Composite material, quantum dot light-emitting diode and preparation method thereof

Abstract

The present invention discloses a composite material, a quantum dot light-emitting diode and a preparation method thereof. The composite material includes metal oxide nanoparticles and an MN₄-type half-metal. The metal oxide nanoparticles are combined with the MN₄-type half-metal, wherein M in the MN₄-type half-metal is a metal atom with an outermost 3d electron orbital. After the MN₄-type half-metal is compounded with the metal oxide nanoparticles in the present invention, by virtue of the characteristic that the surface metal atoms in the half-metal are easily coordinated with the hydroxyl ligands on the surface of the metal oxide nanoparticles, the metal oxide nanoparticles can be uniformly dispersed. The MN₄-type half-metal has a high conductivity, and by being compounded with the metal oxide nanoparticles, its conductivity can be improved. The MN₄-type half-metal has a small band gap, making it easier for the electrons of the composite material formed by combining it with the metal oxide nanoparticles to be excited from the valence band to the conduction band, increasing the carrier concentration, facilitating carrier transport, and improving the light-emitting efficiency of the device.

Description

Technical Field

[0001] The present invention relates to the field of quantum dot light-emitting diodes, and particularly to composite materials, quantum dot light-emitting diodes and their preparation methods. Background Art

[0002] Semiconductor quantum dots (QDs) have quantum size effects. By regulating the size of quantum dots, light emission with specific wavelengths can be achieved. The emission wavelength tuning range of CdSe QDs can cover from blue light to red light. In traditional inorganic electroluminescent devices, electrons and holes are injected from the cathode and anode respectively, and then recombine in the light-emitting layer to form excitons for light emission.

[0003] In recent years, inorganic semiconductors as electron transport layers or hole transport layers have become a hot research topic. Nano-ZnO, TiO2, and SnO2 are wide-bandgap semiconductor materials, which have attracted the attention of many researchers due to their quantum confinement effects, size effects, and excellent fluorescence properties, and are often used as electron transport layers. In addition, transition metal oxides (WO3, MoO3, NiO, Cu2O, ReO3, and V2O5) are used as hole transport layers in many quantum dot light-emitting diodes (QLEDs) and have achieved good performance. However, when inorganic metal oxide semiconductor materials are used as electron transport layers or hole transport layers in QLEDs, their carrier transport efficiency is still relatively low during application, resulting in low device efficiency.

[0004] Therefore, the existing technology still needs to be improved and developed. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the purpose of the present invention is to provide a composite material, a quantum dot light-emitting diode and its preparation method, aiming to solve the problem that the carrier transport efficiency of existing inorganic metal oxides as charge transport materials is still relatively low.

[0006] The technical solution of the present invention is as follows:

[0007] In the first aspect of the present invention, a composite material is provided, which includes metal oxide nanoparticles and MN4-type half-metals. The metal oxide nanoparticles and MN4-type half-metals are combined, where M in the MN4-type half-metal is a metal atom with a 3d electron orbital in the outermost layer.

[0008] Optionally, the surface of the metal oxide nanoparticles is combined with hydroxyl ligands, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are coordinately bonded to the metal elements on the surface of the MN4-type half-metal.

[0009] Optionally, the MN4-type half-metal is selected from one or more of FeN4-type half-metals, CoN4-type half-metals, MnN4-type half-metals, and AlN4-type half-metals.

[0010] Optionally, the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material; or, the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material.

[0011] Optionally, the metal oxide nanoparticles used as an electron transport material are selected from one or more of ZnO nanoparticles, TiO2 nanoparticles, SnO nanoparticles, and SnO2 nanoparticles;

[0012] Or, the metal oxide nanoparticles used as a hole transport material are selected from one or more of WO3 nanoparticles, MoO3 nanoparticles, NiO nanoparticles, Cu2O nanoparticles, ReO3 nanoparticles, and V2O5 nanoparticles.

[0013] Optionally, the molar ratio of the metal oxide nanoparticles to the MN4-type half-metal is 1:(0.2 - 0.5).

[0014] In a second aspect of the present invention, there is provided a method for preparing the composite material described in the present invention, which includes the steps of:

[0015] Providing metal oxide nanoparticles and an MN4-type half-metal, where M in the MN4-type half-metal is a metal atom with an outermost 3d electron orbital;

[0016] Mixing the metal oxide nanoparticles and the MN4-type half-metal in an organic solvent and reacting under stirring to obtain a composite material in which the metal oxide nanoparticles and the MN4-type half-metal are combined.

[0017] Optionally, the reaction temperature is 60 - 80 °C, and / or the reaction time is 2 - 4 h.

[0018] In a third aspect of the present invention, there is provided a quantum dot light-emitting diode, which includes a hole transport layer, and the hole transport layer includes the composite material described in the present invention;

[0019] Or, it includes an electron transport layer, and the electron transport layer includes the composite material described in the present invention.

[0020] In a fourth aspect of the present invention, there is provided a method for preparing a quantum dot light-emitting diode, which includes the steps of:

[0021] Preparing a hole transport layer, and the material of the hole transport layer includes the composite material described in the present invention;

[0022] Or, preparing an electron transport layer, and the material of the electron transport layer includes the composite material described in the present invention.

[0023] Beneficial effects: In the present invention, due to the small particle size of metal oxide nanoparticles, they are prone to agglomeration. After the MN4-type half-metal is compounded with metal oxide nanoparticles, by utilizing the property that the surface metal atoms in the half-metal are easily coordinated with the hydroxyl ligands on the surface of the metal oxide nanoparticles, the metal oxide nanoparticles can be uniformly dispersed, effectively avoiding the agglomeration between the metal oxide nanoparticles. In addition, the MN4-type half-metal has a high electrical conductivity. By compounding with metal oxide nanoparticles, the electrical conductivity of the metal oxide nanoparticles can be improved. Furthermore, the band gap of the MN4-type half-metal is small, making it easier for the electrons of the composite material formed by the compounding of the MN4-type half-metal and the metal oxide nanoparticles to be excited from the valence band to the conduction band, increasing the carrier concentration, which is beneficial to the transport of carriers and improving the QLED luminescence efficiency. Description of the Drawings

[0024] Figure 1 is the chemical structural formula of the FeN4-type half-metal.

[0025] Figure 2 is a schematic flow chart of a preparation method of a composite material provided by an embodiment of the present invention.

[0026] Figure 3 is a schematic structural diagram of a quantum dot light-emitting diode provided by an embodiment of the present invention.

[0027] Figure 4 is a schematic flow chart of a preparation method of a quantum dot light-emitting diode provided by an embodiment of the present invention. Detailed Embodiments

[0028] The present invention provides a composite material, a quantum dot light-emitting diode and a preparation method thereof. To make the purpose, technical solution and effects of the present invention clearer and more definite, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0029] The inventors unexpectedly found that due to the characteristics of the half-metal material that one spin direction has a metal conductive behavior and the other spin direction has a semiconductor conductive behavior, it has broad application prospects in electronic devices. In the traditional half-metal energy band structure, the conduction band and the valence band have a small overlap (very small negative energy gap) or just tangent (zero energy gap), resulting in the macroscopic carrier transport performance of this half-metal being weaker than that of typical metals and stronger than that of typical semiconductors. Further research found that compounding the half-metal material with metal oxide nanoparticles as the electron (hole) transport layer can improve the carrier transport efficiency of the metal oxide nanoparticles.

[0030] Based on this, an embodiment of the present invention provides a composite material, which includes metal oxide nanoparticles and MN4-type half metals. The metal oxide nanoparticles are combined with the MN4-type half metals, wherein M in the MN4-type half metals is a metal atom with an outermost 3d electron orbital.

[0031] In one embodiment, the composite material is composed of metal oxide nanoparticles and MN4-type half metals.

[0032] In one embodiment, hydroxyl ligands are bonded to the surface of the metal oxide nanoparticles, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are coordinately bonded to the metal elements on the surface of the MN4-type half metals.

[0033] In this embodiment, the MN4-type half metal material is a type of material with a diamond-like structure constructed based on MN4 tetrahedrons with M atoms as the center and N atoms occupying the vertex positions and N=N bonds as the building blocks (M in the MN4 tetrahedron is a metal atom with an outermost 3d electron orbital). Taking the FeN4-type half metal as an example, a diamond-like structure of the FeN4-type half metal is constructed through FeN4 tetrahedrons with Fe atoms as the center and N=N bonds as the building blocks, as shown in Figure 1 shown. The π* bond (π antibond) in the N=N double bond provides a high concentration of delocalized electrons, which plays a decisive role in the conductivity of this material, and its conductivity is as high as 5.07×10 5 S / cm. On the one hand, the N=N bond provides a bridge for carrier transport. On the other hand, the tetrahedron formed by N atoms and M metal atoms causes the 3d electron orbitals to split under the action of the crystal field. The two are further hybridized to form bonds, so that the energy states in a certain spin direction are split into bonding states and antibonding states, thereby opening the band gap, making the band gap of such MN4-type half metals greater than 2 eV, and thus can be used in the application of semiconductor electronics devices.

[0034] In addition, due to the small particle size of the metal oxide nanoparticles, they are prone to agglomeration. After the MN4-type half metals are compounded with the metal oxide nanoparticles in this embodiment, by utilizing the characteristic that the surface metal atoms in the half metals are easily coordinated with the hydroxyl ligands on the surface of the metal oxide nanoparticles, the metal oxide nanoparticles can be evenly dispersed, effectively avoiding the agglomeration between the metal oxide nanoparticles. In addition, the MN4-type half metals have a high conductivity. By compounding with the metal oxide nanoparticles, the conductivity of the metal oxide nanoparticles can be improved. And, the band gap of the MN4-type half metals is small, making it easier for the electrons of the composite material formed by the compounding of the MN4-type half metals and the metal oxide nanoparticles to be excited from the valence band to the conduction band, increasing the carrier concentration, being conducive to the transport of carriers, and improving the QLED luminescence efficiency.

[0035] In one embodiment, the MN4 type half-metal can be selected from one or more of FeN4 type half-metal, CoN4 type half-metal, MnN4 type half-metal, AlN4 type half-metal, etc., but not limited thereto.

[0036] In one embodiment, the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material; or, the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material.

[0037] In one embodiment, the metal oxide nanoparticles used as an electron transport material can be selected from one or more of ZnO nanoparticles, TiO2 nanoparticles, SnO nanoparticles, SnO2 nanoparticles, etc., but not limited thereto.

[0038] In one embodiment, the metal oxide nanoparticles used as a hole transport material can be selected from one or more of WO3 nanoparticles, MoO3 nanoparticles, NiO nanoparticles, Cu2O nanoparticles, ReO3 nanoparticles, and V2O5 nanoparticles, etc., but not limited thereto.

[0039] In one embodiment, the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is 1:(0.2 - 0.5). Because when the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is less than 1:0.2, the amount of the MN4 type half-metal combined with the metal oxide nanoparticles is small, and the effect on improving the carrier transport performance of the metal oxide nanoparticles is not obvious. When the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is greater than 1:0.5, the proportion of the MN4 type half-metal component is large, while the proportion of the metal oxide nanoparticle component is small, and the carrier transport performance decreases.

[0040] The embodiment of the present invention provides a preparation method of a composite material, as Figure 2 shown, including steps:

[0041] S10. Provide metal oxide nanoparticles and an MN4 type half-metal, wherein M in the MN4 type half-metal is a metal atom with an outermost 3d electron orbital;

[0042] S11. Mix the metal oxide nanoparticles and the MN4 type half-metal in an organic solvent and react under stirring to obtain a composite material in which the metal oxide nanoparticles and the MN4 type half-metal are combined.

[0043] In step S10, in one embodiment, the preparation method of the metal oxide nanoparticles includes steps: Dissolve a metal salt in a first organic solvent and stir, add an alkali solution, continue to stir, precipitate with a precipitating agent after cooling, wash, and dry to obtain the metal oxide nanoparticles.

[0044] In this embodiment, a metal salt reacts with an alkali solution to form a hydroxide (M(OH) x ), and M(OH) x undergoes a polycondensation reaction to dehydrate and form MO x , where M represents a metal.

[0045] In one embodiment, the molar ratio of OH - in the alkali solution to the metal ions in the metal salt is (1.8 - 4.5):1, and the pH of the alkali solution is 12 - 13. The dosage of the alkali solution is specifically adjusted according to the valence state of the metal ions. For example, when the metal ions are +2 valence (Zn 2+ , Ni 2+ ), the molar ratio of the alkali solution to the metal ions is 2:1. Therefore, by maintaining the molar ratio of the alkali solution to the metal ions at (1.8 - 2.5):1, metal oxide nanoparticles can be formed. When the metal ions are +4 valence (Ti 4+ , Sn 4+ , Zr 4+ ), the molar ratio of the alkali solution to the metal ions is 4:1. Therefore, by maintaining the molar ratio of the alkali solution to the metal ions at (3.5 - 4.5):1, metal oxide nanoparticles can be formed. When the molar ratio of the alkali solution to the metal ions is less than 1.8:1 or 3.5:1, and the pH < 12, the alkali solution is insufficient and the metal salt is in excess, resulting in an insufficient reaction. When it is greater than 2.5:1 or 4.5:1, and the pH > 13, too high a pH value will cause the hydrolysis and polycondensation rates of the sol in the system to slow down. Therefore, by maintaining the molar ratio of the alkali solution to the metal ions at (1.8 - 4.5):1, it is possible to ensure a sufficient reaction to obtain metal oxide nanoparticles.

[0046] In one embodiment, the concentration of the metal salt solution is 0.2 - 1 M. Herein, the metal salt solution refers to a solution formed by dissolving a metal salt in an organic solvent.

[0047] In one embodiment, after adding the alkali solution, stirring is carried out at a temperature of 60 - 80 °C.

[0048] In one embodiment, after adding the alkali solution, the stirring time is 2 h - 4 h.

[0049] In one embodiment, the metal salt can be one or more of titanium salts, zinc salts, tin salts, zirconium salts, nickel salts, tungsten salts, etc., but is not limited thereto. Specifically, it refers to the precursor salts corresponding to metal oxides that can be used as electron transport layer materials or hole transport layer materials.

[0050] In one embodiment, the zinc salt can be a soluble inorganic zinc salt or an organic zinc salt, such as one or more of zinc acetate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate dihydrate, etc., but is not limited thereto.

[0051] In one embodiment, the titanium salt can be one or more of titanium nitrate, titanium chloride, titanium sulfate, titanium bromide, etc., but is not limited thereto.

[0052] In one embodiment, the tin salt can be a soluble inorganic tin salt or an organotin salt, such as one or more of tin nitrate, tin chloride, tin sulfate, tin methanesulfonate, tin ethanesulfonate, tin propanesulfonate, etc., but is not limited thereto.

[0053] In one embodiment, the nickel salt can be a soluble inorganic nickel salt or an organonickel salt, such as one or more of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate tetrahydrate, etc., but is not limited thereto.

[0054] In one embodiment, the first organic solvent can be one or more of isopropanol, ethanol, propanol, butanol, methanol, etc., but is not limited thereto.

[0055] In this embodiment, the alkali solution is prepared by dissolving an alkali in the first organic solvent. In one embodiment, the alkali can be one or more of ammonia water, potassium hydroxide, sodium hydroxide, lithium hydroxide, ethanolamine, ethylene glycol, diethanolamine, triethanolamine, ethylenediamine, etc., but is not limited thereto.

[0056] In one embodiment, the precipitant is a weakly polar or nonpolar solvent, such as ethyl acetate, heptane, octane, etc., and is not limited thereto.

[0057] In step S10, in one embodiment, the preparation method of the MN4 type half-metal includes the steps of: dissolving a metal salt and a nitrogen source in a second organic solvent, stirring, and then transferring to a high-pressure and high-temperature reaction kettle; first applying high pressure to the reaction kettle, heating after the pressure rises to a predetermined pressure, maintaining the pressure and temperature at a predetermined temperature for a predetermined time after the temperature rises to the predetermined temperature, and finally cooling at the predetermined pressure, and performing pressure relief after cooling to room temperature to obtain the MN4 type half-metal.

[0058] For the specific details of the MN4 type half-metal, see the above, and will not be elaborated here.

[0059] In one embodiment, the nitrogen source can be selected from one or more of urea, ammonium sulfate, ammonium nitrate, ammonium chloride, etc., but is not limited thereto.

[0060] In one embodiment, the second organic solvent can be selected from one or more of aprotic polar solvents such as tetrahydrofuran (THF), dimethylformamide (DMF), dimethyl sulfoxide (DMSO), etc., but is not limited thereto.

[0061] In one embodiment, on a molar ratio basis, the molar ratio of the metal salt to the nitrogen source is 1:(5 - 7). Because when the molar ratio of the metal salt to the nitrogen source is less than 1:5, the nitrogen source is insufficient and the metal salt is in excess, and the reaction to generate MN4 is not sufficient; when the molar ratio of the metal salt to the nitrogen source is greater than 1:7, the nitrogen source is in excess, and impurity compounds are easily formed and not easily removed. When the molar amount ratio of the metal salt to the nitrogen source is 1:(5 - 7), it can ensure that the reaction fully yields the MN4 type half-metal.

[0062] In one embodiment, the predetermined pressure is 10 - 20 GPa.

[0063] In one embodiment, the predetermined temperature is 40 - 300 °C.

[0064] In one embodiment, the predetermined time is 2 - 4 h.

[0065] In step S11, the metal oxide nanoparticles and the MN4 type half-metal are dissolved in a third organic solvent, reacted under stirring, and after standing, washed and dried to obtain a composite material in which the MN4 type half-metal is combined with the metal oxide.

[0066] In one embodiment, on a molar ratio basis, the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is 1:(0.2 - 0.5). Because when the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is less than 1:0.2, the amount of the MN4 type half-metal combined with the metal oxide nanoparticles is small, and the effect on improving the carrier transport performance of the metal oxide nanoparticles is not obvious. When the molar ratio of the metal oxide nanoparticles to the MN4 type half-metal is greater than 1:0.5, the proportion of the MN4 type half-metal component is large, while the proportion of the metal oxide nanoparticle component is small, and the carrier transport performance decreases.

[0067] In one embodiment, the temperature of the reaction is 60 - 80 °C.

[0068] In one embodiment, the time of the reaction is 2 - 4 h.

[0069] The embodiment of the present invention provides a quantum dot light emitting diode, which includes a hole transport layer, and the hole transport layer includes the composite material of the embodiment of the present invention;

[0070] Or, it includes an electron transport layer, and the electron transport layer includes the composite material of the embodiment of the present invention.

[0071] In this embodiment, the quantum dot light emitting diode has various forms, and the quantum dot light emitting diode is divided into a normal structure and an inverted structure. The embodiment of the present invention will mainly take the quantum dot light emitting diode with the normal structure as shown in Figure 3 as an example for detailed introduction. As shown in Figure 3As shown in the figure, the quantum dot light-emitting diode of the embodiment of the present invention includes a substrate 1, an anode 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5, and a cathode 6. Among them, the hole transport layer 3 or the electron transport layer 5 includes the composite material of the embodiment of the present invention.

[0072] In one embodiment, the composite material includes metal oxide nanoparticles and MN4-type half metals dispersed between the metal oxide nanoparticles. The metal oxide nanoparticles are combined with the MN4-type half metals, where M in the MN4-type half metals is a metal atom with a 3d electron orbital in the outermost layer.

[0073] In one embodiment, the composite material is composed of metal oxide nanoparticles and MN4-type half metals.

[0074] In one embodiment, hydroxyl ligands are bound to the surface of the metal oxide nanoparticles, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are coordinately bound to the metal elements on the surface of the MN4-type half metals.

[0075] In this embodiment, the MN4-type half metal material is a kind of material with a diamond-like structure constructed with MN4 tetrahedrons with M atoms as the center and N atoms occupying the vertex positions and N=N bonds as the building blocks (M in the MN4 tetrahedron is a metal atom with a 3d electron orbital in the outermost layer). Taking the FeN4-type half metal as an example, a diamond-like structure of the FeN4-type half metal is constructed with FeN4 tetrahedrons with Fe atoms as the center and N=N bonds as the building blocks. The π* bond (π antibond) in the N=N double bond provides a high concentration of delocalized electrons, which plays a decisive role in the conductivity of this material, and its conductivity is as high as 5.07×10 5 S / cm. On the one hand, the N=N bond provides a bridge for carrier transport. On the other hand, the tetrahedron formed by N atoms and M metal atoms causes the splitting of the 3d electron orbital under the action of the crystal field. The two are further hybridized to form bonds, so that the energy state in a certain spin direction is split into a bonding state and an antibonding state, thereby opening the band gap, making the band gap of such MN4-type half metals greater than 2 eV, and thus can be used in the application of semiconductor electronics devices.

[0076] In addition, due to their small particle size, metal oxide nanoparticles tend to agglomerate. In this embodiment, after the MN4-type half-metal is combined with metal oxide nanoparticles, the metal oxide nanoparticles can be evenly dispersed by virtue of the property that the surface metal atoms in the half-metal are prone to coordinate with the hydroxyl ligands on the surface of the metal oxide nanoparticles. In addition, the MN4-type half-metal has a high electrical conductivity, and by combining with metal oxide nanoparticles, the electrical conductivity of the metal oxide nanoparticles can be improved. Moreover, the MN4-type half-metal has a small band gap, making it easier for the electrons in the composite material formed by the combination of the MN4-type half-metal and metal oxide nanoparticles to be excited from the valence band to the conduction band, increasing the carrier concentration, facilitating the transport of carriers, and improving the QLED luminescence efficiency.

[0077] In this embodiment, when the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material, the composite material is used as a hole transport layer material. The material of the electron transport layer can be selected from conventional materials with good electron transport performance, such as but not limited to one or more of n-type ZnO, TiO2, Fe2O3, SnO2, Ta2O3, AlZnO, ZnSnO, InSnO, etc.

[0078] In this embodiment, when the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material, the composite material is used as an electron transport layer material. The material of the hole transport layer can be selected from conventional materials with good hole transport performance, such as but not limited to one or more of TFB, PVK, Poly-TPD, TCTA, PEDOT:PSS, CBP, etc.

[0079] In one embodiment, the thickness of the hole transport layer is 20 - 60 nm. If the thickness of the hole transport layer is too thin, the transport performance of carriers cannot be guaranteed, resulting in hole-electron recombination in the transport layer due to the inability of holes to reach the quantum dot light-emitting layer, thereby causing quenching; if the thickness of the hole transport layer is too thick, the light transmittance of the film layer will decrease, and the carrier passability of the device will be reduced, resulting in a decrease in the overall conductivity of the device.

[0080] In one embodiment, the substrate can be a substrate of rigid material, such as glass, etc., or a substrate of flexible material, such as one of PET or PI, etc.

[0081] In one embodiment, the anode can be selected from one or more of indium-doped tin oxide (ITO), fluorine-doped tin oxide (FTO), antimony-doped tin oxide (ATO), and aluminum-doped zinc oxide (AZO), etc.

[0082] In one embodiment, the luminescent quantum dots of the quantum dot light-emitting layer are oil-soluble luminescent quantum dots, and the oil-soluble luminescent quantum dots include binary-phase, ternary-phase, and quaternary-phase quantum dots; among them, the binary-phase quantum dots include CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, HgS, etc. (not limited thereto), the ternary-phase quantum dots include ZnCdS, CuInS, ZnCdSe, ZnSeS, ZnCdTe, PbSeS, etc. (not limited thereto), and the quaternary-phase quantum dots include ZnCdS / ZnSe, CuInS / ZnS, ZnCdSe / ZnS, CuInSeS, ZnCdTe / ZnS, PbSeS / ZnS, etc. (not limited thereto). The luminescent quantum dots can be selected from one of the common red, green, and blue quantum dots, or can be yellow-light quantum dots. The quantum dots can contain cadmium or not contain cadmium. The quantum dot light-emitting layer has characteristics such as a wide and continuously distributed excitation spectrum and high emission spectrum stability.

[0083] In one embodiment, the cathode can be selected from one of an aluminum (Al) electrode, a silver (Ag) electrode, a gold (Au) electrode, etc., and can also be selected from one of nano-aluminum wires, nano-silver wires, nano-gold wires, etc.

[0084] It should be noted that the quantum dot light-emitting diode of the present invention can also include one or more of the following functional layers: a hole injection layer disposed between the hole transport layer and the anode, and an electron injection layer disposed between the electron transport layer and the cathode.

[0085] The embodiment of the present invention provides a method for preparing a quantum dot light-emitting diode, which includes the steps:

[0086] Prepare a hole transport layer, and the material of the hole transport layer includes the composite material of the embodiment of the present invention;

[0087] Alternatively, prepare an electron transport layer whose material includes the composite material of the embodiment of the present invention.

[0088] Next, taking Figure 3 the quantum dot light-emitting diode with the structure shown as an example, the method for preparing the quantum dot light-emitting diode will be introduced in detail. As Figure 4 shown, the method for preparing the quantum dot light-emitting diode of this embodiment includes the steps:

[0089] S20. Form a hole transport layer on the anode (formed on the substrate);

[0090] S21. Form a quantum dot light-emitting layer on the hole transport layer;

[0091] S22. Form an electron transport layer on the quantum dot light-emitting layer;

[0092] S23. Form a cathode on the electron transport layer to obtain a quantum dot light-emitting diode.

[0093] In the embodiments of the present invention, the preparation method of the composite material is as described above and will not be elaborated here.

[0094] In step S20, in order to obtain a high-quality hole transport layer, the anode needs to undergo a pretreatment process. The pretreatment process specifically includes: cleaning the anode with a cleaner to initially remove the stains on the surface of the anode, and then ultrasonically cleaning in deionized water, acetone, absolute ethanol, and deionized water for 20 minutes respectively to remove the impurities on the surface. Finally, it is dried with high-purity nitrogen to obtain the anode.

[0095] In one embodiment, preparation methods such as spin coating, dip coating, immersion coating, printing, evaporation coating, etc., which are not limited to this, can be used to form a hole transport layer on the anode. This preparation method is applicable to existing conventional hole transport materials and also to the composite materials of the embodiments of the present invention.

[0096] In one embodiment, step S20 specifically includes: spin coating the solution of the prepared hole transport layer material on the anode, and then performing thermal annealing treatment at 300 - 350 °C to obtain the hole transport layer. Among them, the film thickness can be controlled by adjusting the concentration of the solution, the spin coating speed, and the spin coating time, and the thickness of the hole transport layer can be 20 - 60 nm.

[0097] In one embodiment, step S21 specifically includes: placing the substrate with the spin-coated hole transport layer on a spin coater, spin coating the solution of the prepared luminescent quantum dots on the hole transport layer, and then performing thermal annealing treatment to obtain the quantum dot light-emitting layer. Among them, the film thickness can be controlled by adjusting the concentration of the solution, the spin coating speed, and the spin coating time, and the thickness of the quantum dot light-emitting layer can be 20 - 60 nm.

[0098] In one embodiment, preparation methods such as spin coating, dip coating, immersion coating, printing, evaporation coating, etc., which are not limited to this, can be used to form an electron transport layer on the quantum dot light-emitting layer. This preparation method is applicable to existing conventional electron transport materials and also to the composite materials of the embodiments of the present invention.

[0099] In one embodiment, step S22 specifically includes: placing the substrate with the spin-coated quantum dot light-emitting layer on a spin coater, spin coating the solution of the prepared electron transport layer material on the quantum dot light-emitting layer, and then performing thermal annealing treatment at 200 - 300 °C to obtain the electron transport layer. Among them, the film thickness can be controlled by adjusting the concentration of the solution, the spin coating speed, and the spin coating time, and the thickness of the electron transport layer can be 20 - 60 nm. Among them, annealing can be carried out in air or in a nitrogen atmosphere, and the annealing atmosphere is specifically selected according to actual needs.

[0100] In one embodiment, step S23 specifically includes: placing the substrate with all functional layers deposited therein into an evaporation chamber, and thermally evaporating a cathode material layer with a thickness of 15 - 30 nm through a mask plate to obtain a cathode. The cathode material can be metallic silver or aluminum, or nano Ag wires or Cu wires, which have a relatively small resistance to enable the smooth injection of carriers.

[0101] In one embodiment, the obtained quantum dot light-emitting diode is subjected to a packaging process. The packaging process can be carried out by using a common machine packaging method or a manual packaging method. Among them, in the environment of the packaging process, both the oxygen content and the water content are lower than 0.1 ppm to ensure the stability of the device.

[0102] The present invention will be further described in detail below through specific embodiments.

[0103] Example 1

[0104] In this example, the preparation steps of the composite material of FeN4 and ZnO are as follows:

[0105] 1), First, add an appropriate amount of zinc acetate to 50 ml of ethanol to form a solution with a total concentration of 0.5 M. Then, stir and dissolve at 70 °C, and add an alkaline solution (molar ratio, OH - : Zn 2+ = 2:1, pH = 12) prepared by dissolving potassium hydroxide in 10 ml of ethanol. Continue to stir at 70 °C for 4 h to obtain a uniform transparent solution. Subsequently, after the solution is cooled, it is precipitated with ethyl acetate, centrifuged, dissolved in a small amount of ethanol, and the precipitation and dissolution steps are repeated 3 times, and then dried to obtain ZnO nanoparticles;

[0106] 2), Dissolve an appropriate amount of FeCl3 and ammonium chloride in 10 ml of dimethyl sulfoxide (molar ratio, Fe:N = 1:5). After ultrasonic dissolution, transfer the mixed solution to a high-pressure and high-temperature reaction kettle. First, apply a high pressure of 10 GPa to the reaction raw materials. After the pressure rises to the predetermined pressure, heat it up to 300 °C and keep it at a constant temperature and pressure for 2 h. Finally, cool it down at a fixed pressure, and after cooling to room temperature, carry out a pressure relief treatment to obtain an FeN4-type half-metal;

[0107] 3), Add the ZnO nanoparticles and the FeN4-type half-metal to 30 ml of ethanol to form a solution with a total concentration of 0.5 M, where the molar ratio of ZnO:FeN4 is 1:0.5. Then, stir and react at 70 °C for 2 h. After standing, wash, dry, and obtain the composite material of FeN4 and ZnO.

[0108] Example 2

[0109] In this example, the preparation steps of the composite material of MnN4 and TiO2 are as follows:

[0110] 1), First, add an appropriate amount of titanium nitrate to 50 ml of methanol to form a solution with a total concentration of 0.8 M. Then stir and dissolve at 60 °C, and add a solution of sodium hydroxide dissolved in 10 ml of methanol (molar ratio, OH - : Ti 4+ = 2.5:1). Continue to stir at 60 °C for 4 h to obtain a homogeneous solution. Subsequently, after the solution cools, precipitate with ethyl acetate, dissolve in a small amount of methanol after centrifugation, repeat the precipitation and dissolution steps 3 times, and dry to obtain TiO2 nanoparticles;

[0111] 2), Dissolve an appropriate amount of MnCl2 and urea in 10 mL of N,N-dimethylformamide (molar ratio, Mn:N = 1:6). After ultrasonic dissolution, transfer the mixed solution to a high-pressure and high-temperature reaction kettle. First, apply a high pressure of 12 GPa to the reaction raw materials. After the pressure rises to the predetermined pressure, heat up to 350 °C and keep the temperature and pressure constant for 3 h. Finally, cool down at a fixed pressure. After cooling to room temperature, perform pressure relief treatment to obtain MnN4-type half-metal;

[0112] 3), Add TiO2 nanoparticles and MnN4-type half-metal to 30 ml of ethanol to form a solution with a total concentration of 0.5 M, where the molar ratio of TiO2:MnN4 is 1:0.3. Then stir and react at 70 °C for 2 h. After standing, wash and dry to obtain a composite material of MnN4 and TiO2.

[0113] Example 3

[0114] The preparation steps of the composite material of CoN4 and NiO in this example are as follows:

[0115] 1), First, add an appropriate amount of nickel chloride to 50 ml of propanol to form a solution with a total concentration of 1 M. Then stir and dissolve at 80 °C, and add an alkaline solution prepared by dissolving lithium hydroxide in 10 ml of propanol (molar ratio, OH - : Ni 2+ = 2:1, pH = 12). Continue to stir at 80 °C for 4 h to obtain a homogeneous solution. Subsequently, after the solution cools, precipitate with ethyl acetate, dissolve in a small amount of ethanol after centrifugation, repeat the precipitation and dissolution steps 3 times, and dry to obtain NiO nanoparticles;

[0116] 2), Dissolve an appropriate amount of CoCl2 and urea in 10 mL of tetrahydrofuran (molar ratio, Co:N = 1:7). After ultrasonic dissolution, transfer the mixed solution to a high-pressure and high-temperature reaction kettle. First, apply a high pressure of 15 GPa to the reaction raw materials. After the pressure rises to the predetermined pressure, heat up to 400 °C and keep the temperature and pressure constant for 2 h. Finally, cool down at a fixed pressure. After cooling to room temperature, perform pressure relief treatment to obtain CoN4-type half-metal;

[0117] 3), NiO nanoparticles and CoN4-type half metals were added to 30 ml of ethanol to form a solution with a total concentration of 0.5 M, where the molar ratio of NiO:CoN4 was 1:0.2. Then, the mixture was stirred and reacted at 70 °C for 2 h. After standing, it was washed and dried to obtain a composite material of CoN4 and NiO.

[0118] Example 4

[0119] A positive-type quantum dot light-emitting diode includes a stacked structure of an anode and a cathode disposed opposite to each other, a quantum dot light-emitting layer disposed between the anode and the cathode, an electron transport layer disposed between the cathode and the quantum dot light-emitting layer, a hole transport layer disposed between the anode and the quantum dot light-emitting layer, and the anode is disposed on a substrate. Among them, the material of the substrate is a glass sheet with a thickness of 2 μm, the material of the anode is ITO with a thickness of 50 nm, the material of the hole transport layer is TFB with a thickness of 40 nm, the material of the quantum dot light-emitting layer is CdZnS / ZnS with a thickness of 40 nm, the material of the electron transport layer is a composite material of FeN4 and ZnO obtained by the method of Example 1 with a thickness of 80 nm, and the material of the cathode is Al with a thickness of 80 nm.

[0120] The preparation method of the quantum dot light-emitting diode includes the following steps:

[0121] Provide an ITO substrate and prepare a hole transport layer on the ITO substrate;

[0122] Prepare a quantum dot light-emitting layer on the hole transport layer;

[0123] Deposit the composite material of FeN4 and ZnO obtained by the method of Example 1 on the quantum dot light-emitting layer to prepare an electron transport layer;

[0124] Prepare a cathode on the electron transport layer.

[0125] Example 5

[0126] This example is basically the same as Example 4, except that: the material of the electron transport layer is the composite material of MnN4 and TiO2 obtained by the method of Example 2.

[0127] Example 6

[0128] This example is basically the same as Example 4, except that: the material of the hole transport layer is the composite material of CoN4 and NiO obtained by the method of Example 3, and the material of the electron transport layer is ZnO.

[0129] Example 7

[0130] An inverted-structure quantum dot light-emitting diode includes a stacked structure of an anode and a cathode arranged opposite to each other, a quantum dot light-emitting layer disposed between the anode and the cathode, an electron transport layer disposed between the cathode and the quantum dot light-emitting layer, a hole transport layer disposed between the anode and the quantum dot light-emitting layer, and the cathode is disposed on a substrate. Among them, the material of the substrate is a glass sheet with a thickness of 2 μm, the material of the cathode is ITO with a thickness of 50 nm, the material of the hole transport layer is TFB with a thickness of 40 nm, the material of the quantum dot light-emitting layer is CdZnS / ZnS with a thickness of 40 nm, the material of the electron transport layer is a composite material of FeN4 and ZnO, with a thickness of 80 nm, and the material of the anode is Al with a thickness of 80 nm.

[0131] The preparation method of the quantum dot light-emitting diode includes the following steps:

[0132] Provide an ITO substrate, deposit the composite material of FeN4 and ZnO obtained in the method of Example 1 on the ITO substrate to prepare an electron transport layer;

[0133] Prepare a quantum dot light-emitting layer on the electron transport layer;

[0134] Prepare a hole transport layer on the quantum dot light-emitting layer;

[0135] Prepare an anode on the hole transport layer.

[0136] Example 8

[0137] This example is basically the same as Example 7, the difference is that: the material of the electron transport layer is the composite material of MnN4 and TiO2 obtained in the method of Example 2.

[0138] Example 9

[0139] This example is basically the same as Example 7, the difference is that: the material of the hole transport layer is the composite material of CoN4 and NiO obtained in the method of Example 3, and the material of the electron transport layer is ZnO.

[0140] Comparative Example 1

[0141] This comparative example is basically the same as Example 4, the difference is that: the material of the electron transport layer is a commercial ZnO material (purchased from sigma company).

[0142] Comparative Example 2

[0143] This comparative example is basically the same as Example 4, the difference is that: the material of the electron transport layer is a commercial TiO2 material (purchased from sigma company).

[0144] Comparative Example 3

[0145] This comparative example is basically the same as Example 9, except that the material of the hole transport layer is a commercial NiO material (purchased from sigma).

[0146] Perform performance tests on the electron transport thin films prepared in Examples 1-2, the hole transport thin films prepared in Example 3, the electron transport thin films in Comparative Examples 1-2, the hole transport thin films in Comparative Example 3, and the quantum dot light-emitting diodes prepared in Examples 4-9 and Comparative Examples 1-3. The test indicators and test methods are as follows:

[0147] (1) Electron mobility: Measure the current density (J)-voltage (V) of the electron transport thin film, plot a curve relationship diagram, fit the space charge limited current (SCLC) region in the relationship diagram, and then calculate the electron mobility according to the famous Child , 's law formula:

[0148] J = (9 / 8)ε r ε0μ e V 2 / d 3

[0149] where J represents the current density, in mAcm -2 ; ε r represents the relative dielectric constant, ε0 represents the vacuum dielectric constant; μ e represents the electron mobility, in cm 2 V -1 s -1 ; V represents the driving voltage, in V; d represents the film thickness, in m.

[0150] (2) Hole mobility: Measure the current density (J)-voltage (V) of the hole transport thin film, plot a curve relationship diagram, fit the space charge limited current (SCLC) region in the relationship diagram, and then calculate the hole mobility according to the famous Child’s law formula:

[0151] J = (9 / 8)ε r ε0μ e V 2 / d 3

[0152] where J represents the current density, in mAcm -2 ; ε r represents the relative dielectric constant, ε0 represents the vacuum dielectric constant; μ e represents the hole mobility, in cm 2 V -1 s -1; V represents the driving voltage, with the unit of V; d represents the film thickness, with the unit of m.

[0153] (3) Resistivity: The resistivity of the electron transport thin film is measured using the same resistivity testing instrument.

[0154] (4) External quantum efficiency (EQE): It is measured using an EQE optical testing instrument.

[0155] Note: The measurements of electron mobility, hole mobility, and resistivity are for single-layer thin film structure devices, i.e., cathode / electron (hole) transport thin film / anode. The external quantum efficiency measurement is for the QLED device described above, i.e., anode / hole transport thin film / quantum dot light-emitting layer / electron transport thin film / cathode, or cathode / electron transport thin film / quantum dot light-emitting layer / hole transport thin film / anode.

[0156] The test results are shown in Table 1 below:

[0157] Table 1

[0158]

[0159] As can be seen from Table 1 above, for the electron transport thin film (hole transport thin film) which is a composite material of MN4 and metal oxide provided in Embodiments 1-3 of the present invention, the resistivity is significantly lower than that of the electron transport thin film (hole transport thin film) made of metal oxide composite materials in Comparative Examples 1-3, while the electron mobility (hole mobility) is significantly higher than the mobility of the electron transport thin film (hole transport thin film) made of metal oxide composite materials in Comparative Examples 1-3.

[0160] The external quantum efficiency of the quantum dot light-emitting diodes (composite materials of MN4-type semimetal and metal oxide) provided in Embodiments 4-9 of the present invention is significantly higher than that of the quantum dot light-emitting diodes made of metal oxide composite materials in Comparative Examples 1-3, indicating that the quantum dot light-emitting diodes obtained in the embodiments have better luminous efficiency.

[0161] It should be noted that the specific embodiments provided by the present invention all use the blue light quantum dot Cd X Zn 1-X S / ZnS as the light-emitting layer material, which is based on a blue light emission system and is a more commonly used system (since it is more difficult for blue light quantum dot light-emitting diodes to achieve high efficiency, it is more valuable for reference), and does not mean that the present invention is only applicable to the blue light emission system.

[0162] It should be understood that the application of the present invention is not limited to the above examples. For those of ordinary skill in the art, improvements or transformations can be made according to the above description, and all such improvements and transformations should fall within the protection scope of the appended claims of the present invention.

Claims

1. A composite material, characterized in that, It includes metal oxide nanoparticles and MN4-type half-metals. The metal oxide nanoparticles are combined with the MN4-type half-metals, where M in the MN4-type half-metal is a metal atom with an outermost 3d electron orbital. The MN4-type half-metal is selected from FeN4-type half-metals, CoN4-type half-metals, or MnN4-type half-metals. Hydroxyl ligands are bound to the surface of the metal oxide nanoparticles, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are coordinately bound to the metal elements on the surface of the MN4-type half-metal. The metal oxide nanoparticles are metal oxide nanoparticles used as electron transport materials; or the metal oxide nanoparticles are metal oxide nanoparticles used as hole transport materials.

2. The composite material according to claim 1, characterized in that, The metal oxide nanoparticles used as electron transport materials are selected from one or more of ZnO nanoparticles, TiO2 nanoparticles, SnO nanoparticles, and SnO2 nanoparticles. Alternatively, the metal oxide nanoparticles used as hole transport materials are selected from one or more of WO3 nanoparticles, MoO3 nanoparticles, NiO nanoparticles, Cu2O nanoparticles, ReO3 nanoparticles, and V2O5 nanoparticles.

3. The composite material according to claim 1, characterized in that, The molar ratio of the metal oxide nanoparticles to the MN4-type half-metal is 1:(0.2 - 0.5).

4. A method for preparing the composite material according to any one of claims 1 to 3, characterized in that, It includes the steps: Provide metal oxide nanoparticles and MN4-type half-metals, where M in the MN4-type half-metal is a metal atom with an outermost 3d electron orbital; the MN4-type half-metal is selected from FeN4-type half-metals, CoN4-type half-metals, or MnN4-type half-metals; hydroxyl ligands are bound to the surface of the metal oxide nanoparticles, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are coordinately bound to the metal elements on the surface of the MN4-type half-metal. Mix the metal oxide nanoparticles and the MN4-type half-metals in an organic solvent and react under stirring to obtain a composite material in which the metal oxide nanoparticles and the MN4-type half-metals are combined.

5. The preparation method of the composite material according to claim 4, characterized in that, The reaction temperature is 60 - 80 °C, and / or the reaction time is 2 - 4 h.

6. A quantum dot light emitting diode, characterized in that, It includes a hole transport layer, and the hole transport layer includes the composite material described in any one of claims 1 - 3. Alternatively, it includes an electron transport layer, and the electron transport layer includes the composite material described in any one of claims 1 - 3.

7. A preparation method of a quantum dot light-emitting diode, characterized in that, It includes the steps: Prepare a hole transport layer, and the material of the hole transport layer includes the composite material described in any one of claims 1 - 3. Alternatively, prepare an electron transport layer, and the material of the electron transport layer includes the composite material described in any one of claims 1 - 3.

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