30 can be a single shell or multiple concentric shells.

[0048] As an example, QD 10 can have a heterologous structure with: the core 20, which is located in the center of QD 10 to emit light; and the shell 30, which covers a surface of the core 20 to protect it; and the ligands 42 and 44, which can cover a surface of the shell 30 to disperse the QD 10 in a solvent. For example, QD 10 can have a type 1 core / shell structure, in which the energy band gap of the core 20 component is surrounded by the energy band gap of the shell 30, and electrons and holes are transferred to the core 20 and recombine within the core 20, which is a phosphor, thereby emitting energy as light.

[0049] If the QDs 10 have a type 1 core / shell structure, the core 20 is the part where luminescence essentially occurs, and the emission wavelength of the QD 10 is determined depending on the size (e.g., the diameter) of the core 20. To exploit a quantum confinement effect, it is necessary that the core 20 has a smaller size than the exciton Bohr radius according to a material and exhibits an optical band gap of the corresponding size.

[0050] Meanwhile, shell 30, which forms QD 10, promotes the quantum confinement effect of nucleus 20 and determines the stability of QD 10. Atoms exposed on the surface of the simply structured colloidal QDs 10, unlike internal atoms, have lone pairs of electrons that do not participate in chemical bonding. Since the energy levels of these surface atoms lie between the conduction band edge and the valence band edge of QD 10, the surface atoms can trap charges, forming surface defects. Due to a non-radiative recombination process of excitons caused by these surface defects, the light yield of QDs 10 can be reduced, and the chemical composition of QDs 10 can be modified by the reaction between the trapped charges and external oxygen and components, or electrical / optical properties of QDs 10 can be permanently lost.

[0051] Therefore, in an exemplary embodiment, the QD 10 can have a heterologous core 20 / shell 30 structure. To effectively form the shell 30 on the surface of the core 20, it is necessary that the lattice constant of the material forming the shell 20 be similar to that of the material forming the core 20. Since the surface of the core 20 is surrounded by the shell 30, oxidation of the core 20 can be prevented, thereby increasing the chemical stability of the QD 10. Furthermore, the loss of excitons caused by the surface trapping site on the surface of the core 20 can be minimized, and energy loss due to molecular vibration can be prevented, thus increasing the quantum yield.

[0052] The QD 10 can be a semiconductor nanocrystal or metal oxide particle exhibiting a quantum confinement effect. For example, the QD 10 can consist of group II-VI, III-V, IV-VI, and I-III-VI semiconductor nanocompounds.In particular, the QD 10 can be a core 20 / shell 30-structured nanocrystal, wherein the core 20 and / or the shell 30 forming the QD 10 can be a group II-VI compound semiconductor nanocrystal, for example CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgTe and / or a combination thereof; a group III-V compound semiconductor nanocrystal, for example GaP, GaAs, GaSb, InP, InAs, InSb and / or a combination thereof; a group IV-VI compound semiconductor nanocrystal, for example PbS, PbSe, PbTe and / or a combination thereof; may be a group I-III-VI compound semiconductor nanocrystal, for example AgGaS2, AgGaSe2, AgGaTe2, CuInS2, CuInSe2, CuGaS2, CuGaSe2 and / or a combination thereof; may be a metal oxide nanoparticle, for example ZnO, TiO2 and / or a combination thereof; or may be CdSe / ZnSe, CdSe / ZnS, CdS / ZnSe, CdS / ZnS, ZnSe / ZnS, InP / ZnSZnO / MgO and / or any combination thereof.The semiconductor nanoparticle can be undoped or doped with a rare earth element, for example Eu, Er, Tb, Tm or Dy or any combination thereof, or can be doped with a transition metal element, for example Mn, Cu, Ag or Al or any combination thereof.

[0053] For example, core 20 of QD 10 can be selected from the group consisting of ZnSe, ZnTe, CdSe, CdTe, InP, ZnCdS, Cu x In 1-x S, Cu x In 1-x Se, Ag x In 1-x S and a combination thereof. Additionally, shell 30 of QD 10 can be selected from the group consisting of ZnS, GaP, CdS, ZnSe, CdS / ZnS, ZnSe / ZnS, ZnS / ZnSe / CdSe, GaP / ZnS, CdS / CdZnS / ZnS, ZnS / CdSZnS, Cd x Zn 1-x S and a combination thereof. Optionally, the QD 10 can be an alloy QD (e.g., CdS). x See 1-x , CdSe x Te 1-x or Zn x CD 1-xSe), for example, a homogeneous alloy QD or a gradient alloy QD. In some embodiments, the QD has a substantially spherical shape, the surface area of ​​which has two halves or two hemispheres, namely a first hemisphere and a second hemisphere of the spherical shape. In some embodiments, the first area of ​​the outer surface is the first hemisphere and the second area of ​​the outer surface is the second hemisphere.

[0054] The following describes an LED according to the present disclosure which has QDs to which different types of ligands are bound on the QD surface. Fig. Figure 3 is a cross-sectional view schematically illustrating an LED according to a first exemplary embodiment of the present disclosure, which has QDs to which different ligand types are bound to specific regions of the QD surface. As in Fig. As illustrated in Figure 3, the QLED 100, according to an exemplary embodiment of the present disclosure, has a first electrode 110, a second electrode 120 arranged opposite the first electrode 110, and an emission layer 130 arranged between the first electrode 110 and the second electrode 120, which includes an EML 150. As an example, the emission layer 130 can further include a first charge transfer layer 140 arranged between the first electrode 110 and the EML 150, and a second charge transfer layer 160 arranged between the EML 150 and the second electrode 120.

[0055] In this exemplary embodiment, the first electrode 110 can be an anode, for example a hole injection electrode. The first electrode 110 can be formed on a substrate made of glass or a polymer (in Fig. 3 not shown). For example, the first electrode 110 can be a doped or undoped metal oxide, such as indium tin oxide (ITO), indium zinc oxide (IZO), indium tin-zinc oxide (ITZO), indium copper oxide (ICO), tin oxide (SnO2), indium oxide (In2O3), cadmium:zinc oxide (Cd:ZnO), fluorine:tin oxide (F:SnO2), indium:zinc oxide (In:SnO2), gallium:tin oxide (Ga:SnO2), or aluminum:zinc oxide (Al:ZnO; AZO). Optionally, the first electrode 110 can consist of a metal or non-metal material containing nickel (Ni), platinum (Pt), gold (Au), silver (Ag), iridium (Ir), or a carbon nanotube (CNT), other than a metal oxide described above.

[0056] In this exemplary embodiment, the second electrode 120 can be a cathode, for example, an electron injection electrode. For example, the second electrode 120 can consist of Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF₂ / Al, CsF / Al, CaCO₃ / Al, BaF₂ / Ca / Al, Al, Mg, Au:Mg, or Ag:Mg. For example, both the first electrode 110 and the second electrode 120 can be stacked such that they have a thickness of 30 to 300 nm.

[0057] In an exemplary embodiment, in the case of a bottom-emission type LED, the first electrode 110 can consist of a transparent conductive metal such as ITO, IZO, ITZO or AZO, and the second electrode 120 can consist of Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF2 / Al, Al, Mg or an Ag:Mg alloy.

[0058] The first charge transfer layer 140 is arranged between the first electrode 110 and the EML 150. In this exemplary embodiment, the first charge transfer layer 140 can be a hole transfer layer that provides holes to the EML 150. For example, the first charge transfer layer 140 can have a HIL 142 formed adjacent to the first electrode 110 between the first electrode 110 and the EML 150, and an HTL 144 formed adjacent to the EML 150 between the first electrode 110 and the EML 150.

[0059] The HIL 142 facilitates the injection of holes from the first electrode 110 into the EML 150. As an example, the HIL 142 can consist of an organic material selected from the group consisting of poly(ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS), 4,4',4''-tris(diphenylamino)triphenylamine (TDATA) doped with tetrafluorotetracyanoquinodimethane (F4-TCNQ), a p-doped phthalocyanine (e.g., F4-TCNQ-doped zinc phthalocyanine (ZnPc)), F4-TCNQ-doped N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4''-diamine (α-NPD), hexaazatriphenylenehexanitrile (HAT-CN), and a combination thereof; however, the present disclosure is not limited thereto. For example, the dopant, such as F4-TCNQ, can be used to dope a host at a concentration of 1 to 30 wt% based on the host's weight. The HIL 142 can be omitted depending on the structure and type of the LED 100.

[0060] The HTL 144 transports holes from the first electrode 110 to the EML 150. The HTL 144 can be made of an inorganic or an organic material. If HTL 144 is made of an organic material, for example, it can be made of an organic material selected from the group consisting of arylamines, such as 4,4'-N-N'-dicarbazolylbiphenyl (CBP), N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-biphenyl-4,4''-diamine (α-NPD), N,N'-diphenyl-N,N'-bis(3-methylphenyl)-(1,1'-biphenyl)-4,4'-diamine (TPD), N,N'-bis(3-methylphenyl)-N,N'-bis(phenyl)-spiro (Spiro-TPD), N,N'-di(4-(N,N'-diphenylamino)phenyl)-N,N'-diphenylbenzidine (DNTPD), 4,4',4'-tris(N-carbazolyl)-triphenylamine (TCTA), tris(3-methylphenylphenylamino)-triphenylamine (m-MTDATA), poly[(9,9'-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-sec-butylphenyl)diphenylamine))] (TFB), and poly(4-)butylphenyldiphenylamine) (poly-TPD); a polyaniline; a polypyrrole;Poly(para)phenylenevinylene and derivatives thereof, such as poly(phenylenevinylene) (PPV), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) and poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-1,4-phenylenevinylene] (MOMO-PPV); copper phthalocyanine; aromatic tertiary amines or polynuclear aromatic tertiary amines; a 4,4'-bis(p-carbazolyl)-1,1'-biphenyl compound; N,N,N',N'-tetraarylbenidine; PEDOT:PSS and derivatives thereof; poly(N-vinylcarbazole) (PVK) and derivatives thereof; a polymethacrylate and derivatives thereof; poly(9,9-octylfluorene) and derivatives thereof; poly(spirofluorene) and derivatives thereof; N,N'-Di(naphthalen-1-yl)-N,N'-diphenylbenzidine (NPB); Spiro-NPB; and a combination thereof.

[0061] If the HTL 144 consists of an inorganic material, the HTL 144 may consist of an inorganic material selected from the group consisting of a metal oxide such as NiO, MoO3, Cr2O3, Bi2O3 or a p-type ZnO; non-oxidized equivalents such as copper thiocyanate (CuSCN), Mo2S or p-type GaN; and a combination thereof.

[0062] While the first charge transfer layer 140 in Fig. 3 is divided into HIL 142 and HTL 144, which can be found in Fig. Figure 3 illustrates that the first charge transfer layer 140 can be formed as a single layer. For example, the first charge transfer layer 140 can consist only of the HTL 144 without the HIL 142, or it can be formed by doping the organic hole-transporting material described above with a hole injection material (e.g., PEDOT:PSS).

[0063] The first charge transfer layer 140, comprising the HIL 142 and the HTL 144, can be formed by a process selected from vacuum deposition processes, such as vacuum vapor deposition and sputtering, and solution processes, such as centrifugal coating, drop coating, dip coating, spray coating, roller coating, gradient coating, casting, screen printing, and inkjet printing, or a combination of these processes. For example, the thicknesses of the HIL 142 and the HTL 144 can be 10 to 200 nm, and preferably 10 to 100 nm, but the present disclosure is not limited thereto.

[0064] The EML 150 can be a layer filled with the electroluminescent nanoparticles according to the present disclosure, i.e., the QDs 10. The QDs 10 can be formed in a heterologous structure consisting of a core 20, which is a phosphor, and a shell 30 surrounding the core 20, and various ligand types 42 and 44 can bind to the surface of the shell 30. Here, the EML 150 can consist of a single layer of QDs 10, as shown in Fig. 3(a) is shown or a multilayer consisting of two or more layers of QDs 10, as shown in Fig. 3(b) is shown.

[0065] In an exemplary embodiment, the EML 150 can be formed by applying a dispersion containing the electroluminescent nanoparticles (i.e., QDs 10) in a solvent to the first charge transfer layer 140 using a solution process and subsequent evaporation of the solvent. The EML 150 can be formed using a solution process selected from, for example, centrifugal coating, drop coating, dip coating, spray coating, roller coating, gradient coating, casting, screen printing, and inkjet printing, or a combination thereof.

[0066] In one exemplary embodiment, the EML 150 can comprise electroluminescent nanoparticles (i.e., QDs 10) exhibiting photoluminescence (PL) properties at 440 nm, 530 nm, and 620 nm, thereby producing a white LED. Optionally, the EML 150 can comprise electroluminescent nanoparticles (i.e., QDs 10) emitting red, green, and blue light, with each QDs 10 capable of independently emitting light of one of the colors.

[0067] As described above, the different ligand types 42 and 44 can bind to the surface of QD 10. In this exemplary embodiment, the X-type ligands 42, with a negatively charged functional group, are arranged in a region of the surface of QD 10 opposite the first electrode 110, which is involved in the injection and transfer of holes; that is, charge carriers with a charge opposite to that of the X-type ligands 42. That is, the X-type ligands are arranged such that they face the interface between the EML 150 and the first charge transfer layer 140. Furthermore, the L-type ligands 44, with a positively charged functional group, are arranged in a region of QD 10 opposite the second electrode 120, which is involved in the injection and transfer of electrons; that is, charge carriers with a charge opposite to that of the L-type ligands 44.This means that the L-type ligands 44 are arranged such that they face the interface between the EML 150 and the second charge transfer layer 160.

[0068] Meanwhile, the second charge transfer layer 160 is arranged between the EML 150 and the second electrode 120. In this exemplary embodiment, the second charge transfer layer 160 can be an electron transfer layer that supplies an electron to the EML 150. In an exemplary embodiment, the second charge transfer layer 160 can have an electron injection layer (EIL) 162, which is arranged adjacent to the second electrode 120 between the second electrode 120 and the EML 150, and an ETL 164, which is arranged adjacent to the EML 150 between the second electrode 120 and the EML 150.

[0069] The EIL 162 is designed to easily inject electrons from the second electrode 120 into the EML 150. For example, the EIL 162 can consist of a material in which a metal, such as Al, Cd, Cs, Cu, Ga, Ge, In or Li, is doped or bonded with fluorine, or of a metal oxide (e.g. titanium dioxide (TiO2), zinc oxide (ZnO), zirconium oxide (ZrO), tin oxide (SnO2), tungsten oxide (WO3) or tantalum oxide (Ta2O3)) undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs, Cu or the like.

[0070] The ETL 164 is designed to transport electrons to the EML 150. The ETL 164 can be made of an inorganic and / or an organic material. The ETL 164 can consist of an inorganic material selected from the group consisting of metal / nonmetal oxides (e.g., titanium dioxide (TiO2), zinc oxide (ZnO), zirconium oxide (ZrO), tin oxide (SnO2), tungsten oxide (WO3), tantalum oxide (Ta2O3), hafnium oxide (HfO3), aluminum oxide (Al2O3), zirconium silicon oxide (ZrSiO4), barium titanium oxide (BaTiO3), and barium zirconium oxide (BaZrO3)), which are undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs, or Cu; semiconductor particles (e.g., CdS, ZnSe, and ZnS), which are undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs, or Cu; a nitride, for example, Si3N4; and a combination thereof.

[0071] Alternatively, ETL 164 can consist of an organic material selected from the group consisting of an oxazole-based compound, an isooxazole-based compound, a triazole-based compound, an isothiazole-based compound, an oxadiazole-based compound, a thiadiazole-based compound, a phenanthroline-based compound, a perylene-based compound, a benzoxazole-based compound, a benzothiazole-based compound, a benzimidazole-based compound, a triazine-based compound, and an aluminum complex.In particular, the organic material that can be used to form ETL 164 can be selected from the materials including 3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), bathocuproin (2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; BCP), 2,2',2''-(1,3,5-benzenetriyl)-tris(1-phenyl)-1-H-benzimidazole; TPBi), Tris (S-hydroxyquinoline)aluminium (Alq3), bis(2-methyl-8-quinolinato)-4-phenylphenolatealuminium (III) (Balq), bis(2-methylquinolinato)(triphenylsiloxy)aluminium(III) (Salq) and a combination thereof, but the present disclosure is not limited thereto.

[0072] Similar to the first charge transfer layer 140, although Fig. Figure 3 illustrates the second charge transfer layer 160 as a double layer comprising ETL 162 and ETL 164; the second charge transfer layer 160 can also be formed as a single layer of ETL 164. Additionally, the second charge transfer layer 160 can be formed as a single layer of ETL 164, composed of a mixture of cesium carbonate with the electron-transporting inorganic material described above.

[0073] The second charge transfer layer 160, comprising the EIL 162 and / or the ETL 164, can be formed using a solution coating process, for example centrifugal coating, drop coating, dip coating, spray coating, roller coating, gradient coating, casting, screen printing, and inkjet printing, or a combination thereof. For example, both the EIL 162 and the ETL 164 can be stacked with a thickness of 10 to 200 nm, and preferably 10 to 100 nm.

[0074] For example, if a hybrid CTL is introduced in which the HTL 144 of the first charge transfer layer 140 is formed from an organic material and the second charge transfer layer 160 is formed from an inorganic material, or in which the HTL 144 is formed from an inorganic material and the second charge transfer layer 160 is formed from an organic material, the luminescence properties of the QLED 100 can be improved.

[0075] If, on the other hand, holes are transferred through the EML 150 to the second electrode 120, or electrons are transported through the EML 150 to the first electrode 110, the lifetime and efficiency of the diode can be reduced. To prevent such a reduction, the QLED 100, according to an exemplary embodiment of the present disclosure, can have at least one exciton blocking layer arranged adjacent to the EML 150.

[0076] For example, according to an exemplary embodiment of the present disclosure, the QLED 100 can have an electron blocking layer (EBL) suitable for controlling and preventing the transfer of electrons between the HTL 144 and the EML 150.

[0077] For example, EBL can consist of TCTA, Tris[4-(diethylamino)phenyl]amine), N-(Biphenyl-4-yl)-9,9-dimethyl-N-(4-(9-phenyl-9H)-Carbazol-3-yl)phenyl)-9H-fluoren-2-amine, Tri-p-tolylamine, 1,1-Bis(4-(N, N'-di(p-tolyl)amino)phenyl)cyclohexane (TAPC), m-MTDATA, 1,3-Bis(N-carbazolyl)benzene (mCP), 3,3'-Bis(N-carbazolyl)-1,1'-biphenyl (mCBP), Poly-TPD, copper phthalocyanine (CuPc), DNTPD and / or 1,3,5-Tris[4-(diphenylamino)phenyl]benzene (TDAPB).

[0078] Additionally, a hole-blocking layer (HBL) can be formed as a second exciton-blocking layer between the EML 150 and the ETL 164, thereby preventing the transfer of holes between the EML 150 and the ETL 164. In an exemplary embodiment, a material for the HBL can be a derivative of an oxadiazole-based compound, a triazole-based compound, a phenanthroline-based compound, a benzoxazole-based compound, a benzothiazole-based compound, a benzimidazole-based compound, a triazine-based compound, or the like, which can be used in the ETL 164.

[0079] For example, the HBL can consist of 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), BAlq, Alq3, PBD, Spiro-PBD and / or Liq, which has a lower highest occupied molecular orbital (HOMO) energy level than the material used for the EML 150.

[0080] As described above, according to this exemplary embodiment, different types of ligands bind to the surface of QD 10, which is an electroluminescent nanoparticle forming EML 150. In EML 150, the negatively charged X-type ligands 42 are arranged in a region of the QD surface facing the first electrode 110, which is involved in the generation, injection, and transfer of holes carrying the opposite charge to that of the X-type ligands 42. In particular, the X-type ligands 42 are arranged to face the interface between EML 150 and HTL 144 in the first charge transfer layer 140.On the other hand, in the EML 150, the L-type ligands 44, which exhibit a positive charge, are arranged in a portion of the QD surface facing the second electrode 120, which is involved in the generation, injection, and transfer of electrons having the opposite charge to that of the L-type ligand 44. In particular, the L-type ligands 44 are arranged such that they face the interface between the EML 150 and the ETL 164 in the second charge transfer layer 160.

[0081] Holes, i.e., positive charge carriers, can be rapidly transported to the surface of the QD 10 forming the EML 150, due to the X-type ligands 42, which exhibit a charge opposite to that of the holes. Simultaneously, electrons, which are negative charge carriers, can be rapidly transported to the surface of the QD 10 deposited in the EML 150, since the L-type ligands 44 have a charge opposite to that of the electrons. Because the holes and electrons in the EML 150 are balanced and quickly recombine, the LED 100 can have improved luminous efficacy and operate at a lower voltage.

[0082] Furthermore, since the L-type ligands 44 bind to the surface of the QD 10 by replacing the X-type ligands 42 without interaction with an organic component, the QD 10 according to the present disclosure retains a smaller amount of organic components compared to the QD 10A, which consists only of the X-type ligands 42 (see Fig. 2) Accordingly, the QDs 10 can be applied uniformly, and thus the EML 150 can be controlled to have a uniform thickness. If, in addition, the second charge transfer layer 160 and the second electrode 120 are stacked on the EML 150, the organic components do not penetrate the second charge transfer layer 160 and the second electrode 120. Therefore, the boundary between the second charge transfer layer 160 and the second electrode 120 can be clearly distinguished, and the second charge transfer layer 160 and the second electrode 120 can be formed with desired shapes or thicknesses.

[0083] Meanwhile, in Fig. Figure 3 illustrates the QLED with a normal structure, where the HTL is located between the first electrode with a relatively low work function and the EML, and the ETL is located between the second electrode with a relatively high work function and the EML. The QLED can have an inverted structure instead of the normal structure, as will be described later.

[0084] Fig. Figure 4 is a cross-sectional view schematically illustrating a QLED with an inverted structure according to a second exemplary embodiment of the present disclosure, on which QDs are deposited in which different ligand types are bound to specific regions of the QD surface. As in Fig. As shown in Figure 4, the QLED 200 according to the exemplary embodiment of the present disclosure has a first electrode 210, a second electrode 220 arranged opposite the first electrode 210, and an emission layer 230 arranged between the first electrode 210 and the second electrode 220, which includes an EML 250. The emission layer 230 may further include a first charge transfer layer 240 arranged between the first electrode 210 and the EML 250, and may include a second charge transfer layer 260 arranged between the second electrode 220 and the EML 250.

[0085] The first electrode 210 can be a cathode, for example, an electron injection electrode. For example, the first electrode 210 can consist of a doped or undoped metal oxide, such as ITO, IZO, ITZO, ICO, SnO2, In2O3, Cd:ZnO, F:SnO2, In:SnO2, Ga:SnO2 and AZO, or of a material containing Ni, Pt, Au, Ag, Ir or a CNT, with the exception of the metal oxide described above.

[0086] The second electrode 220 can be an anode, for example, a hole injection electrode. For example, the second electrode 220 can be Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF₂ / Al, CsF / Al, CaCO₃ / Al, BaF₂ / Ca / Al, Al, Mg, Au:Mg, or Ag:Mg. For example, both the first electrode 210 and the second electrode 220 can be stacked with a thickness of 30 to 300 nm.

[0087] In this exemplary embodiment, the first charge transfer layer 240 can be an electron transfer layer that provides an electrode to the EML 250. In an exemplary embodiment, the first charge transfer layer 240 has an EIL 242, which is arranged adjacent to the first electrode 210 between the first electrode 210 and the EML 250, and an ETL 244, which is arranged adjacent to the EML 250 between the first electrode 210 and the EML 250.

[0088] The EIL 242 can consist of a material in which a metal such as Al, Cd, Cs, Cu, Ga, Ge, In or Li is doped or bonded with fluorine, or of a metal oxide (e.g. TiO2, ZnO, ZrO, SnO2, WO3 or Ta2O3) that is undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs or Cu.

[0089] The ETL 244 can consist of an inorganic and / or an organic material. If the ETL 244 is formed from an inorganic material, the ETL 844 can be formed from an inorganic material selected from the group consisting of metal / nonmetal oxides such as TiO2, ZnO, ZrO, SnO2, WO3, Ta2O3, HfO3, Al2O3, ZrSiO4, BaTiO3, and BaZrO3, undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs, or Cu; semiconductor particles such as CdS, ZnSe, and ZnS, undoped or doped with Al, Mg, In, Li, Ga, Cd, Cs, or Cu; a nitride, for example Si3N4; and a combination thereof.

[0090] If ETL 244 is formed from an organic material, it can be formed from an organic material such as an oxazole-based compound, an isooxazole-based compound, a triazole-based compound, an isothiazole-based compound, an oxadiazole-based compound, a thiadiazole-based compound, a perylene-based compound, or an aluminum complex. In particular, the organic material that can be used to form ETL 244 can be an organic material selected from the group consisting of TAZ, BCP, TPBi, Alq3, Balq, Salq, and a combination thereof, but the present disclosure is not limited to these.

[0091] The first charge transfer layer 240 can be formed as a single layer of ETL 244. Alternatively, the first charge transfer layer 240 can be formed as a single layer of ETL 244, which is formed by mixing cesium carbonate with the electron-transporting inorganic material described above. For example, both ETL 242 and ETL 244 can be stacked to a thickness of 10 to 200 nm, preferably 10 to 100 nm.

[0092] The EML 250 can be a layer filled with the electroluminescent nanoparticles according to the present disclosure, i.e., the QDs 10. The QDs 10 can be formed in a heterologous structure consisting of a core 20, which is a phosphor, and a shell 30 surrounding the core 20, and two different types of ligands 42 and 44 can bind to the surface of the shell 30. Here, the EML 250 can be formed as a single layer of QDs 10, as shown in Fig. 4A is shown, or can be formed as a multilayer with two or more layers of QDs 10, as shown in Fig. 4B is shown.

[0093] In an exemplary embodiment, the EML 250 can be formed by applying a dispersion comprising the electroluminescent nanoparticles (i.e., QDs 10) in a solvent to the first charge transfer layer 240 by a solution process and volatilization of the solvent.

[0094] As described above, two different types of ligands 42 and 44 can bind to the surface of QD 10. In this exemplary embodiment, the X-type ligands 42, with a negatively charged functional group, are arranged in a portion of the QD 10 surface facing the second electrode 220, which is involved in the injection and transfer of holes; that is, charge carriers of an opposite charge to that of the X-type ligand 42. That is, the X-type ligands 42 are arranged such that they face the interface between the EML 250 and the second charge transfer layer 250. Furthermore, the L-type ligands 44 with a positively charged functional group are arranged in a part of the QD 10 surface facing the first electrode 210, which is involved in the injection and transfer of electrons, i.e. charge carriers of a charge opposite to the charge of the L-type ligand 44.This means that the L-type ligands 44 are arranged such that they face the interface between the EML 250 and the first charge transfer layer 240.

[0095] In this exemplary embodiment, the second charge transfer layer 260 can be a hole transfer layer that provides holes to the EML 250. In an exemplary embodiment, the second charge transfer layer 260 can have a HIL 262 formed adjacent to the second electrode 220 between the second electrode 220 and the EML 250, and an HTL 264 formed adjacent to the EML 250 between the second electrode 220 and the EML 250.

[0096] The HIL 262 can be formed from a material selected from the group consisting of PEDOT:PSS, F4-TCNQ-doped TDATA, for example, a p-doped phthalocyanine (e.g., F4-TCNQ-doped ZnPc), F4-TCNQ-doped α-NPD, HAT-CN, and a combination thereof, but the present disclosure is not limited thereto. As an example, a dopant such as F4-TCNQ can be used to dope a host in an amount of 1 to 30 wt% by weight of the host. The HIL 262 can be omitted according to the structure and type of the LED 200.

[0097] HTL 264 can consist of an inorganic or an organic material. For example, HTL 264 can consist of an organic material selected from the group consisting of arylamines, such as CBP, α-NPD, TPD, Spiro-TPD, DNTPD, TCTA, m-MTDATA, TFB, and poly-TPD; a polyaniline; a polypyrrole; poly(para)phenylenevinylenes, such as PPV, MEH-PPV, and MOMO-PPV, and derivatives thereof; copper phthalocyanine; aromatic tertiary amines or polynuclear tertiary amines; 4,4'-bis(p-carbazolyl)-1,1'-biphenyl compounds; N,N,N',N'-tetraarylbenzidine; PEDOT:PSS and derivatives thereof; poly-N-vinylcarbazole and derivatives thereof; polymethacrylate and derivatives thereof; Poly(9,9-octylfluorene) and derivatives thereof; Poly(spirofluorene) and derivatives thereof; NPB; Spiro-NPB and a combination thereof.

[0098] The HTL 264 can consist of an inorganic material selected from the group consisting of metal oxides such as NiO, MoO3; Cr2O3; Bi2O3; and p-type ZnO; non-oxidized equivalents such as copper thiocyanate (CuSCN), Mo2S and p-type GaN; and a combination thereof.

[0099] The second charge transfer layer 260 can be formed as a single layer. For example, the second charge transfer layer 260 can consist only of the HTL 264 without the HIL 262, or it can be produced by doping the above compound with a hole-transporting organic material and a hole injection material (e.g., PEDOT: PSS). The thicknesses of the HIL 262 and the HTL 264 can be in the range of 10 to 200 nm, and preferably 10 to 100 nm, but the present disclosure is not limited thereto.

[0100] Similar to the first exemplary embodiment, the QLED 200 according to the second exemplary embodiment of the present disclosure can have at least one exciton blocking layer arranged adjacent to the EML 250. For example, the QLED 200 can further have an EBL 250 arranged between the EML and the HTL 264 to control and prevent the transfer of electrons, and an HBL arranged between the ETL 244 and the EML 250 to control and prevent the transfer of holes.

[0101] As described above, according to this exemplary embodiment, different types of ligands bind to the surface of QD 10, which is the electroluminescent nanoparticle forming the EML 250. Within the EML 250, the negatively charged X-type ligands 42 are located in a portion of the QD surface facing the second electrode 220, which is involved in the generation, injection, and transfer of holes carrying a charge opposite to that of the X-type ligands 42. Specifically, the X-type ligands 42 are arranged to face the interface between the EML 250 and the HTL 264 in the second charge transfer layer 260.On the other hand, in the EML 250, the L-type ligands 44, which have a positive charge, are arranged in a part of the QD surface facing the first electrode 210, which is involved in the generation, injection, and transfer of electrons that have a charge opposite to that of the L-type ligand 44. In particular, the L-type ligands 44 are arranged such that they face the interface between the EML 250 and the ETL 244 in the first charge transfer layer 240.

[0102] Holes, i.e., positive charge carriers, and electrons, i.e., negative charge carriers, are rapidly transferred to the surface of the QD 10 used in the EML 250 due to the X-type ligands 42 and the L-type ligands 44, which have opposite charges. Because the holes and electrons in the EML 250 are balanced and quickly recombine, the LED 200 can have improved luminous efficacy and operate at a lower voltage.

[0103] Furthermore, since the L-type ligands 44 bind to the surface of the QD 10 by replacing the X-type ligands 42 without interacting with an organic component, a smaller amount of organic components remains on the QD 10 according to the present disclosure. Accordingly, the QDs 10 can be applied uniformly, and the EML 250 can thus be controlled to have a uniform thickness. If, in addition, the second charge transfer layer 260 and the second electrode 220 are stacked on the EML 250, the organic components do not penetrate the second charge transfer layer 260 and the second electrode 220. Therefore, the boundary between the second charge transfer layer 260 and the second electrode 220 can be clearly distinguished, and the second charge transfer layer 260 and the second electrode 220 can be formed with desired shapes or thicknesses.

[0104] Therefore, the QLED, in which QD 10 is used as an electroluminescent nanoparticle according to the present disclosure, and in which different ligand types 42 and 44 bind to two distinguishable regions of the QD surface in the light-emission layer, can be applied to a light-emitting device, for example, a lighting device or a display device. As an example, a light-emitting QD display device with the QLED is described, in which QD 10, which is the electroluminescent nanoparticle according to the present disclosure, is used in the emission layer. Fig. Figure 5 is a cross-sectional view of a QD light-emitting device according to an exemplary embodiment of the present disclosure.

[0105] As in Fig. As shown in Figure 5, the QD light-emitting display device 300 comprises a substrate 310, a driver thin-film transistor Tr which is a driver element arranged on the substrate 310, and a QLED 400 which is connected to the driver thin-film transistor Tr.

[0106] A semiconductor layer 322, consisting of an oxide semiconductor material or polycrystalline silicon, is formed on the substrate 310. If the semiconductor layer 322 is made of an oxide semiconductor material, a light-shielding pattern (not shown) can be formed beneath the semiconductor layer 322 to prevent light from entering the semiconductor layer 322, thus preventing light-induced degradation of the semiconductor layer 322. In contrast, the semiconductor layer 322 can be made of polycrystalline silicon, and in this case, opposite edges of the semiconductor layer 322 can be doped with impurities.

[0107] A gate insulating film 324, consisting of an insulating material, is formed on the semiconductor layer 322. The gate insulating film 324 can be made of an inorganic insulating material such as silicon dioxide (SiO2) or silicon nitride (SiN). x ). A gate electrode 330, made of a conductive material, such as a metal, is formed on the gate insulating film 324 to correspond to the center of the semiconductor layer 322.

[0108] An intermediate insulating film 332, consisting of an insulating material, is formed on the gate electrode 330. The intermediate insulating film 332 can be made of an inorganic insulating material such as silicon dioxide (SiO2) or silicon nitride (SiN). x ) or be formed from an organic insulating material such as benzocyclobutene or photoacrylic.

[0109] The interlayer insulating film 332 has first and second semiconductor layer contact holes 334 and 336, which expose two opposite sides of the semiconductor layer 322. The first and second semiconductor layer contact holes 334 and 336 are arranged on both sides of the gate electrode 330 such that they are spaced apart from the gate electrode 330. A source electrode 340 and a drain electrode 342, made of a conductive material such as a metal, are formed on the interlayer insulating film 332.

[0110] The source electrode 340 and the drain electrode 342 are arranged on both sides of the gate electrode 330 such that they are spaced apart from the gate electrode 330 and are connected to two opposite sides of the semiconductor layer 322 via the first and second semiconductor layer contact holes 334 and 336.

[0111] The semiconductor layer 322, the gate electrode 330, the source electrode 340 and the drain electrode 342 together form the driver thin-film transistor Tr, which is a driver element.

[0112] In Fig. 5. The driver thin-film transistor Tr has a coplanar structure in which the gate electrode 330, the source electrode 340, and the drain electrode 342 are arranged on the semiconductor layer 322. Alternatively, the driver thin-film transistor Tr can have an inverted stepped structure in which a gate electrode is arranged below the semiconductor layer and a source electrode and a drain electrode are arranged on the semiconductor layer. In this case, the semiconductor layer can be made of amorphous silicon.

[0113] Although not in Fig. As shown in Figure 5, pixel areas are defined by intersecting gate and data lines, and a switching element connected to the gate and data lines is provided. This switching element is connected to the driver thin-film transistor Tr, which is a driver element. Additionally, a current line, spaced apart and parallel to the gate or data line, and a storage capacitor can be provided to maintain a constant voltage across the gate electrode of the driver thin-film transistor Tr during a frame.

[0114] Meanwhile, a passivation layer 350 has a drain contact hole 352 through which the drain electrode 342 of the driver thin-film transistor Tr is exposed, so that it covers the driver thin-film transistor Tr.

[0115] A first electrode 410, connected to the drain electrode 342 of the driver thin-film transistor Tr through the drain contact hole 352, is formed on the passivation layer 350 for each pixel area. The first electrode 410 can be an anode or a cathode and can be made of a conductive material with a relatively high work function. For example, the first electrode 410 can be made of a doped or undoped metal oxide, such as ITO, IZO, ITZO, ICO, SnO₂, In₂O₃, Cd:ZnO, F:SnO₂, In:SnO₂, Ga:SnO₂, or AZO, or, other than the metal oxide mentioned above, it can be made of a metal material containing nickel (Ni), platinum (Pt), gold (Au), silver (Ag), iridium (Ir), or a CNT.

[0116] If the light-emitting QD indicator device 300 of the present disclosure is of a top-emission type, a reflective electrode or a reflective layer may be provided below the first electrode 410. The reflective electrode or the reflective layer may, for example, consist of an aluminum-palladium-copper (APC) alloy.

[0117] Furthermore, a bench layer 368 is formed on the passivation layer 350 to cover an edge of the first electrode 410. The bench layer 368 is configured such that the center of the first electrode 410, corresponding to a pixel area, is exposed.

[0118] An emission layer 430 with the QDs 10, which are electroluminescent nanoparticles according to the present disclosure, is formed on the first electrode 410. The emission layer 430 can consist of only one EML or have several charge transfer layers to increase the light yield. As an example, the first charge transfer layer can be 140 or 240 (see Fig. 3 and Fig. 4) furthermore, the second charge transfer layer 160 or 260 (see) is formed between the first electrode 410 and the emission layer 430. Fig. 3 and Fig. 4) can also be formed between the emission layer 430 and a second electrode 420.

[0119] The QD 10 in the emission layer 430 can consist of a core 20, which is a phosphor, and a shell 30 surrounding the core 20, and various ligand types 42 and 44 bind to the surface of the shell 30. Fig. Figure 5 illustrates that the X-type ligands 42 are arranged near the first electrode 410 and the L-type ligands 44 are arranged near the second electrode 420. Alternatively, the X-type ligands 42 can be arranged near the second electrode 420 and the L-type ligands 44 can be arranged near the first electrode 410.

[0120] The second electrode 420 is formed on the emission layer 430, which is formed on the substrate 310. The second electrode 420 can be arranged over the entire surface of a display area, can be made of a conductive material with a relatively low work function, and can be a cathode or anode. For example, the second electrode 420 can be Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF₂ / Al, CsF / Al, CaCO₃ / Al, BaF₂ / Ca / Al, Al, Mg, Au:Mg, or Ag:Mg.

[0121] As described above, on the QD 10, which is an electroluminescent nanoparticle, the X-type ligands 42 with a negatively charged functional group and the L-type ligands 44 with a positively charged functional group are arranged such that each faces an electrode involved in the generation, injection, and transfer of a charge opposite to that of the corresponding ligand. Due to the X-type ligands 42 and 44 having opposite charges with respect to the holes and electrons, respectively, the holes and electrons can be transferred rapidly and in a balanced manner to the emission layer 430. Therefore, the QLED 400 and the QD light-emitting display device 300, which incorporates these features, can have improved luminous efficacy, and the QLED 400 can be operated at a lower voltage.

[0122] Furthermore, since a small amount of organic components remains on the QDs 10 binding the L-type ligands 44, the QDs 10 can be applied uniformly to form the emission layer 430, and thus the emission layer 430 can be adjusted to have a uniform thickness. Since the remaining organic components do not penetrate the emission layer 430 and the second electrode 420, the boundary between the emission layer 430 and the second electrode 420 can also be clearly distinguished, and the emission layer 430 and the second electrode 420 can be formed with desired shapes or thicknesses.

[0123] The present disclosure is described below by means of the following examples, but the present disclosure is not limited to the technical ideas described in the following examples. SYNTHESIS EXAMPLE 1 SYNTHESIS OF SINGLE LAYERS OF QDs WITH X-TYPE LIGANDS AND L-TYPE LIGANDS1) Synthesis of ZnSe / ZnS core / shell QDs

[0124] 0.073 g of zinc acetate, 0.237 g of oleic acid, and 0.032 g of selenium were added to 26 mL of octadecene (ODE) as solvent in a three-necked flask. The resulting mixture was heated under vacuum at 120 °C for 120 minutes to remove moisture, oxygen, and impurities. After switching to a nitrogen atmosphere, the resulting mixture was heated at 300 °C for 1 hour, forming a ZnSe core. The core was cooled to room temperature, and 7 mL of 0.4 M zinc oleate and 1 mL of 1 M tributylphosphine sulfide (TBPS) were added to the flask in which the core had been formed to create a ZnS shell to which the oleate, i.e., the X-type ligand, was bound. The resulting mixture was heated at 280 °C for 1 hour, forming a ZnS shell.For work-up, a process of adding an excess amount of acetone and carrying out precipitation by centrifugation was repeated several times, and thus ZnSe / ZnS-QDs were synthesized, to which the X-type ligands (i.e., oleate) were finally bound. 2) Synthesis of dual-ligand-binding QDs by TAEA treatment

[0125] The precipitated QDs (ZnSe / ZnS) as described above were dispersed in hexane or toluene. The dispersion, containing the QDs at a concentration of 10 mg / ml, was centrifugally coated (2000 rpm, 60 seconds) onto a substrate and dried for 30 minutes at 70 °C. 1 to 2 ml of Tris(2-aminoethyl)amine (TAEA) was dropwise applied to the QD-coated surface, followed by centrifugal coating (500 rpm, 30 seconds). The resulting substrate was dried at 60 to 80 °C for 120 minutes to induce ligand exchange in a portion of the QD surface (an area not in contact with the substrate) by diffusion according to the difference in ligand concentration and the interaction between Zn and an amino group. The work-up was carried out once, with the resulting product being resuspended in an organic solvent such as hexane or toluene. SYNTHESIS EXAMPLE 2 SYNTHESIS OF DOUBLE LAYERS OF QDs WITH X-TYPE LIGANDS AND L-TYPE LIGANDS

[0126] The procedures described in Synthesis Example 1 were repeated, except that the concentration of the applied ZnSe / ZnS core / shell QDs and the TAEA content were approximately doubled to arrange and apply the QDs as a bilayer on a substrate. COMPARATIVE SYNTHESIS EXAMPLE: SYNTHESIS OF A SINGLE LAYER OF QDs CONSISTING ONLY OF X-TYPE LIGANDS

[0127] In contrast to Synthesis Example 1, QDs in which only X-type ligands (i.e., oleate) were bound to the QD surface were synthesized without performing a TAEA treatment. EXAMPLE 1 MEASUREMENT OF THE PHYSICAL PROPERTIES OF QDs

[0128] The physical properties of the QDs synthesized in Synthesis Example 1 were measured. To measure the particle size of the QDs, one or two droplets of the QDs dispersed in hexane according to Synthesis Example 1 were placed on a TEM grid, dried, and analyzed using TEM (Helios Nanolab 600i, FEI). Fig. Figure 6 shows a TEM image of the QDs synthesized in Synthesis Example 1. The average particle size of the QDs was 7.5 nm. Furthermore, the QDs dispersed in hexane according to Synthesis Example 1 were dissolved in sulfuric or hydrochloric acid and subjected to inductively coupled plasma mass spectrometry (ICP-MS; ELAN DRC®, Perkin-Elmer). The analysis results show that the synthesized QDs had a Zn content of 52.8 wt%, a Se content of 21.2 wt%, and a S content of 26.0 wt%, indicating that the QDs were synthesized with a desired core / shell structure. Furthermore, FT-IR (FTS7000e, VARIAN) was performed by applying the dispersion containing the QDs in hexane (obtained by Synthesis Example 1) to KBr or using powder-type QDs. The FT-IR result shows the binding of TAEA ligands, which were not present on the QDs synthesized in the comparison example (see Fig. 7).

[0129] Meanwhile, a powder produced by drying the QDs synthesized in the comparison example was subjected to thermogravimetric analysis (TGA; Pyris1, Perkin-Elmer). The TGA results confirmed that a considerable amount, i.e., 40 wt%, of the organic material remained (see Fig. 8A). On the other hand, according to the TGA for the QDs synthesized in Synthesis Example 1, the content of the remaining organic material was no more than 20 wt% (see Fig. 8B), which indicates that the content of the remaining organic material in the case of the QDs, where the different ligand types were bound to the QD surface, was reduced to less than half.

[0130] To confirm whether different ligand types were bound to different regions of the QD surface, a TOF-SIMS analysis was subsequently performed. One hour after a silicon wafer had been treated with UV ozone, a sample was prepared by centrifugal coating (2,000 rpm, 60 seconds) of the dispersion containing the QDs obtained in Synthesis Example 1 onto the wafer. The sample was then analyzed at predetermined time intervals, starting from the farthest part of the wafer and ending at the nearest part. Fig. Figure 9 shows a result of a TOF-SIMS analysis for the QDs synthesized in Synthesis Example 1. As in Fig. As shown in Figure 9, the QD surface furthest from the wafer and not covered by it mainly contained carbon-nitrogen bonds in the TAEA ligands, i.e., the L-type ligands, and almost no -O bonds, which are contained in the X-type ligands. However, with decreasing distance from the wafer, the content of L-type ligands decreased and the content of X-type ligands increased, confirming that the previously bonded X-type ligands are mainly bound to the QD surface covered by the wafer.

[0131] As a result of the measurement of the photoluminescence (PL) intensity and quantum yield (QY) for the QDs synthesized in synthesis example 1, it was also confirmed that the PL intensity and quantum yield were similar to those of the QDs synthesized in the comparison synthesis example (the result was not shown), which suggests that there was no difference in the optical properties. EXAMPLE 2: QLED MANUFACTURING

[0132] An LED was fabricated using a single layer of QDs synthesized according to Synthesis Example 1. ITO (anode, 50 nm) was treated with UV ozone for 1 hour, and then emission layers and a cathode were stacked in the following order: a HIL (PEDOT:PSS, spin coating (2000 rpm) followed by drying at 120 °C for 30 minutes; 25 nm), an HTL (HTL, TFB, spin coating (2000 rpm) followed by drying at 120 °C for 30 minutes; 24 nm), an EML (EML, QDs from Synthesis Example 1), spin coating (2000 rpm) followed by drying at 70 °C for 60 minutes (18 nm), and an ETL (TPBi, deposition (3×10 –6 Torr = 0.4 mPa , 0.1 Å / s); 52 nm) and a cathode (Al, 3×10 –6 Torr = 0.4 mPa, 4 to 5 Å / s); 80 nm). EXAMPLE 3: QLED MANUFACTURING

[0133] A QLED was produced by repeating the procedures of Example 2, except that a bilayer of QDs according to Synthesis Example 2 was used as an EML. COMPARISON EXAMPLE OF QLED PRODUCTION

[0134] A QLED was prepared by repeating the procedures of Example 2, except that the QDs were used for an EML according to the comparison synthesis example, in which QDs binding only the X-type ligands to their surface. EXAMPLE 4 EVALUATION OF PHYSICAL PROPERTIES OF THE QLED1) Evaluation of the luminescence properties

[0135] A driver voltage (V), a driver current (A), a current density (mA / cm³) 2 ), a current efficiency (Cd / A), a power efficiency (lm / W_, external quantum efficiency (EQE)) and the luminance (Cd / m²) 2The luminous efficacy of each of the LEDs produced in Example 1 and the comparison example was measured. One measurement result is shown in Table 1. Table 1 Luminescence properties of QLEDs V A mA / cm 2 Cd / A lm / W EQE(%) Cd / m 2 Beispiel 1 5,525 0,0009 10 1,682 0,956 2,278 168,2 Vergleichsbeispiel 3,986 0,009 10 0, 1012 0,079 0,146 10,12

[0136] As shown in Table 1, when QDs in which the X-type and L-type ligands were bound to specific regions of the QD surface were applied to an EML, compared to QDs in which only X-type ligands were bound to the QD surface, the driver voltage decreased by 38.6% and the current decreased by a factor of 10. At the same current density, the current efficiency increased by a factor of 16.6, the power efficiency increased by a factor of 12.1, the external quantum yield increased by a factor of 15.6, and the luminance increased by a factor of 16.6.Therefore, it was confirmed that if the QDs according to the present disclosure, in which different ligand types were bound to specific areas of the QD surface, were applied to the EML, the QLED, which can be operated at low voltage and has greatly improved luminous efficacy, can be realized and applied to a light-emitting QD device. 2) Evaluation of the morphology of QLED-forming layers

[0137] The morphology of the layers in each of the LEDs produced in Examples 2 and 3 and in the comparison example was evaluated using TEM. Fig. 10A and Fig. Figure 10B are electron microscope images that schematically represent the cross-sectional structures of EMLs consisting of a single layer ( Fig. 10A) and a double layer ( Fig. 10B) of QDs synthesized according to an exemplary embodiment of the present disclosure, wherein ligands with different properties were applied to the QD surface. It was confirmed that, since the two types of ligands with different charge properties were bound to specific regions of the QD surface, the QDs can be bound as a single layer or a double layer, thereby making it easy to adjust or control the thickness of the EML.

[0138] Meanwhile, the Fig. 11A and Fig. 11B Electron microscope images schematically showing the cross-sectional structure of an LED with an EML by applying QDs synthesized according to an exemplary embodiment of the present disclosure, in which ligands with different properties are bound to the QD surface. As shown in the image on the left side of each of the Fig. 11A and Fig. As shown in Figure 11B, when the EML was formed using QDs where only X-type ligands were bound to the QD surface, the thickness of the EML was not uniform, and the ETL and a second electrode were not stacked with the desired shapes. In contrast, as shown in the image on the right of each of the Fig. 11A and Fig. As shown in Figure 11B, if the QDs according to the present disclosure, in which both the X-type ligands and the L-type ligands are bound to specific areas of the QD surface, are used in the EML, the thickness of the EML can be uniformly adjusted and the ETL and the second electrode can be easily formed with the desired shapes.

[0139] According to the present disclosure, QDs in which X-type ligands are bonded to a first region of the surface of a QD particle, and L-type ligands are bonded to a second region of the QD surface, which is an opposite part of the first region, are applied in an EML.

[0140] Since QDs are used in which two different ligand types bind to specific areas of the QD surface, a balanced transfer of charges to the EML can be achieved, and thus a QLED and a light-emitting device that can be operated at a lower driver voltage and have improved luminous efficacy can be manufactured and realized.

[0141] Additionally, organic components remaining on the QD surface can be reduced by a ligand exchange reaction. Therefore, an EML into which the QDs are introduced according to the present disclosure can be effectively adjusted to a desired thickness, and the EML, a charge transfer layer, and an adjacent electrode can be easily formed.

[0142] Therefore, when using QDs where two different ligand types are introduced into the QD surface, a QLED with improved luminous efficacy and low driver voltage, an EML that can be easily adjusted to a desired thickness, a charge transfer layer and electrode with suitable shapes, and a QD light-emitting device that uses these can be produced.

Claims

[1] Light-emitting diode (100, 200) with several quantum dots (10), having the light-emitting diode (100, 200): a first electrode (110, 210) and a second electrode (120, 220); an emitting material layer (150, 250); an electron transfer layer (164, 244); and a hole transfer layer (144, 264), wherein the emitting material layer (150, 250) is arranged between the electron transfer layer (164, 244) and the hole transfer layer (144, 264) and the emitting material layer (150, 250) has the quantum dots (10), where the quantum dots exhibit (10): a semiconductor nanocrystal or metal oxide core (20); a shell (30) covering the semiconductor nanocrystal or metal oxide core (20), wherein the shell (30) has an outer surface; an X-type ligand (42) having a functional group selected from the group consisting of a carboxylate group, a phosphate group and a thiolate group, which is bonded to a first region of the outer surface; and an L-type ligand (44) having a functional group selected from the group consisting of an amino group, a thiol group, a phosphine group and a phosphine oxide group, which is bonded to a second region of the outer surface, wherein the X-type ligand (42) is bound to the first region of the outer surface by a negatively charged functional group, and the L-type ligand (44) is bound to the second region of the outer surface by an undivided electron pair, wherein a multitude of the first regions of the outer surfaces of the quantum dots (10) are proximal to the hole transfer layer (144, 264) and distal to the electron transfer layer (164, 244), wherein a multitude of the second regions of the outer surfaces of the quantum dots (10) are proximal to the electron transfer layer (164, 244) and distal to the hole transfer layer (144, 264), and where the outer surface is spherical and the first area is a first hemisphere and the second area is a second hemisphere. [2] Light-emitting diode (100, 200) according to claim 1, wherein the X-type ligand (42) further comprises a saturated or unsaturated C5-C30 hydrocarbon chain. [3] Light-emitting diode (100, 200) according to claim 1 or 2, wherein the X-type ligand (42) has one of the following structures: wherein: n is an integer in the range of 6 to 16; m is an integer in the range of 4 to 9; p is an integer in the range of 4 to 9; and X is a carboxylate group, a phosphate group, or a thiolate group. [4] Light-emitting diode (100, 200) according to claim 3, wherein the X-type ligand (42) is selected from the group consisting of octanoic acid, decanoic acid, dodecanoic acid, myristic acid, palmitic acid, hexadecanoic acid, stearic acid, oleic acid and combinations thereof. [5] Light-emitting diode (100, 200) according to one of claims 1 to 4, wherein the L-type ligand (44) is selected from the group consisting of linear or branched C1 to C10 alkylamines, alicyclic C4 to C8 amines and aromatic C5 to C20 amines, linear or branched C1 to C10 alkylphosphines, linear or branched C1 to C 10 -Alkylphosphine oxides and a combination thereof. [6] Light-emitting diode (100, 200) according to any one of claims 1 to 4, wherein the L-type ligand (44) is tris(2-aminoethyl)amine, tris(2-aminomethyl)amine and N-butyl-N-ethylethane-1,2-diamine, ethylenediamine, pentaethylenehexamine, cyclohexane-1,2-diamine, cyclohexene-1,2-diamine or 2,3-diaminopyridine. [7] Light-emitting device (300) comprising a light-emitting diode (100, 200) according to any one of claims 1 to 6. [8] Light-emitting device (300) according to claim 7, further comprising a substrate (310), wherein the light-emitting diode (100, 200) is located on the substrate (50); and a driver element (Tr) that is arranged between the substrate (310) and the light-emitting diode (100, 200) and is coupled to the light-emitting diode (100, 200).

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