CN114695750A

CN114695750A - Composite material, quantum dot light-emitting diode and preparation method thereof

Info

Publication number: CN114695750A
Application number: CN202011644189.XA
Authority: CN
Inventors: 何斯纳; 吴龙佳; 吴劲衡
Original assignee: TCL Technology Group Co Ltd
Current assignee: TCL Technology Group Co Ltd
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-07-01

Abstract

The invention discloses a composite material, a quantum dot light-emitting diode and a preparation method thereof. The composite material comprises metal oxide nanoparticles and MN₄Type semimetal, metal oxide nanoparticles and MN₄Type of semimetal binding, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit. The invention connects MN₄After the semimetal and the metal oxide nanoparticles are compounded, the metal oxide nanoparticles can be uniformly dispersed by utilizing the characteristic that surface metal atoms in the semimetal are easy to coordinate with hydroxyl ligands on the surfaces of the metal oxide nanoparticles. MN (Mobile node)₄The semimetal has higher conductivity, and the conductivity of the semimetal can be improved by compounding the semimetal with metal oxide nanoparticles. MN (Mobile node)₄The band gap of the type semimetal is small, so that the type semimetal and the metal oxygen are mixedElectrons of the composite material combined by the compound nano particles are easier to be excited from a valence band to a conduction band, the carrier concentration is increased, the carrier transmission is facilitated, and the luminous efficiency of the device is improved.

Description

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

Technical Field

The invention relates to the field of quantum dot light-emitting diodes, in particular to a composite material, a quantum dot light-emitting diode and a preparation method thereof.

Background

The semiconductor Quantum Dots (QDs) have quantum size effect, the required luminescence with specific wavelength can be realized by regulating the size of the quantum dots, and the tuning range of the luminescence wavelength of the CdSe QDs can be from blue light to red light. In the conventional inorganic electroluminescent device, electrons and holes are injected from a cathode and an anode, respectively, and then recombined in a light emitting layer to form excitons for light emission.

In recent years, inorganic semiconductors have been studied as an electron transport layer or a hole transport layer, which is relatively hot. Nano ZnO, TiO₂、SnO₂The material is a wide-bandgap semiconductor material, attracts a plurality of researchers due to the advantages of quantum confinement effect, size effect, excellent fluorescence characteristic and the like, and is often used as an electron transport layer. In addition, transition metal oxides (WO)₃、MoO₃、NiO、Cu₂O、ReO₃And V₂O₅) Is used as a hole transport layer in many quantum dot light emitting diodes (QLEDs) and achieves good performance. However, the carrier transport efficiency of the inorganic metal oxide semiconductor material used as an electron transport layer or a hole transport layer of the QLED is still low during the application process, which results in low device efficiency.

Accordingly, the prior art remains to be improved and developed.

Disclosure of Invention

In view of the above-mentioned shortcomings of the prior art, the present invention aims to provide a composite material, a quantum dot light emitting diode and a preparation method thereof, which aim to solve the problem that the carrier transport efficiency of the existing inorganic metal oxide as a charge transport material is still low.

The technical scheme of the invention is as follows:

in a first aspect of the invention, there is provided a composite material comprising metal oxide nanoparticles and MN₄Type semimetal, metal oxide nanoparticles and MN₄Type of semimetal binding, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit.

Optionally, the metal oxide nanoparticles have hydroxyl ligands bound to the surfaceHydroxyl ligands on the surface of metal oxide nanoparticles and MN₄And (3) coordinating and combining metal elements on the surface of the semi-metal.

Alternatively, the MN₄The type semimetal is selected from FeN₄Type semimetal, CoN₄Type semimetal, MnN₄Type semimetal and AlN₄One or more of type semi-metals.

Alternatively, the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material; alternatively, the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material.

Optionally, the metal oxide nanoparticles used as electron transport material are selected from ZnO nanoparticles, TiO nanoparticles₂Nanoparticles, SnO₂One or more of nanoparticles;

alternatively, the metal oxide nanoparticles used as hole transport material are selected from WO₃Nanoparticles, MoO₃Nanoparticles, NiO nanoparticles, Cu₂O nanoparticles, ReO₃Nanoparticles and V₂O₅One or more of the nanoparticles.

Optionally, the metal oxide nanoparticles are associated with MN₄The molar ratio of the type-II semimetal is 1: (0.2-0.5).

In a second aspect of the present invention, there is provided a method for preparing the composite material of the present invention, wherein the method comprises the steps of:

providing metal oxide nanoparticles and MN₄Type II semimetals, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit;

mixing metal oxide nanoparticles with MN₄Mixing the semimetal in organic solvent, and reacting under stirring to obtain metal oxide nanoparticles and MN₄A semi-metal bonded composite.

Optionally, the reaction temperature is 60-80 ℃, and/or the reaction time is 2-4 h.

In a third aspect of the invention, a quantum dot light emitting diode is provided, wherein the quantum dot light emitting diode comprises a hole transport layer, and the hole transport layer comprises the composite material of the invention;

alternatively, an electron transport layer is included, the electron transport layer comprising the composite material of the present invention.

The fourth aspect of the present invention provides a method for manufacturing a quantum dot light emitting diode, wherein the method comprises the steps of:

preparing a hole transport layer, wherein the material of the hole transport layer comprises the composite material;

alternatively, an electron transport layer is prepared, the material of the electron transport layer comprising the composite material of the present invention.

Has the advantages that: in the present invention, the metal oxide nanoparticles are easily agglomerated due to small particle size by mixing MN₄After the semi-metal and the metal oxide nano-particles are compounded, the metal oxide nano-particles can be uniformly dispersed by utilizing the characteristic that surface metal atoms in the semi-metal are easy to coordinate with hydroxyl ligands on the surfaces of the metal oxide nano-particles, and the agglomeration among the metal oxide nano-particles is effectively avoided. In addition, MN₄The semimetal has higher conductivity, and the conductivity of the metal oxide nanoparticles can be improved by compounding the semimetal with the metal oxide nanoparticles. In addition, MN₄The band gap of the type semimetal is smaller, so that MN₄Electrons of the composite material formed by compounding the type semimetal and the metal oxide nanoparticles are easier to be excited to a conduction band from a valence band, so that the carrier concentration is increased, the transmission of carriers is facilitated, and the luminous efficiency of the QLED is improved.

Drawings

FIG. 1 shows FeN₄Chemical structural formula of semimetal.

Fig. 2 is a schematic flow chart of a method for preparing a composite material according to an embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a quantum dot light emitting diode according to an embodiment of the present invention.

Fig. 4 is a schematic flow chart of a method for manufacturing a quantum dot light emitting diode according to an embodiment of the present invention.

Detailed Description

The invention provides a composite material, a quantum dot light-emitting diode and a preparation method thereof, and the invention is further described in detail below in order to make the purpose, technical scheme and effect of the invention clearer and clearer. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

The inventor unexpectedly finds that the semimetal (half metal) material has wide application prospect in the aspect of electronic devices due to the characteristic that one spin direction of the semimetal material is the metal conducting behavior, and the other spin direction of the semimetal material is the semiconductor conducting behavior. In the conventional half-metal band structure, the conduction band and the valence band have a small overlap (a small negative energy gap) or are just tangent (a zero energy gap), so that the half-metal macroscopic carrier transport performance is weaker than that of a typical metal and stronger than that of a typical semiconductor. Further research shows that the carrier transmission efficiency of the metal oxide nanoparticles can be improved by compounding the semimetal material and the metal oxide nanoparticles as an electron (hole) transmission layer.

Based on the above, the embodiment of the invention provides a composite material, which comprises metal oxide nanoparticles and MN₄Type semimetal, metal oxide nanoparticles and MN₄Type of semimetal binding, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit.

In one embodiment, the composite material is composed of metal oxide nanoparticles and MN₄And (3) a type semimetal.

In one embodiment, the metal oxide nanoparticles have hydroxyl ligands bound to the surface thereof, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are bound to MN₄And (3) coordinating and combining metal elements on the surface of the semi-metal.

In this embodiment, MN₄The type semi-metal material is MN with M atom as center and N atom occupying vertex position₄Class of diamond-like structures built with tetrahedral and N ═ N bonds as elements (MN)₄M in the tetrahedron is a metal atom with an outermost 3d electron orbital). With FeN₄type-II semimetals, e.g. by FeN centred on Fe atoms₄FeN with tetrahedron and N-N bond as basic elements to construct diamond-like structure₄And (3) a type semimetal, as shown in figure 1. The pi-bonds (pi-inversions) in the N-N double bonds provide high concentrations of delocalized electrons, which are decisive for the conductivity of the material, up to 5.07 × 10⁵S/cm. N-N bond provides a bridge for carrier transport on one hand, and on the other hand, a tetrahedron formed by N atoms and M metal atoms enables a 3d electron orbit to be split under the action of a crystal field, the N atoms and the M metal atoms are further hybridized into bonds, so that an energy state in a certain spinning direction is split into a bonding state and a reverse bonding state, and a band gap is opened, so that the MN is obtained by splitting the energy state in the certain spinning direction into a bonding state and a reverse bonding state₄The band gap of the type semimetal is larger than 2eV, so that the type semimetal can be used in the application of semiconductor electronic devices.

In addition, the metal oxide nanoparticles are easily agglomerated due to their small particle size. This embodiment will MN₄After the semi-metal and the metal oxide nano-particles are compounded, the metal oxide nano-particles can be uniformly dispersed by utilizing the characteristic that surface metal atoms in the semi-metal are easy to coordinate with hydroxyl ligands on the surfaces of the metal oxide nano-particles, and the agglomeration among the metal oxide nano-particles is effectively avoided. In addition, MN₄The semimetal has higher conductivity, and the conductivity of the metal oxide nanoparticles can be improved by compounding the semimetal with the metal oxide nanoparticles. And, MN₄The band gap of the type semimetal is smaller, so that MN₄Electrons of the composite material formed by compounding the type semimetal and the metal oxide nanoparticles are easier to be excited to a conduction band from a valence band, so that the carrier concentration is increased, the transmission of carriers is facilitated, and the light-emitting efficiency of the QLED is improved.

In one embodiment, the MN₄The type semimetal may be selected from FeN₄Type semimetal, CoN₄Type semi-metal, MnN₄Type semimetal and AlN₄Type semimetal, and the like, but is not limited thereto.

In one embodiment, the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material; alternatively, the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material.

In one embodiment, the metal oxide nanoparticles used as electron transport material may be selected from ZnO nanoparticles, TiO nanoparticles₂Nanoparticles, SnO₂Nanoparticles, etc., but are not limited thereto.

In one embodiment, the metal oxide nanoparticles used as hole transport materials may be selected from WO₃Nanoparticles, MoO₃Nanoparticles, NiO nanoparticles, Cu₂O nanoparticles, ReO₃Nanoparticles and V₂O₅Nanoparticles, etc., but are not limited thereto.

In one embodiment, the metal oxide nanoparticles are mixed with MN₄The molar ratio of the type-II semimetal is 1: (0.2-0.5). Because when the metal oxide nanoparticles and MN₄The molar ratio of the type-II semimetal is less than 1: at 0.2 hour, MN₄The amount of the composite of the semimetal and the metal oxide nano particles is less, and the effect of improving the carrier transmission performance of the metal oxide nano particles is not obvious. When the metal oxide nanoparticles and MN₄The molar ratio of the type-II semimetal is more than 1: 0.5, MN₄The semi-metal has more components, while the metal oxide nanoparticles have less components, and the carrier transport performance is reduced.

The embodiment of the invention provides a preparation method of a composite material, which comprises the following steps of:

s10, providing metal oxide nanoparticles and MN₄Type II semimetals, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit;

s11, mixing metal oxide nano particles and MN₄Mixing the semimetal in organic solvent, stirring to react to obtain metal oxide nanoparticles and MN₄A semi-metal bonded composite.

In step S10, in one embodiment, a method for preparing metal oxide nanoparticles includes the steps of: dissolving metal salt in a first organic solvent, stirring, adding alkali liquor, continuing stirring, cooling, separating out by using a precipitator, washing, and drying to obtain the metal oxide nanoparticles.

In this example, the hydroxide (M (OH) is formed by the reaction of a metal salt with an alkaline solution_x)，M(OH)_xCondensation polymerization reaction is carried out, and MO is generated by dehydration_xAnd M represents a metal.

In one embodiment, OH in the lye^-The molar ratio of the metal ions to the metal ions in the metal salt is (1.8-4.5): 1, the pH value of the alkali liquor is 12-13. The dosage of the alkali liquor is adjusted according to the valence state of the metal ions. E.g. metal ions of +2 (Zn)²⁺、Ni²⁺) And then, the molar ratio of the alkali liquor to the metal ions is 2: 1, so that the molar ratio of the alkali liquor to the metal ions is kept between 1.8 and 2.5: 1, metal oxide nanoparticles can be generated. Such as when the metal ion is +4 (Ti)⁴⁺、Sn⁴⁺、Zr⁴⁺) The molar ratio of the alkali liquor to the metal ions is 4: 1, so that the molar ratio of the alkali liquor to the metal ions is kept between (3.5 and 4.5): 1, metal oxide nanoparticles can be generated. When the molar ratio of the alkali liquor to the metal ions is less than 1.8: 1 or 3.5: 1, pH<When 12 hours, alkali liquor is insufficient, metal salt is excessive, and reaction is insufficient; greater than 2.5: 1 or 4.5: 1, pH>At 13, too high a pH will result in a slow hydrolysis and polycondensation rate of the sol in the system. Therefore, the molar ratio of the alkali liquor to the metal ions is kept between 1.8 and 4.5: 1, the reaction can be ensured to be sufficient to obtain metal oxide nanoparticles.

In one embodiment, the metal salt solution has a concentration of 0.2 to 1M. Wherein the metal salt solution refers to a solution in which a metal salt is dissolved in an organic solvent.

In one embodiment, the alkali solution is added and then stirred at a temperature of 60-80 ℃.

In one embodiment, the time for stirring is 2 to 4 hours after the addition of the alkali solution.

In one embodiment, the metal salt may be one or more of a titanium salt, a zinc salt, a tin salt, a zirconium salt, a nickel salt, a tungsten salt, and the like, but is not limited thereto. In particular to precursor salt corresponding to metal oxide which can be used as an electron transport layer material or a hole transport layer material.

In one embodiment, the zinc salt may be a soluble inorganic or organic zinc salt, such as one or more of zinc acetate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate dihydrate, and the like, but is not limited thereto.

In one embodiment, the titanium salt may be one or more of titanium nitrate, titanium chloride, titanium sulfate, titanium bromide, and the like, but is not limited thereto.

In one embodiment, the tin salt may be a soluble inorganic or organic tin salt, such as one or more of tin nitrate, tin chloride, tin sulfate, tin methane sulfonate, tin ethane sulfonate, tin propane sulfonate, and the like, but is not limited thereto.

In one embodiment, the nickel salt may be a soluble inorganic nickel salt or an organic nickel salt, such as one or more of nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate tetrahydrate, and the like, but is not limited thereto.

In one embodiment, the first organic solvent may be one or more of isopropyl alcohol, ethanol, propanol, butanol, methanol, etc., but is not limited thereto.

In this embodiment, the alkali solution is prepared by dissolving alkali in a first organic solvent. In one embodiment, the base may be one or more of ammonia, potassium hydroxide, sodium hydroxide, lithium hydroxide, ethanolamine, ethylene glycol, diethanolamine, triethanolamine, ethylenediamine, and the like, but is not limited thereto.

In one embodiment, the precipitant is a weakly polar or non-polar solvent such as, but not limited to, ethyl acetate, heptane, octane, and the like.

In step S10, in one embodiment, the MN₄The preparation method of the type semimetal comprises the following steps: dissolving metal salt and a nitrogen source in a second organic solvent, stirring, and transferring to a high-pressure high-temperature reaction kettle; firstly, applying high pressure to a reaction kettle, heating up after the pressure is increased to a preset pressure, preserving heat and maintaining pressure for a preset time after the temperature is increased to a preset temperature, finally cooling down under the preset pressure, and carrying out pressure relief treatment after the temperature is reduced to room temperature to prepare MN₄And (4) forming a semi-metal.

In respect of MN₄Details of type A semi-metals are as described aboveThe description is omitted here.

In one embodiment, the nitrogen source may be selected from one or more of urea, ammonium sulfate, ammonium nitrate, ammonium chloride, and the like, but is not limited thereto.

In one embodiment, the second organic solvent may be selected from one or more of aprotic polar solvents such as Tetrahydrofuran (THF), Dimethylformamide (DMF), Dimethylsulfoxide (DMSO), and the like, but is not limited thereto.

In one embodiment, the molar ratio of metal salt to nitrogen source is 1: (5-7). Because when the molar ratio of metal salt to nitrogen source is less than 1:5, the nitrogen source is insufficient, the metal salt is excessive, and MN is generated₄The reaction of (a) is not sufficient; when the molar ratio of metal salt to nitrogen source is greater than 1: when 7 is used, the nitrogen source is excessive, and therefore, an impurity compound is easily formed and is not easily removed. When the molar weight ratio of metal salt to nitrogen source is 1: (5-7) sufficient reaction can be ensured to obtain MN₄And (4) forming a semi-metal.

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

In one embodiment, the predetermined temperature is 40 to 300 ℃.

In one embodiment, the predetermined time is 2 to 4 hours.

In step S11, the metal oxide nanoparticles and MN₄Dissolving the type semimetal in a third organic solvent, reacting under stirring, standing, cleaning, and oven drying to obtain MN₄A composite of a type semimetal in combination with a metal oxide.

In one embodiment, the metal oxide nanoparticles and MN are present in a molar ratio₄The molar ratio of the type-II semimetal is 1: (0.2-0.5). Because when the metal oxide nanoparticles and MN₄The molar ratio of the type-II semimetal is less than 1: 0.2 hour, MN₄The amount of the composite of the semimetal and the metal oxide nano particles is less, and the effect of improving the carrier transmission performance of the metal oxide nano particles is not obvious. When the metal oxide nanoparticles and MN₄The molar ratio of the type-II semimetal is more than 1: at 0.5, MN₄The component ratio of the type semimetal is more, and the metal oxide is sodiumThe rice grains have a small proportion of components and the carrier transport performance is reduced.

In one embodiment, the reaction temperature is 60 to 80 ℃.

In one embodiment, the reaction time is 2 to 4 hours.

The embodiment of the invention provides a quantum dot light-emitting diode, which comprises a hole transport layer, wherein the hole transport layer comprises the composite material disclosed by the embodiment of the invention;

alternatively, an electron transport layer is included that includes the composite of embodiments of the present invention.

In the present embodiment, the quantum dot light emitting diode has various forms, and the quantum dot light emitting diode has a positive type structure and an inverse type structure, and the present embodiment will be described in detail mainly by taking the quantum dot light emitting diode with the positive type structure as shown in fig. 3 as an example. As shown in fig. 3, the quantum dot light emitting diode according to 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, where the hole transport layer 3 or the electron transport layer 5 includes the composite material according to the embodiment of the present invention.

In one embodiment, the composite material includes metal oxide nanoparticles and MN dispersed between the metal oxide nanoparticles₄Type semimetal, metal oxide nanoparticles and MN₄Type of semimetal binding, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit.

In one embodiment, the metal oxide nanoparticles have hydroxyl ligands bound to the surface thereof, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are bound to MN₄And (3) carrying out coordination bonding on the metal elements on the surface of the semi-metal.

In this embodiment, MN₄The semi-metal material is MN with M atom as center and N atom occupying the peak position₄Class of materials of diamond-like structure built with tetrahedron and N ═ N bonds as Motifs (MN)₄M in tetrahedron is 3d electricity as the outermost layerMetal atoms of the sub-orbitals). With FeN₄type-II semi-metals, e.g. by FeN centred on Fe atoms₄FeN with tetrahedron and N-N bond as basic elements to construct diamond-like structure₄And (4) forming a semi-metal. The pi-bonds (pi-inversions) in the N-N double bonds provide high concentrations of delocalized electrons, which are decisive for the conductivity of the material, up to 5.07 × 10⁵S/cm. N-N bond provides a bridge for carrier transport on one hand, and on the other hand, the tetrahedron formed by N atoms and M metal atoms enables the 3d electron orbit to be split under the action of a crystal field, the N-N bond and the tetrahedron are further hybridized into bond, so that the energy state in a certain spinning direction is split into a bonding state and an anti-bonding state, and then the band gap is opened, so that the MN is obtained₄The band gap of the type semimetal is larger than 2eV, so that the type semimetal can be used in the application of semiconductor electronic devices.

In addition, the metal oxide nanoparticles are easily agglomerated due to their small particle size. This embodiment will MN₄After the semimetal and the metal oxide nanoparticles are compounded, the metal oxide nanoparticles can be uniformly dispersed by utilizing the characteristic that surface metal atoms in the semimetal are easy to coordinate with hydroxyl ligands on the surfaces of the metal oxide nanoparticles. In addition, MN₄The semimetal has higher conductivity, and the conductivity of the metal oxide nanoparticles can be improved by compounding the semimetal with the metal oxide nanoparticles. And, MN₄The band gap of the type semimetal is smaller, so that MN₄Electrons of the composite material formed by compounding the type semimetal and the metal oxide nanoparticles are easier to be excited to a conduction band from a valence band, so that the carrier concentration is increased, the transmission of carriers is facilitated, and the luminous efficiency of the QLED is improved.

In the present 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 may be selected from conventional materials having good electron transport properties, such as but not limited to n-type ZnO, TiO₂、Fe₂O₃、SnO₂、Ta₂O₃One or more of AlZnO, ZnSnO, InSnO and the like.

In the present 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 may be selected from conventional materials having good hole transport properties, such as but not limited to TFB, PVK, Poly-TPD, TCTA, PEDOT: PSS, CBP, etc.

In one embodiment, the thickness of the hole transport layer is 20 to 60 nm. If the thickness of the hole transport layer is too thin, the transport performance of a current carrier cannot be ensured, so that holes cannot reach the quantum dot light-emitting layer to cause hole-electron recombination of the transport layer, and quenching is caused; if the hole transport layer is too thick, the light transmittance of the film layer decreases, and the carrier permeability of the device decreases, resulting in a decrease in the conductivity of the entire device.

In one embodiment, the substrate may be a rigid substrate, such as glass, or a flexible substrate, such as one of PET or PI.

In one embodiment, the anode may be selected from one or more of indium doped tin oxide (ITO), fluorine doped tin oxide (FTO), antimony doped tin oxide (ATO), aluminum doped zinc oxide (AZO), and the like.

In one embodiment, the light emitting quantum dots of the quantum dot light emitting layer are oil-soluble light emitting quantum dots, and the oil-soluble light emitting quantum dots comprise binary phase, ternary phase and quaternary phase quantum dots; wherein the binary phase quantum dots include, but are not limited to, CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, HgS, etc., the ternary phase quantum dots include, but are not limited to, ZnCdS, CuInS, ZnCdSe, ZnSeS, ZnCdTe, PbSeS, etc., and the quaternary phase quantum dots include, but are not limited to, ZnCdS/ZnSe, CuInS/ZnS, ZnCdSe/ZnS, CuInSeS, ZnCdTe/ZnS, PbSeS/ZnS, etc. The light-emitting quantum dots can be selected from one of red, green and blue quantum dots, and can also be yellow light quantum dots. The quantum dots may be cadmium-containing or cadmium-free. The quantum dot light emitting layer has the characteristics of wide and continuous excitation spectrum distribution, high emission spectrum stability and the like.

In one embodiment, the cathode may be selected from one of an aluminum (Al) electrode, a silver (Ag) electrode, a gold (Au) electrode, and the like, and may also be selected from one of a nano aluminum wire, a nano silver wire, a nano gold wire, and the like.

It should be noted that the quantum dot light emitting diode of the present invention may further include one or more of the following functional layers: a hole injection layer arranged between the hole transport layer and the anode, and an electron injection layer arranged between the electron transport layer and the cathode.

The embodiment of the invention provides a preparation method of a quantum dot light-emitting diode, which comprises the following steps:

preparing a hole transport layer, wherein the material of the hole transport layer comprises the composite material of the embodiment of the invention;

alternatively, an electron transport layer is prepared, the material of which comprises the composite material of the embodiments of the present invention.

The following describes a method for manufacturing a quantum dot light emitting diode in detail, taking the quantum dot light emitting diode with the structure shown in fig. 3 as an example. As shown in fig. 4, the method for manufacturing a quantum dot light emitting diode of this embodiment includes the steps of:

s20, forming a hole transport layer on the anode (formed on the substrate);

s21, forming a quantum dot light-emitting layer on the hole transport layer;

s22, forming an electron transport layer on the quantum dot light-emitting layer;

and S23, forming a cathode on the electron transport layer to obtain the quantum dot light-emitting diode.

In the embodiments of the present invention, the preparation method of the composite material is described above, and is not described herein again.

In step S20, the anode needs to be subjected to a pretreatment process in order to obtain a high-quality hole transport layer. The pretreatment process specifically comprises the following steps: and cleaning the anode with a cleaning agent to primarily remove stains on the surface of the anode, then sequentially and respectively ultrasonically cleaning the anode in deionized water, acetone, absolute ethyl alcohol and deionized water for 20min to remove impurities on the surface, and finally drying the anode by using high-purity nitrogen to obtain the anode.

In one embodiment, the hole transport layer may be formed on the anode using a preparation method not limited thereto, such as drop coating, spin coating, dipping, coating, printing, evaporation, and the like. The preparation method is suitable for the conventional hole transport material and the composite material of the embodiment of the invention.

In one embodiment, step S20 specifically includes: and spin-coating the prepared solution of the hole transport layer material on the anode, and then carrying out thermal annealing treatment at 300-350 ℃ to obtain the hole transport layer. 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.

In one embodiment, step S21 specifically includes: and placing the substrate on which the hole transport layer is coated in a spin coater, coating the prepared solution of the luminescent quantum dots on the hole transport layer in a spin coating manner, and then carrying out thermal annealing treatment to obtain the quantum dot luminescent layer. 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.

In one embodiment, the electron transport layer may be formed on the quantum dot light emitting layer using a preparation method not limited thereto, such as drop coating, spin coating, dipping, coating, printing, and evaporation. The preparation method is suitable for the conventional electron transport materials and is also suitable for the composite material of the embodiment of the invention.

In one embodiment, step S22 specifically includes: and placing the substrate on which the quantum dot light emitting layer is coated in a spin coating machine, coating the prepared solution of the electron transport layer material on the quantum dot light emitting layer in a spin coating mode, and then carrying out thermal annealing treatment at the temperature of 200-300 ℃ to obtain the electron transport layer. The thickness of the film 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. The annealing can be performed in air or in a nitrogen atmosphere, and the annealing atmosphere is selected according to actual needs.

In one embodiment, step S23 specifically includes: and (3) placing the substrate on which the functional layers are deposited in an evaporation bin, and thermally evaporating a layer of cathode material with the thickness of 15-30nm through a mask plate to obtain a cathode. The cathode material can be metallic silver or aluminum, or a nano Ag wire or a Cu wire is used, and the cathode material has smaller resistance so that carriers can be injected smoothly.

In one embodiment, the obtained quantum dot light emitting diode is subjected to an encapsulation process. The packaging process can adopt common machine packaging or manual packaging. Wherein, in the packaging treatment environment, the oxygen content and the water content are both lower than 0.1ppm so as to ensure the stability of the device.

The present invention is further illustrated by the following specific examples.

Example 1

FeN in this example₄The preparation steps of the composite material compounded with ZnO are as follows:

1) first, a suitable amount of zinc acetate was added to 50ml of ethanol to form a solution having a total concentration of 0.5M. Then stirring at 70 deg.C to dissolve, adding alkali solution (molar ratio, OH) prepared by dissolving potassium hydroxide in 10ml ethanol^-：Zn²⁺2: pH 12, 1). Stirring was continued at 70 ℃ for 4h to give a homogeneous, clear solution. Then, after the solution is cooled, ethyl acetate is used for precipitation, a small amount of ethanol is used for dissolution after centrifugation, the precipitation and dissolution steps are repeated for 3 times, and drying is carried out to prepare ZnO nanoparticles;

2) adding appropriate amount of FeCl₃And ammonium chloride were dissolved in 10ml of dimethyl sulfoxide (molar ratio, Fe: N ═ 1:5), and after ultrasonic dissolution, the mixed solution was transferred to a high-pressure high-temperature reaction vessel. Firstly, applying 10GPa high pressure to reaction raw materials, heating to 300 ℃ after the pressure is increased to a preset pressure, preserving heat and pressure for 2 hours, finally cooling under the fixed pressure, and carrying out pressure relief treatment after cooling to room temperature to obtain FeN₄A type semimetal;

3) ZnO nanoparticles and FeN₄The type semimetal was added to 30ml of ethanol to form a solution having a total concentration of 0.5M, wherein ZnO: FeN₄In a molar ratio of 1: 0.5. then stirring and reacting for 2h at 70 ℃, standing, cleaning and drying to prepare FeN₄A composite material compounded with ZnO.

Example 2

MnN in this example₄With TiO₂The preparation steps of the composite material are as follows:

1) first, an appropriate amount of titanium nitrate was added to 50ml of methanol to form a solution having a total concentration of 0.8M. Then dissolved at 60 ℃ with stirring, and a solution of sodium hydroxide dissolved in 10ml of methanol (molar ratio, OH) is added^-：Ti⁴⁺2.5: 1). Stirring was continued at 60 ℃ for 4h to give a homogeneous solution. Then, after the solution is cooled, ethyl acetate is used for precipitation, a small amount of methanol is used for dissolution after centrifugation, the precipitation and dissolution steps are repeated for 3 times, and drying is carried out to obtain TiO₂A nanoparticle;

2) adding proper amount of MnCl₂And urea were dissolved in 10mL of N, N-dimethylformamide (molar ratio, Mn: N ═ 1:6), and after ultrasonic dissolution, the mixed solution was transferred to a high-pressure high-temperature reaction vessel. Firstly, applying 12GPa high pressure to reaction raw materials, heating to 350 ℃ after the pressure is increased to a preset pressure, preserving heat and pressure for 3 hours, finally cooling under the fixed pressure, and performing pressure relief treatment after cooling to room temperature to obtain MnN₄A type semimetal;

3) and mixing the TiO with the solution₂Nanoparticles and MnN₄The type-II semimetal is added to 30ml of ethanol to form a solution with a total concentration of 0.5M, in which TiO is present₂：MnN₄In a molar ratio of 1: 0.3. then stirring and reacting for 2h at 70 ℃, standing, cleaning and drying to obtain MnN₄With TiO₂Composite materials.

Example 3

CoN in this example₄The preparation steps of the composite material compounded with NiO are as follows:

1) first, an appropriate amount of nickel chloride was added to 50ml of propanol to form a solution having a total concentration of 1M. Then stirring at 80 deg.C to dissolve, adding alkaline solution (molar ratio, OH) prepared by dissolving lithium hydroxide in 10ml propanol^-：Ni²⁺2: 1, pH 12). Stirring was continued at 80 ℃ for 4h to give a homogeneous solution. Then, after the solution is cooled, ethyl acetate is used for precipitation, a small amount of ethanol is used for dissolution after centrifugation, the precipitation and dissolution steps are repeated for 3 times, and drying is carried out, so as to prepare NiO nano particles;

2) adding appropriate amount of CoCl₂And dissolving ureaAfter dissolving in 10mL of tetrahydrofuran (molar ratio, Co: N: 1:7) by sonication, the mixed solution was transferred to a high-pressure high-temperature reactor. Firstly, applying 15GPa high pressure to reaction raw materials, heating to 400 ℃ after the pressure is increased to a preset pressure, preserving heat and pressure for 2 hours, finally cooling under the fixed pressure, and carrying out pressure relief treatment after cooling to room temperature to obtain the CoN₄A type semimetal;

3) NiO nanoparticles and CoN₄The type metalloid was added to 30ml ethanol to form a solution with a total concentration of 0.5M, where NiO: CoN₄In a molar ratio of 1: 0.2. then stirring and reacting for 2h at 70 ℃, standing, cleaning and drying to obtain the CoN₄A composite material compounded with NiO.

Example 4

A quantum dot light-emitting diode with a positive structure comprises a laminated structure of an anode and a cathode which are oppositely arranged, a quantum dot light-emitting layer arranged between the anode and the cathode, an electron transport layer arranged between the cathode and the quantum dot light-emitting layer, and a hole transport layer arranged between the anode and the quantum dot light-emitting layer, wherein the anode is arranged on a substrate. The substrate is made of glass sheets, the thickness of the substrate is 2 micrometers, the anode is made of ITO and is 50nm, the hole transport layer is made of TFB and is 40nm, the quantum dot light emitting layer is made of CdZnS/ZnS and is 40nm, and the electron transport layer is made of FeN₄The composite material compounded with ZnO has a thickness of 80nm, and the cathode is made of Al and has a thickness of 80 nm.

The preparation method of the quantum dot light-emitting diode comprises the following steps:

providing an ITO substrate, and preparing a hole transport layer on the ITO substrate;

preparing a quantum dot light emitting layer on the hole transport layer;

depositing the FeN obtained in the method of example 1 on the quantum dot light emitting layer₄Preparing an electron transport layer from a composite material compounded with ZnO;

preparing a cathode on the electron transport layer.

Example 5

This exampleEssentially the same as example 4, except that: the material of the electron transport layer was MnN obtained in the method described in example 2₄With TiO₂Composite materials are provided.

Example 6

This example is substantially the same as example 4, except that: the material of the hole transport layer was CoN obtained in the method described in example 3₄The composite material is compounded with NiO, and the material of the electron transport layer is ZnO.

Example 7

The quantum dot light-emitting diode with the inversion structure comprises a laminated structure of an anode and a cathode which are oppositely arranged, a quantum dot light-emitting layer arranged between the anode and the cathode, an electron transmission layer arranged between the cathode and the quantum dot light-emitting layer, and a hole transmission layer arranged between the anode and the quantum dot light-emitting layer, wherein the cathode is arranged on a substrate. The substrate is made of glass sheets, the thickness of the substrate is 2 micrometers, the cathode is made of ITO and is 50nm, the hole transport layer is made of TFB and is 40nm, the quantum dot light emitting layer is made of CdZnS/ZnS and is 40nm, and the electron transport layer is made of FeN₄The composite material compounded with ZnO has a thickness of 80nm, and the anode is made of Al and has a thickness of 80 nm.

providing an ITO substrate on which FeN obtained in the method described in example 1 is deposited₄Preparing an electron transport layer from a composite material compounded with ZnO;

preparing a quantum dot light-emitting layer on the electron transport layer;

preparing a hole transport layer on the quantum dot light emitting layer;

an anode is prepared on the hole transport layer.

Example 8

This example is substantially the same as example 7 except that: the material of the electron transport layer was MnN obtained by the method described in example 2₄With TiO₂Composite materials.

Example 9

This example is substantially the same as example 7 except that: the material of the hole transport layer was CoN obtained in the method described in example 3₄The composite material is compounded with NiO, and the material of the electron transport layer is ZnO.

Comparative example 1

This comparative example is essentially the same as example 4, except that: the material of the electron transport layer was a commercial ZnO material (available from sigma).

Comparative example 2

This comparative example is essentially the same as example 4, except that: the material of the electron transport layer is commercial TiO₂Material (available from sigma).

Comparative example 3

This comparative example is essentially the same as example 9, except that: the material of the hole transport layer was a commercial NiO material (available from sigma).

The electron transport films prepared in examples 1-2, the hole transport films prepared in example 3, the electron transport films in comparative examples 1-2, the hole transport films in comparative example 3, the quantum dot light emitting diodes prepared in examples 4-9 and comparative examples 1-3 were subjected to performance tests, and the test indexes and the test methods were as follows:

(1) electron mobility: testing the current density (J) -voltage (V) of the electron transport film, drawing a curve relation diagram, fitting the Space Charge Limited Current (SCLC) region in the relation diagram, and then obtaining the current density (J) -voltage (V) of the electron transport film according to the well-known Child^,The electron mobility is calculated by the formula slaw:

J＝(9/8)ε_rε₀μ_eV²/d³

wherein J represents current density in mAcm^-2；ε_rDenotes the relative dielectric constant,. epsilon₀Represents the vacuum dielectric constant; mu.s_eRepresents the electron mobility in cm²V^-1s^-1(ii) a V represents a driving voltage and has a unit of V; d represents the film thickness in m.

(2) Hole mobility: testing the current density (J) -voltage (V) of the hole transport film, drawing a curve relation graph, fitting a Space Charge Limited Current (SCLC) region in the relation graph, and then calculating the hole mobility according to a well-known Child's law formula:

J＝(9/8)ε_rε₀μ_eV²/d³

wherein J represents current density in mAcm^-2；ε_rDenotes the relative dielectric constant,. epsilon₀Represents the vacuum dielectric constant; mu.s_eDenotes hole mobility in cm²V^-1s^-1(ii) a V represents a driving voltage in units of V; d represents the film thickness in m.

(3) Resistivity: the resistivity of the electron transport film is measured by the same resistivity measuring instrument.

(4) External Quantum Efficiency (EQE): measured using an EQE optical test instrument.

Note: the electron mobility, hole mobility and resistivity were tested as single layer thin film structure devices, i.e.: cathode/electron (hole) transport film/anode. The external quantum efficiency test is the QLED device, namely: anode/hole transport film/quantum dot light emitting layer/electron transport film/cathode, or cathode/electron transport film/quantum dot light emitting layer/hole transport film/anode.

The test results are shown in table 1 below:

TABLE 1

As can be seen from Table 1 above, examples 1 to 3 of the present invention provide MN as a material₄The electron transport film (hole transport film) of the composite material compounded with the metal oxide had a resistivity significantly lower than that of the electron transport film (hole transport film) made of the metal oxide composite material in comparative examples 1 to 3, and the electron mobility (hole mobility) was significantly higher than that of the electron transport film (hole transport film) made of the metal oxide composite material in comparative examples 1 to 3.

Quantum dot light emitting diodes (MN) provided in embodiments 4 to 9 of the present invention₄Composite material of type semimetal and metal oxide) is obviously higher than that of the quantum dot light-emitting diode of the metal oxide composite material in the comparative examples 1 to 3, which shows that the quantum dot light-emitting diode obtained in the examples has better luminous efficiency.

It is noted that the embodiments provided by the present invention all use blue light quantum dots Cd_XZn_1-XS/ZnS is used as a material of a luminescent layer, is based on a blue light luminescent system, is a system which uses more blue light quantum dots (the blue light quantum dots have more reference values because the high efficiency of the light emitting diode is difficult to achieve), and does not represent that the invention is only used for the blue light luminescent system.

It is to be understood that the invention is not limited to the examples described above, but that modifications and variations may be effected thereto by those of ordinary skill in the art in light of the foregoing description, and that all such modifications and variations are intended to be within the scope of the invention as defined by the appended claims.

Claims

1. A composite material comprising metal oxide nanoparticles and MN₄Type semimetal, metal oxide nanoparticles and MN₄Type of semimetal binding, in which MN₄M in the type semimetal is a metal atom with an outermost layer of a 3d electron orbit.

2. The composite material of claim 1, wherein the metal oxide nanoparticles have hydroxyl ligands bound to the surface thereof, and the hydroxyl ligands on the surface of the metal oxide nanoparticles are bound to MN₄And (3) coordinating and combining metal elements on the surface of the semi-metal.

3. The composite of claim 1, wherein MN is present₄The type semimetal is selected from FeN₄Type semimetal, CoN₄Type semimetal, MnN₄Type semimetal and AlN₄One or more of type semi-metals.

4. The composite material according to claim 1, wherein the metal oxide nanoparticles are metal oxide nanoparticles used as an electron transport material; alternatively, the metal oxide nanoparticles are metal oxide nanoparticles used as a hole transport material.

5. Composite material according to claim 4, characterized in that the metal oxide nanoparticles used as electron transport material are selected from ZnO nanoparticles, TiO nanoparticles₂Nanoparticles, SnO₂One or more of nanoparticles;

6. The composite material of claim 1, wherein the metal oxide nanoparticles are bound to MN₄The molar ratio of the type-II semimetal is 1: (0.2-0.5).

7. A method for preparing a composite material according to any one of claims 1 to 6, comprising the steps of:

8. The method for preparing the composite material according to claim 7, wherein the reaction temperature is 60-80 ℃ and/or the reaction time is 2-4 h.

9. A quantum dot light-emitting diode comprising a hole transport layer comprising the composite material according to any one of claims 1 to 6;

alternatively, an electron transport layer comprising the composite material of any one of claims 1 to 6 is included.

10. A preparation method of a quantum dot light-emitting diode is characterized by comprising the following steps:

preparing a hole transport layer, wherein the material of the hole transport layer comprises the composite material of any one of claims 1 to 6;

alternatively, an electron transport layer is prepared, the material of the electron transport layer comprising the composite material according to any one of claims 1 to 6.