CN112397655A

CN112397655A - Composite material, preparation method thereof and quantum dot light-emitting diode

Info

Publication number: CN112397655A
Application number: CN201910762596.1A
Authority: CN
Inventors: 何斯纳; 吴龙佳; 吴劲衡
Original assignee: TCL Research America Inc
Current assignee: TCL Research America Inc
Priority date: 2019-08-19
Filing date: 2019-08-19
Publication date: 2021-02-23
Anticipated expiration: 2039-08-19
Also published as: CN112397655B

Abstract

The invention belongs to the technical field of nano materials, and particularly relates to a composite material, a preparation method thereof and a quantum dot light-emitting diode. The composite material comprises nickel oxide nano particles and copper ethylene diamine tetraacetate bonded on the surfaces of the nickel oxide nano particles; wherein, the copper ions in the copper ethylenediaminetetraacetate are combined with the oxygen ions on the surface of the nickel oxide nano-particles. The copper ethylene diamine tetraacetate in the composite material can not only improve the dispersibility of the nickel oxide nanoparticles and prevent the nickel oxide nanoparticles from agglomerating, but also improve the conductivity of the nickel oxide nanoparticles, and can improve the work function of the nickel oxide, so that the injection capability of the hole of the nickel oxide nanoparticles is improved.

Description

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

Technical Field

The invention belongs to the technical field of nano materials, and particularly relates to a composite material, a preparation method thereof and a quantum dot light-emitting diode.

Background

The Quantum Dots (QDs) of the semiconductor have Quantum size effect, people can realize the required luminescence with specific wavelength by regulating and controlling the size of the QDs, 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. Conduction band electrons in wide bandgap semiconductors can be accelerated under high electric fields to obtain high enough energy to strike QDs to cause it to emit light.

Nickel oxide (NiO) is used as a p-type semiconductor material, has adjustable band gaps (the band gap is 3.6eV-4.0eV, the HOMO energy level is-5.4 eV-5.0 eV, and the LUMO energy level is-1.6 eV), has higher light transmission performance in an ultraviolet light region, a visible light region and a near infrared light region, and has the advantages of excellent chemical stability, unique light, electricity and magnetic properties and the like, and can be widely applied to electrochromic devices, organic light emitting diodes, gas sensors, dye-sensitized solar cells and p-n heterojunctions. But NiO is less conductive than other materials.

Therefore, the prior art is in need of improvement.

Disclosure of Invention

The invention aims to provide a composite material, a preparation method thereof and a quantum dot light-emitting diode, and aims to solve the technical problem of poor conductivity of the existing nickel oxide.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention provides a composite material, which comprises nickel oxide nano particles and copper ethylene diamine tetraacetate combined on the surfaces of the nickel oxide nano particles; wherein, the copper ions in the copper ethylenediaminetetraacetate are combined with the oxygen ions on the surface of the nickel oxide nano-particles.

The composite material provided by the invention comprises nickel oxide nanoparticles and copper ethylenediaminetetraacetate combined on the surfaces of the nickel oxide nanoparticles, organic groups in the copper ethylenediaminetetraacetate can be dissolved in an organic solvent on one hand, so that the dispersibility of the nickel oxide nanoparticles can be improved, the nickel oxide nanoparticles are prevented from agglomerating, and on the other hand, the composite material has certain electron donating capacity and can improve the electron donating capacityConductivity of high nickel oxide; metallic Cu²⁺NiO crystal lattice is easy to introduce to fill Ni vacancy, so that the surface defect of nickel oxide nano-particle is reduced, the positions of valence band top and conduction band bottom of NiO can be calculated by the density functional theory and are respectively determined by O2 p orbit and Ni 3d orbit, and Cu²⁺Due to its reaction with Ni²⁺The molecular orbitals are induced to be rearranged after the NiO crystal lattice is entered, so that the work function of NiO is improved, the injection capability of the hole of the NiO is improved, the NiO crystal lattice is used for a hole transmission layer of a quantum dot light-emitting diode, the effective combination of electrons and holes can be promoted, the influence of exciton accumulation on the performance of the device is reduced, and the performance of the device is improved.

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

preparing a nickel oxide nanoparticle solution and an ethylene diamine tetraacetic acid copper solution;

mixing the nickel oxide nanoparticle solution and the ethylenediaminetetraacetic acid copper solution, and heating to obtain a precursor solution;

and carrying out solid-liquid separation on the precursor solution to obtain the composite material.

The preparation method of the composite material provided by the invention directly mixes the prepared nickel oxide nanoparticle solution and the ethylenediaminetetraacetic acid copper solution, then carries out heating treatment, and then carries out solid-liquid separation to obtain the composite material.

Finally, the invention also provides a quantum dot light-emitting diode which comprises an anode, a cathode and a quantum dot light-emitting layer positioned between the anode and the cathode, wherein a hole transport layer is arranged between the anode and the quantum dot light-emitting layer, and the hole transport layer is composed of the composite material or the composite material prepared by the preparation method.

The hole transport layer in the quantum dot light-emitting diode provided by the invention is composed of the special composite material or the special composite material prepared by the preparation method provided by the invention, and the composite material can promote the effective recombination of electrons and holes and reduce the influence of exciton accumulation on the performance of the device, thereby improving the luminous efficiency and the display performance of the device.

Drawings

FIG. 1 is a schematic structural diagram of a composite material provided by the present invention; wherein a is nickel oxide nano-particles, b is copper ethylenediamine tetraacetate, L is ethylenediamine tetraacetic acid, and M is copper;

FIG. 2 is a schematic diagram of the chemical structure of EDTA-Cu in the composite material provided by the present invention; wherein M is copper;

FIG. 3 is a schematic flow chart of a method for preparing the composite material provided by the present invention;

FIG. 4 is a schematic structural diagram of an LED with positive quantum dots according to the present invention

Fig. 5 is a schematic structural diagram of an inverted quantum dot light emitting diode provided by the present invention.

Detailed Description

In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

In one aspect, an embodiment of the present invention provides a composite material, as shown in fig. 1, including nickel oxide nanoparticles a and copper ethylenediaminetetraacetate b bonded to surfaces of the nickel oxide nanoparticles a; wherein, the copper ions M in the copper ethylenediaminetetraacetate b are combined with oxygen ions (not labeled in the figure) on the surface of the nickel oxide nanoparticles a.

Ethylenediaminetetraacetic acid (EDTA) of formula C₁₀H₁₆N₂O₈It is a common chelating agent capable of binding to metal ions. The EDTA and copper form EDTA-Cu metal complex with chemical structure shown in FIG. 2, and the EDTA molecule has two nitrogen atoms andfour carboxyl hydroxyl oxygen atoms are combined with copper ions to form a hexadentate chelate, and M is copper ions. Due to Cu²⁺Radius (0.074nm) and Ni²⁺Radii (0.069nm) are similar, so that metallic Cu²⁺NiO crystal lattices are easy to introduce, Ni vacancies are filled, and the surface defects of nickel oxide nano particles are reduced; with Cu²⁺O capable of being bonded with NiO surface²⁺And (4) combining to form the EDTA-Cu-NiO nano material. EDTA-Cu contains organic groups and metal ions, has both organic and inorganic properties, and has larger modulation space than single organic or inorganic modification.

The composite material provided by the embodiment of the invention comprises nickel oxide nanoparticles and copper ethylenediaminetetraacetate bonded on the surfaces of the nickel oxide nanoparticles, wherein organic groups in the copper ethylenediaminetetraacetate can be dissolved in an organic solvent, so that the dispersibility of the nickel oxide nanoparticles can be improved, the nickel oxide nanoparticles are prevented from agglomerating, and the composite material has a certain electron supply capacity and can improve the conductivity of the nickel oxide; the positions of the valence band top and the conduction band bottom of NiO can be calculated by the density functional theory and are respectively determined by an O2 p orbit and an Ni 3d orbit, and Cu²⁺Due to its reaction with Ni²⁺The electronegativity of the quantum dot light-emitting diode is different, the molecular orbitals are induced to be rearranged after the NiO crystal lattice is entered, the work function of NiO is improved, and therefore the hole injection capability of the NiO crystal lattice is improved.

The composite material provided by the embodiment of the invention is used as a hole transport material of a quantum dot light-emitting diode.

In one embodiment, in the composite material, the molar ratio of nickel oxide to copper ethylenediaminetetraacetate in the nickel oxide nanoparticles is 1: (0.05-0.15). If the amount of EDTA-Cu is insufficient, the EDTA-Cu can not be fully matched with the surface of the nickel oxide nano-particles, the modification effect on the nickel oxide is small, and the performance of the device can not be well improved; if the amount of EDTA-Cu is too large, too much nickel oxide of EDTA-Cu is incorporated, which affects the hole transport efficiency. Optimally, the molar ratio of nickel oxide to EDTA-Cu is maintained at 1: (0.05 to 0.15), a hole transporting material having the best performance can be obtained.

Accordingly, another aspect of the embodiments of the present invention provides a method for preparing a composite material, as shown in fig. 3, the method comprising the following steps:

s01: preparing a nickel oxide nanoparticle solution and an ethylene diamine tetraacetic acid copper solution;

s02: mixing the nickel oxide nanoparticle solution and the ethylenediaminetetraacetic acid copper solution, and heating to obtain a precursor solution;

s03: and carrying out solid-liquid separation on the precursor solution to obtain the composite material.

The preparation method of the composite material provided by the invention is a simple sol-gel method, the prepared nickel oxide nanoparticle solution and the ethylene diamine tetraacetic acid copper solution are directly mixed and then are subjected to heating treatment, then the composite material can be obtained through solid-liquid separation, the preparation method has the characteristics of simple process and low cost, and is suitable for large-area and large-scale preparation.

In the above step S01: the solution of copper ethylenediaminetetraacetate can be prepared by the following method: adding EDTA and copper oxide into water, reacting, drying to obtain copper ethylenediamine tetraacetate, and dissolving the copper ethylenediamine tetraacetate in an organic solvent to obtain a copper ethylenediamine tetraacetate solution. In the above process, when the molar ratio of EDTA to copper ions is less than 1:1, EDTA is not sufficient with Cu²⁺Carrying out compounding to form a metal organic compound; when the mole ratio of EDTA to copper ions is more than 1.2:1, excess EDTA was not easily removed in subsequent reactions. Thus, optimally, the molar ratio, EDTA: cu²⁺1-1.2: 1. EDTA forms a hexadentate chelate by the bonding of two nitrogen atoms and four carboxyoxyhydroxy oxygen atoms in the molecule with copper ions.

The nickel oxide nanoparticle solution may be prepared by the following method: dissolving nickel salt in an organic solvent to obtain a nickel salt solution; then adding alkali liquor into the nickel salt solution, heating and stirring to obtain the nickel oxide nano-particle solution.

Wherein the nickel salt is soluble inorganic nickel salt or organic nickel salt, such as nickel acetate, nickel nitrate, nickel chloride, nickel sulfate, nickel acetate tetrahydrate, etc., but not limited thereto. The organic solvent is not limited thereto, and is ethylene glycol, isopropyl alcohol, methanol, ethanol, propanol, butanol, or the like. The alkali solution is not limited to sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonia water, ethanolamine, diethanolamine, triethanolamine, ethylenediamine, tetramethylammonium hydroxide, and other alkali solutions. The concentration of the nickel salt solution is 0.2M (mol/L) -1M; the molar ratio of the alkali liquor to be added is satisfied, and the ratio of hydroxide ions: ni²⁺(1.8-2.5): 1, pH 12-13. The heating and stirring temperature is 60-90 ℃; stirring for 4-6 h.

In the embodiment of the invention, organic alkali and/or inorganic alkali is/are dropwise added into a nickel salt solution, the mixture is stirred and dissolved at a constant temperature, and the nickel salt solution reacts under an alkaline condition to obtain a NiO crystal solution. Wherein the molar ratio of hydroxide ions to nickel ions of the organic base and/or the inorganic base is (1.8-2.5): 1, when the ratio of hydroxide ions to nickel ions is less than 1.8: 1, excessive metal salt, wherein the added nickel ions can not completely react; greater than 2.5: 1, too high a pH results in a slower polycondensation rate in the system. Optimally, the ratio of the molar amount of hydroxide ions to the molar amount of nickel ions is maintained at (1.8-2.5): 1, nickel oxide nanoparticles with uniform particle distribution can be obtained.

In the above step S02: and mixing the nickel oxide nanoparticle solution and the ethylenediaminetetraacetic acid copper solution, and combining copper ions in ethylenediaminetetraacetic acid copper and oxygen ions on the surface of the nickel oxide nanoparticles in the heating process to form the EDTA-Cu-NiO nano material. Preferably, the temperature for the heat treatment is 60-90 ℃; the time of the heat treatment is 2-4 h. Under the condition, the nickel oxide nano-crystal modified by the copper ethylenediamine tetraacetate can be better formed in the precursor solution. Further, in the step of mixing the nickel oxide nanoparticle solution and the copper ethylenediaminetetraacetate solution, the molar ratio of nickel oxide in the nickel oxide nanoparticle solution to copper ethylenediaminetetraacetate in the copper ethylenediaminetetraacetate solution is 1: (0.05-0.15). When the amount of EDTA-Cu is insufficient, the EDTA-Cu can not be sufficiently matched with the surface of the nickel oxide; when EDTA-Cu is too much, the hole transport efficiency is affected. Optimally, when the molar ratio of the nickel oxide to the EDTA-Cu is kept to be 1 (0.05-0.15), a hole transport material with better performance can be obtained.

Further, the step of mixing the nickel oxide nanoparticle solution and the ethylenediaminetetraacetic acid copper solution comprises: and dropwise adding the copper ethylenediamine tetraacetate solution into the nickel oxide nanoparticle solution. The two solutions are mixed more fully in a dropwise manner. Further, the solvent in the nickel oxide nanoparticle solution and the solvent in the copper ethylenediaminetetraacetate solution are the same organic solvent. The solvent in the nickel oxide nanoparticle solution is the same as that in the copper ethylenediaminetetraacetate solution, so that the solubility of the two solutions is not affected after the two solutions are mixed. Specifically, the organic solvent is not limited thereto, but ethylene glycol, isopropyl alcohol, methanol, ethanol, propanol, butanol, or the like.

In the above step S03: and the step of carrying out solid-liquid separation on the precursor solution comprises a sedimentation treatment or an annealing treatment. For the sedimentation treatment, the precursor solution can be cooled to room temperature (the room temperature of the embodiment of the invention is 10-35 ℃), then the sedimentation treatment is carried out to separate out the nickel oxide nanocrystal modified by the copper ethylenediaminetetraacetate in the precursor solution, and the sediment is collected, cleaned and dried to obtain the composite material. The settling treatment is realized by adding a precipitating agent, and the precipitating agent is a non-polar solvent, such as heptane, octane and the like. For the annealing treatment, the precursor solution can be directly annealed at the temperature of 100-150 ℃ to obtain the powdery nickel oxide nano material modified by the EDTA copper. In a specific embodiment, in order to obtain the composite material film, a precursor solution can be deposited on a substrate for annealing treatment, so that the nickel oxide nano material film modified by copper ethylenediaminetetraacetate is obtained; specifically, the temperature of the annealing treatment is 100-150 ℃; the time of the annealing treatment is 10-20 min. The annealing condition can remove the solvent better and anneal to form a film.

Finally, an embodiment of the present invention further provides a quantum dot light emitting diode, including an anode, a cathode, and a quantum dot light emitting layer located between the anode and the cathode, where a hole transport layer is disposed between the anode and the quantum dot light emitting layer, and the hole transport layer is composed of the composite material described above in the embodiment of the present invention or the composite material prepared by the preparation method described above in the embodiment of the present invention.

The hole transport layer in the quantum dot light-emitting diode provided by the embodiment of the invention is composed of the special composite material or the special composite material prepared by the preparation method provided by the embodiment of the invention, and the composite material can promote effective electron-hole recombination, reduce the influence of exciton accumulation on the performance of the device, and further improve the luminous efficiency and the display performance of the device.

In one embodiment, a hole injection layer is further disposed between the hole transport layer and the anode. In another embodiment, an electron functional layer, such as an electron transport layer, or a stack of an electron injection layer and an electron transport layer, is disposed between the quantum dot light emitting layer and the cathode, wherein the electron injection layer is adjacent to the cathode.

In one embodiment, a method for manufacturing a QLED device includes the steps of:

a: firstly, growing a hole transport layer on a substrate; the material of the hole transport layer is the nickel oxide nanoparticle material with the surface modified by EDTA-Cu.

B: then depositing a quantum dot light-emitting layer on the hole transport layer;

c: and finally, depositing an electron transmission layer on the quantum dot light-emitting layer, and evaporating a cathode on the electron transmission layer to obtain the quantum dot light-emitting diode.

In order to obtain a high-quality hole transport layer, the ITO substrate needs to be subjected to a pretreatment process. The specific processing steps of the substrate include: cleaning the whole piece of ITO conductive glass with a cleaning agent to primarily remove stains on the surface, then sequentially carrying out ultrasonic cleaning in deionized water, acetone, absolute ethyl alcohol and deionized water for 20min respectively to remove impurities on the surface, and finally blowing dry with high-purity nitrogen to obtain the ITO anode.

The hole transport layer is made of EDTA-Cu modified NiO nano-particle material. The preparation method of the hole transport layer is a spin coating process, and includes but is not limited to drop coating, spin coating, soaking, coating, printing, evaporation and the like. Hole transport layer: spin coating the solution of the prepared hole transport layer material to form a film; the film thickness is controlled by adjusting the concentration of the solution, the spin coating speed and the spin coating time, and then the thermal annealing treatment is carried out at the temperature of 100-150 ℃, so that the thickness of the hole transport layer is 20-60 nm.

The quantum dots in the quantum dot light-emitting layer are oil-soluble quantum dots and comprise binary phase, ternary phase and quaternary phase quantum dots; wherein the binary phase quantum dots include CdS, CdSe, CdTe, InP, AgS, PbS, PbSe, HgS, etc., but are not limited thereto, and the ternary phase quantum dots include Zn_XCd_1-XS、Cu_XIn_1-XS、Zn_XCd_1-XSe、Zn_XSe_1-XS、Zn_XCd_1-XTe、PbSe_XS_1-XEtc. are not limited thereto, and the quaternary phase quantum dots include, Zn_XCd_1-XS/ZnSe、Cu_XIn_1-XS/ZnS、Zn_XCd_1-XSe/ZnS、CuInSeS、Zn_XCd_1-XTe/ZnS、PbSe_XS_1-Xthe/ZnS and the like are not limited thereto. Then the quantum dots can be any one of the three common red, green and blue quantum dots or other yellow light, and the quantum dots can be cadmium-containing or cadmium-free. The quantum dot light emitting layer of the material has the characteristics of wide and continuous excitation spectrum distribution, high emission spectrum stability and the like. Preparing a quantum dot light-emitting layer: spin-coating the prepared luminescent material solution with a certain concentration on a spin coater of a substrate with a spin-coated hole transport layer to form a film, controlling the thickness of the luminescent layer to be about 20-60nm by adjusting the concentration of the solution, the spin-coating speed and the spin-coating time, and drying at a proper temperature.

The electron transport layer can be made of electron transport materials conventional in the art, including but not limited to ZnO, TiO₂、CsF、LiF、CsCO₃And Alq₃One kind of (1). Preparation of an electron transport layer: placing the substrate with the luminous layer in a vacuum evaporation chamber, evaporating an electron transmission layer with the thickness of about 80nm at the evaporation speed of about 0.01-0.5 nm/s, and annealing at a proper temperature.

And then, the substrate deposited with the functional layers is placed in an evaporation bin, and a layer of 15-30nm metal silver or aluminum is thermally evaporated through a mask plate to serve as a cathode, or a nano Ag wire or a Cu wire is used, so that a carrier can be smoothly injected due to the small resistance.

Further, the obtained QLED is subjected to a packaging process, and the packaging process may be performed by a common machine or by a manual method. Preferably, the oxygen content and the water content in the packaging treatment environment are both lower than 0.1ppm so as to ensure the stability of the device.

The invention is described in further detail with reference to a part of the test results, which are described in detail below with reference to specific examples.

Example 1

The preparation process of the composite material film is described in detail by taking copper oxide, EDTA, nickel chloride, ethanol and sodium hydroxide as examples.

(1) Placing 1g EDTA in a small beaker, adding 10ml distilled water, stirring at 80 deg.C for dissolving, and slowly adding appropriate amount of copper oxide (molar ratio, EDTA: Cu) under magnetic stirring²⁺1:1), reacting for 2h to obtain an EDTA-Cu solution, and drying the EDTA-Cu solution in an oven to obtain EDTA-Cu powder.

(2) Adding a proper amount of nickel chloride into 50ml of ethanol, and stirring and dissolving at 70 ℃ to form a salt solution with the total concentration of 1M. Weighing sodium hydroxide, and dissolving in 10ml ethanol solution to obtain alkali liquor; according to OH^-And the molar ratio of nickel ions is 2:1, adding alkali liquor into the salt solution to form a mixed solution with the pH value of 12, and stirring for 4h at 70 ℃ to obtain a NiO nano-particle solution.

(3) Dissolving a proper amount of EDTA-Cu powder in ethanol to obtain an EDTA-Cu solution, slowly and dropwisely adding the EDTA-Cu solution into a NiO nano-particle solution reaction system, and stirring for 3 hours at 70 ℃ to form a precursor solution (molar ratio, nickel oxide: EDTA-Cu is 1: 0.1);

(4) and then, after the solution is cooled, spin-coating the treated ITO by using a spin coater and annealing at 150 ℃ to obtain a composite material film, namely the ethylene diamine tetraacetic acid copper modified nickel oxide nano material film.

Example 2

(1) Placing 1g EDTA in a small beaker, adding 10ml distilled water, stirring at 80 deg.C for dissolving, and slowly adding appropriate amount of copper oxide (molar ratio, EDTA: Cu) under magnetic stirring²⁺1.2:1), reacting for 2h to obtain an EDTA-Cu solution, and drying the EDTA-Cu solution in an oven to obtain EDTA-Cu powder.

(3) Dissolving a proper amount of EDTA-Cu powder in ethanol to obtain an EDTA-Cu solution, slowly and dropwisely adding the EDTA-Cu solution into a NiO nano-particle solution reaction system, and stirring for 3 hours at 70 ℃ to form a precursor solution (molar ratio, nickel oxide: EDTA-Cu is 1: 0.05);

Example 3

The preparation process of the composite material film is described in detail by taking copper oxide, EDTA, nickel nitrate, methanol and potassium hydroxide as examples.

(2) An appropriate amount of nickel nitrate was added to 50ml of methanol, and dissolved at 60 ℃ with stirring to form a salt solution having a total concentration of 1M. Weighing potassium hydroxideDissolving in 10ml of methanol solution to obtain alkali liquor; according to OH^-And the molar ratio of nickel ions is 2:1, adding alkali liquor into the salt solution to form a mixed solution with the pH value of 12, and stirring for 4h at the temperature of 60 ℃ to obtain a NiO nano-particle solution.

(3) Dissolving a proper amount of EDTA-Cu powder in methanol to obtain an EDTA-Cu solution, slowly and dropwisely adding the EDTA-Cu solution into a NiO nano-particle solution reaction system, and stirring for 3 hours at the temperature of 60 ℃ to form a precursor solution (the molar ratio of nickel oxide to EDTA-Cu is 1: 0.1);

Example 4

(2) An appropriate amount of nickel nitrate was added to 50ml of methanol, and dissolved at 60 ℃ with stirring to form a salt solution having a total concentration of 1M. Weighing potassium hydroxide, and dissolving in 10ml of methanol solution to obtain alkali liquor; according to OH^-And the molar ratio of nickel ions is 2:1, adding alkali liquor into the salt solution to form a mixed solution with the pH value of 12, and stirring for 4h at the temperature of 60 ℃ to obtain a NiO nano-particle solution.

(3) Dissolving a proper amount of EDTA-Cu powder in methanol to obtain an EDTA-Cu solution, slowly and dropwisely adding the EDTA-Cu solution into a NiO nano-particle solution reaction system, and stirring for 3 hours at the temperature of 60 ℃ to form a precursor solution (the molar ratio of nickel oxide to EDTA-Cu is 1: 0.15);

Example 5

The preparation process of the composite material film is described in detail by taking copper oxide, EDTA, nickel sulfate, propanol and ethanolamine as examples.

(1) Adding 1g EDTA into a small beaker, adding 10ml distilled water, stirring at 80 deg.C for dissolving, and slowly adding appropriate amount of copper oxide (molar ratio, EDTA: Cu) under magnetic stirring²⁺1:1), reacting for 2h to obtain an EDTA-Cu solution, and drying the EDTA-Cu solution in an oven to obtain EDTA-Cu powder.

(2) The appropriate amount of nickel sulfate was added to 50ml of propanol and dissolved at 80 ℃ with stirring to form a salt solution with a total concentration of 1M. Weighing ethanolamine, and dissolving the ethanolamine in 10ml of propanol solution to obtain alkali liquor; according to OH^-And the molar ratio of nickel ions is 2:1, adding alkali liquor into the salt solution to form a mixed solution with the pH value of 12, and stirring for 4h at 80 ℃ to obtain a NiO nano-particle solution.

(3) Dissolving a proper amount of EDTA-Cu powder in propanol to obtain an EDTA-Cu solution, slowly and dropwisely adding the EDTA-Cu solution into a NiO nano-particle solution reaction system, and stirring for 3 hours at 80 ℃ to form a precursor solution (molar ratio, nickel oxide: EDTA-Cu is 1: 0.1);

Example 6

A QLED device is prepared by the following steps:

a: firstly, growing a hole transport layer on a substrate; the hole transport layer was prepared as described in example 1;

c: depositing an electron transport layer on the quantum dot light emitting layer;

d: and finally, evaporating a cathode on the electron transmission layer to obtain the quantum dot light-emitting diode.

The QLED device of the present embodiment is in an upright configuration, and has a structure as shown in fig. 4, and includes, in order from bottom to top, 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. The substrate 1 is made of a glass sheet, the anode 2 is made of an ITO substrate, the hole transport layer 3 is made of the EDTA-Cu modified NiO nanomaterial prepared in the embodiment 1, the electron transport layer 5 is made of ZnO, and the cathode 6 is made of Al.

Example 7

A QLED device is prepared by the following steps:

a: firstly, growing a hole transport layer on a substrate; the hole transport layer was prepared as described in example 2;

The QLED device of the present embodiment is in an upright configuration, and has a structure as shown in fig. 4, and includes, in order from bottom to top, 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. The substrate 1 is made of a glass sheet, the anode 2 is made of an ITO substrate, the hole transport layer 3 is made of the EDTA-Cu modified NiO nanomaterial prepared in the embodiment 2, the electron transport layer 5 is made of ZnO, and the cathode 6 is made of Al.

Example 8

A QLED device is prepared by the following steps:

a: firstly, growing a hole transport layer on a substrate; the hole transport layer was prepared as described in example 3;

The QLED device of the present embodiment is in an upright configuration, and has a structure as shown in fig. 4, and includes, in order from bottom to top, 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. The substrate 1 is made of a glass sheet, the anode 2 is made of an ITO substrate, the hole transport layer 3 is made of the EDTA-Cu modified NiO nanomaterial prepared in example 3, the electron transport layer 5 is made of ZnO, and the cathode 6 is made of Al.

Example 9

A QLED device is prepared by the following steps:

a: firstly, growing an electron transmission layer on a substrate;

b: then depositing a quantum dot light-emitting layer on the electron transport layer;

c: depositing a hole transport layer on the quantum dot light emitting layer; the hole transport layer was prepared as described in example 4;

d: and finally, evaporating an anode on the hole transport layer to obtain the quantum dot light-emitting diode.

The QLED device of the present embodiment has an inverted configuration, and its structure is shown in fig. 5, and the QLED device includes, in order from bottom to top, a substrate 1, a cathode 6, an electron transport layer 5, a quantum dot light-emitting layer 4, a hole transport layer 3, and an anode 2. The substrate 1 is made of a glass sheet, the cathode 6 is made of an ITO substrate, the hole transport layer 3 is made of the EDTA-Cu modified NiO nanomaterial prepared in example 4, the electron transport layer 5 is made of ZnO, and the anode 2 is made of Al.

Example 10

A QLED device is prepared by the following steps:

a: firstly, growing an electron transmission layer on a substrate;

c: depositing a hole transport layer on the quantum dot light emitting layer; the hole transport layer was prepared as described in example 5;

The QLED device of the present embodiment has an inverted configuration, and its structure is shown in fig. 5, and the QLED device includes, in order from bottom to top, a substrate 1, a cathode 6, an electron transport layer 5, a quantum dot light-emitting layer 4, a hole transport layer 3, and an anode 2. The substrate 1 is made of a glass sheet, the cathode 6 is made of an ITO substrate, the hole transport layer 3 is made of the EDTA-Cu modified NiO nanomaterial prepared in example 5, the electron transport layer 5 is made of ZnO, and the anode 2 is made of Al.

Comparative example 1

A quantum dot light-emitting diode 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 a glass sheet, the anode is made of an ITO substrate, the hole transport layer is made of a commercial nickel oxide material (purchased from Sigma company), the electron transport layer is made of a ZnO nano material, and the cathode is made of Al.

Comparative example 2

A quantum dot light-emitting diode 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 anode is made of an ITO substrate, the hole transport layer is made of an unmodified nickel oxide nano material, the electron transport layer is made of a ZnO nano material, and the cathode is made of Al.

And (3) performance testing:

the EDTA-Cu modified NiO nano-material hole transport films prepared in the examples 1 to 5, the hole transport layers in the comparative examples 1 and 2, the quantum dot light-emitting diodes prepared in the examples 6 to 10 and the comparative examples 1 and 2 were subjected to performance tests, and the test indexes and the test methods are as follows:

(1) 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 the drive voltage, in units of V; d represents the film thickness in m.

(2) Resistivity: and measuring the resistivity of the hole transport film by using the same resistivity measuring instrument.

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

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

The test results are shown in table 1 below:

TABLE 1

As can be seen from the data in table 1 above, the resistivity of the hole transport film of the edta-modified nickel oxide nanomaterial provided in examples 1-5 of the present invention is significantly lower than that of the hole transport films in comparative examples 1 and 2, and the hole mobility is significantly higher than that of the hole transport films prepared in comparative examples 1 and 2.

The external quantum efficiency of the quantum dot light-emitting diode (the hole transport layer is made of the nickel oxide nanomaterial modified by copper ethylenediaminetetraacetate) provided by the embodiments 6 to 10 of the invention is obviously higher than that of the quantum dot light-emitting diode in the comparative examples 1 and 2, which shows that the quantum dot light-emitting diode obtained by the embodiments of the invention 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 that a blue light luminescent system uses more systems (the blue light quantum dot luminescent diode has more reference value because high efficiency is difficult to achieve), and does not represent that the invention is only used for the blue light luminescent system.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims

1. A composite material, comprising nickel oxide nanoparticles and copper ethylenediaminetetraacetate bonded to the surface of the nickel oxide nanoparticles; wherein copper ions in the copper ethylenediaminetetraacetate are combined with oxygen ions on the surface of the nickel oxide nano-particles.

2. The composite material of claim 1, wherein the nickel oxide nanoparticles have a molar ratio of nickel oxide to copper ethylenediaminetetraacetate of 1: (0.05-0.15).

3. The composite material of claim 1, wherein the composite material is used as a hole transport material for a quantum dot light emitting diode.

4. The preparation method of the composite material is characterized by comprising the following steps:

5. The method for preparing a composite material according to claim 4, wherein the temperature of the heat treatment is 60 to 90 ℃; and/or the presence of a gas in the gas,

the time of the heat treatment is 2-4 h.

6. The method of claim 4, wherein the subjecting the precursor solution to solid-liquid separation comprises a sedimentation treatment or an annealing treatment.

7. The method of claim 4, wherein in the step of mixing the nickel oxide nanoparticle solution with the copper ethylenediaminetetraacetate solution, the molar ratio of nickel oxide in the nickel oxide nanoparticle solution to copper ethylenediaminetetraacetate in the copper ethylenediaminetetraacetate solution is 1: (0.05-0.15).

8. The method of claim 4, wherein the solvent in the nickel oxide nanoparticle solution and the solvent in the copper ethylenediaminetetraacetate solution are the same organic solvent.

9. The method of preparing a composite material according to claim 8, wherein the organic solvent is at least one selected from the group consisting of methanol, ethanol, propanol, butanol, and ethylene glycol.

10. A quantum dot light-emitting diode comprising an anode, a cathode and a quantum dot light-emitting layer between the anode and the cathode, wherein a hole transport layer is arranged between the anode and the quantum dot light-emitting layer, and the hole transport layer is composed of the composite material according to any one of claims 1 to 3 or the composite material prepared by the preparation method according to any one of claims 4 to 9.