Composite material and method for producing the same, light emitting diode

Abstract

The application relates to the display technical field, and relates to a composite material and a preparation method thereof and a light emitting diode. The preparation method provided in the application comprises the following steps: a first mixed system comprising quantum dots, metal cations provided by a metal cation precursor and anions provided by an anion precursor is provided; the first mixed system is subjected to a first reaction, so that the metal cations and the anions are bonded to the surface of the quantum dots, and the metal cations bonded to the surface of the quantum dots form corresponding metal oxides, and a second mixed system is obtained; a shell cation precursor is added into the second mixed system, and a second reaction is carried out, so that shell cations provided by the shell cation precursor and the anions bonded to the surface of the quantum dots are combined to form a shell. Through the above method, the passivation effect of the dangling bonds on the surface of the quantum dots is effectively improved, and the anions bonded to the surface of the quantum dots and serving as a shell anion source promote the epitaxial growth of the shell.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of display, and particularly relates to a composite material and a preparation method thereof, and a light emitting diode. BACKGROUND

[0002] Quantum dots (QDs) are a typical nanomaterial, and the radius thereof is usually less than or close to the exciton Bohr radius, which exhibits a significant quantum confinement effect and has unique optical properties, such as long lifetime, narrow emission spectrum, controllable emission wavelength, high quantum yield, excellent monodispersity and strong photothermal stability. With the continuous improvement of the performance of quantum dot materials and the continuous optimization and improvement of other functional layers, the performance of quantum dot light emitting diodes (QLED) has been continuously improved, so that the external quantum efficiency of most red, green and blue QLED devices has exceeded 20%, and the service life has basically met the requirements of commercial application.

[0003] Quantum dots are nanoscale materials, and have a very large specific surface area. In addition, a large number of dangling bonds exist on the surface of quantum dots, and unpassivated dangling bonds are prone to form defect states and defect energy levels, which can easily cause non-radiative transition of quantum dots, thereby reducing the luminescent efficiency of quantum dots. At present, the methods for passivating the dangling bonds on the surface of quantum dots mainly include the method of modifying the surface of quantum dots with organic ligands and the method of forming a shell layer on quantum dots. However, the effect of passivating the dangling bonds on the surface of quantum dots by these methods is limited. SUMMARY

[0004] The present application aims to provide a composite material and a preparation method thereof, and aims to solve the problem of limited effect of passivating the dangling bonds on the surface of quantum dots by the existing method.

[0005] Further, the present application also provides a light emitting diode to improve the luminescent performance of the light emitting diode.

[0006] The technical scheme adopted by the present application is as follows:

[0007] In a first aspect, the present application provides a preparation method of a composite material, comprising the following steps:

[0008] providing a first mixed system comprising quantum dots, metal cations provided by a metal cation precursor and anions provided by an anion precursor;

[0009] carrying out a first reaction on the first mixed system, so that the metal cations and the anions are bonded to the surface of the quantum dots, and the metal cations bonded to the surface of the quantum dots form corresponding metal oxides, to obtain a second mixed system;

[0010] adding a shell cation precursor into the second mixed system and performing a second reaction to make shell cations provided by the shell cation precursor combine with the anions bonded on the surface of the quantum dots to form a shell.

[0011] The preparation method of the composite material provided in the present application comprises the following steps: performing a first reaction on a first mixed system comprising quantum dots, metal cations provided by a metal cation precursor, and anions provided by an anion precursor, so that the metal cations and the anions are bonded on the surface of the quantum dots, wherein the metal cations are bonded to the non-metal phase of the surface of the quantum dots, and the anions are bonded to the metal phase of the surface of the quantum dots, thereby passivating the dangling bonds on the surface of the quantum dots; in addition, the metal cations bonded on the surface of the quantum dots form corresponding metal oxides, and when the metal cation precursor is a magnetic metal source, the composite material has corresponding magnetism, so that the composite material can be uniformly deposited by applying a magnetic field in the process of film formation by using a solution method, thereby obtaining a composite material film with high flatness; at the same time, since the cation defect states on the surface of the quantum dots are passivated by the anions, the adverse effects of the formation of the metal oxides on the quantum dots can be effectively reduced, and the luminescent performance of the quantum dots is not affected. After the first reaction, a shell cation precursor is added in the method of the present application to perform a second reaction, so that shell cations provided by the shell cation precursor combine with the anions bonded on the surface of the quantum dots to form a shell, thereby further improving the passivation effect of the dangling bonds on the surface of the quantum dots, reducing the non-radiative transition of the quantum dots, and further improving the luminescent performance of the quantum dots. In addition, since the anions bonded on the surface of the quantum dots do not participate in the reaction of forming the metal oxides in the process of the first reaction, the anions can act as a source of shell anions to promote the epitaxial growth of the shell, thereby improving the synthesis quality of the composite material to some extent and being beneficial to improving the synthesis efficiency.

[0012] In a second aspect, the present application provides a composite material, comprising: quantum dots and a shell covering the quantum dots, and a metal oxide formed between the quantum dots and the shell.

[0013] The composite material provided in the second aspect of the present application is prepared by the above-mentioned preparation method, has few dangling bonds on the surface, and has high luminescent performance.

[0014] In a third aspect, the present application provides a light-emitting diode, comprising oppositely arranged bottom electrodes and top electrodes, and a light-emitting layer arranged between the bottom electrodes and the top electrodes.

[0015] The material forming the light-emitting layer comprises the composite material prepared by the above-mentioned preparation method.

[0016] The light emitting diode provided by the application has a light emitting layer formed by the composite material prepared by the preparation method, the surface of the material has few dangling bonds and non-radiative transitions, the surface of the film layer is flat, and the light emitting performance is high. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the application, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative effort.

[0018] Figure 1 is a flow chart of a preparation method of a composite material provided by an embodiment of the application;

[0019] Figure 2 is a flow chart of a preparation method of a composite material provided by another embodiment of the application;

[0020] Figure 3 is a structural schematic diagram of a composite material provided by an embodiment of the application;

[0021] Figure 4 is a structural schematic diagram of a light emitting diode provided by an embodiment of the application;

[0022] Figure 5 is a structural schematic diagram of a light emitting diode provided by another embodiment of the application;

[0023] In the drawings, 1 is an anode, 21 is a hole injection layer, 22 is a hole transport layer, 3 is a light emitting layer, 4 is an electron transport layer, and 5 is a cathode. DETAILED DESCRIPTION

[0024] In order to make the technical problems, technical solutions and beneficial effects of the application more clearly understood, the application will be further described in detail in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0025] In the application, the term "and / or" describes the association relationship of the associated objects, which means that there can be three kinds of relationships, for example, A and / or B, which can mean that A exists alone, A and B exist together, and B exists alone. Wherein A and B can be singular or plural.

[0026] It should be understood that the size of the serial number of the method steps in various embodiments of the present application does not mean the order of execution, and part or all of the steps can be executed in parallel or in sequence, and the execution order of each process should be determined according to its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

[0027] The terms "first", "second" and "third" are only for descriptive purposes, used to distinguish the objects such as substances from each other, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features.

[0028] The first aspect of the embodiments of the present application provides a preparation method of a composite material, as shown in the following steps: Figure 1

[0029] S01, providing a first mixed system including quantum dots, metal cations provided by metal cation precursors, and anions provided by anion precursors;

[0030] S02, performing a first reaction on the first mixed system, so that the metal cations and the anions are bonded on the surface of the quantum dots, and the metal cations bonded on the surface of the quantum dots form corresponding metal oxides, to obtain a second mixed system;

[0031] S03, adding shell cation precursors to the second mixed system and performing a second reaction, so that the shell cations provided by the shell cation precursors combine with the anions bonded on the surface of the quantum dots to form a shell.

[0032] Specifically, in step S01, the first mixed system includes quantum dots, metal cations provided by metal cation precursors, and anions provided by anion precursors, as a reaction system for forming metal oxides on the surface of the quantum dots subsequently.

[0033] ​The quantum dots have a nanometer scale particle size, and the material thereof can be selected from conventional quantum dot materials in the art. In some embodiments, the material of the quantum dots is selected from at least one of a group II-VI semiconductor, a group III-V semiconductor, and a group IV-VI semiconductor. Among them, the group II-VI semiconductor includes but is not limited to CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CdZnSeS, CdZnSeTe, CdZnSTe, CdHgSeS, CdHgSeTe, CdHgSTe, HgZnSeS, HgZnSeTe, and HgZnSTe, etc., the group III-V semiconductor includes but is not limited to GaN, GaP, GaAs, GaSb, AlN, AlP, AlAs, AlSb, InN, InP, InAs, InSb, GaNP, GaNAs, GaNSb, GaPAs, GaPSb, AlNP, AlNAs, AlNSb, AlPAs, AlPSb, InNP, InNAs, InNSb, InPAs, InPSb, GaAlNP, GaAlNAs, GaAlNSb, GaAlPAs, GaAlPSb, GaInNP, GaInNAs, GaInNSb, GaInPAs, GaInPSb, InAlNP, InAlNAs, InAlNSb, InAlPAs, and InAlPSb, etc., and the group IV-VI semiconductor includes but is not limited to SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe, etc. In some embodiments, the particle size of the quantum dots is 1-10 nanometers.

[0034] The metal cation precursor is used to provide metal cations, which are ionized or otherwise reacted to form metal cations by being dispersed in a solvent. The metal cations are introduced into the mixed system and, by subsequently performing the first reaction, on the one hand, the metal cations can be connected to the non-metal phase on the surface of the quantum dots through coordination bonds, thereby being bonded to the surface of the quantum dots and achieving the purpose of passivating the dangling bonds on the surface of the quantum dots; on the other hand, the metal cations bonded to the surface of the quantum dots form corresponding metal oxides, and when the metal cation precursor is a magnetic metal source, the corresponding metal oxides also have corresponding magnetism, thereby imparting certain magnetism to the composite material and promoting the preparation of a composite material film with high flatness.

[0035] In some embodiments, the metal cation precursor is a magnetic metal source, and preferably, the corresponding metal oxide formed by the magnetic metal source has corresponding magnetism, so that the composite material prepared from the magnetic metal source also has a certain degree of corresponding magnetism. In the process of forming a film of the composite material by using a solution method, a magnetic field can be applied to achieve uniform deposition of the composite material, reduce the influence of local aggregation of the composite material caused by the solvent during the solvent evaporation process, avoid the deposition of a ring with a color much darker than the middle part at the edge of the film (a "coffee ring" effect), and thus obtain a composite material film with high flatness. In further embodiments, the magnetic metal source includes at least one of an iron source, a cobalt source, a nickel source, a manganese source, and a gadolinium source. The metal oxides corresponding to these magnetic metal sources all have good ferromagnetism and can be arranged directionally in a magnetic field environment, thereby achieving the purpose of uniform deposition of the composite material. The iron source includes, but is not limited to, iron chloride, iron iodide, iron bromide, iron fluoride, iron acetate, iron acetylacetone, iron sulfate, iron nitrate, ferrous oxide, ferrous oxide, ferroferric oxide, ferrous hydroxide, iron oleate, iron myristate, iron stearate, iron palmitate, etc. The cobalt source includes, but is not limited to, ammonium cobalt sulfate, lithium cobalt oxide, cobalt carbonate, cobalt chromate, cobalt aluminate, ammonium cobalt phosphate, cobalt chloride, cobalt iodide, cobalt bromide, cobalt fluoride, cobalt acetate, cobalt acetylacetone, cobalt sulfate, cobalt nitrate, cobalt oxide, cobalt hydroxide, cobalt oleate, cobalt myristate, cobalt stearate, cobalt palmitate, etc. The nickel source includes, but is not limited to, nickel chloride, nickel sulfate, nickel nitrate, nickel fluoride, nickel bromide, nickel iodide, etc. The manganese source includes, but is not limited to, manganese carbonate, manganese chloride, manganese iodide, manganese bromide, manganese fluoride, manganese acetate, manganese acetylacetone, manganese sulfate, manganese nitrate, manganese oxide, manganese hydroxide, manganese oleate, manganese myristate, manganese stearate, manganese palmitate, etc. The gadolinium source includes, but is not limited to, gadolinium carbonate, gadolinium chloride, gadolinium iodide, gadolinium bromide, gadolinium fluoride, gadolinium acetate, gadolinium acetylacetone, gadolinium sulfate, gadolinium nitrate, gadolinium oxide, gadolinium hydroxide, gadolinium oleate, gadolinium myristate, gadolinium stearate, gadolinium palmitate, etc.

[0036] The anion precursor is used to provide an anion, which is ionized or otherwise reacted to form an anion by being dispersed in a solvent. The anion is introduced into the mixed system, and by subsequently performing the first reaction, the anion can be connected to the metal phase on the surface of the quantum dot through coordination bonding, so as to be bonded on the surface of the quantum dot, and to achieve the purpose of passivating the dangling bonds on the surface of the quantum dot. In addition, the anion can also act as a source of shell anions in the second reaction to promote the epitaxial growth of the shell, and to improve the synthesis quality and synthesis efficiency of the composite material.

[0037] In some embodiments, the anion provided by the anion precursor is an anion of a group VIA element, such as a sulfide ion, a selenide ion, and a telluride ion, etc. Such anions are conducive to forming a shell with a band gap greater than the quantum dot, and are conducive to effectively confining excitons in the quantum dot. Correspondingly, the anion precursor is a compound formed by tellurium, selenium, and sulfur elements and some organic matters, including but not limited to Se-TOP, Se-TBP, Se-TPP, Se-ODE, Se-OA, Se-ODA, Se-TOA, Se-ODPA, Se-OLA, Se-OCA (selenium octylamine), Te-TOP, Te-TBP, Te-TPP, Te-ODE, Te-OA, Te-ODA, Te-TOA, Te-ODPA, Te-OLA, Te-OCA, S-TOP, S-TBP, S-TPP, S-ODE, S-OA, S-ODA, S-TOA, S-ODPA, S-OLA, S-OCA, alkyl mercaptan (such as hexanethiol, octanethiol, decanethiol, dodecyl mercaptan, and hexadecyl mercaptan, mercaptopropyl silane), etc., wherein, TOP is the English full name of Tri-n-octylphosphine, TBP is the English full name of Tri-n-butylphosphine, TPP is the English full name of Diphenylphosphine, ODE is the English full name of 1-Octadecene, OA is the English full name of oleic acid, ODA is the English full name of octadecylamine, TOA is the English full name of trioctylamine, ODPA is the English full name of octadecylphosphonic acid, OLA is the English full name of oleylamine, and OCA is the English full name of octylamine.

[0038] On the basis of the above-mentioned embodiments, in some embodiments, the molar ratio of the metal cations to the metal atoms of the quantum dots is (0.01-1):1. When the molar ratio of the metal cations to the metal atoms of the quantum dots is less than 0.01, the amount of the metal cations is too small, which is not conducive to forming a metal oxide layer that sufficiently coats and modifies the quantum dots. When the molar ratio of the metal cations to the metal atoms of the quantum dots is greater than 1, the metal oxide layer formed is too thick, which is not conducive to carrier injection.

[0039] On the basis of the above-mentioned embodiments, in some embodiments, the molar ratio of the metal cations to the anions is (0.1-1):10. When the molar ratio of the metal cations to the anions is less than 0.01, the amount of the metal cations is too small, which is not conducive to forming a metal oxide layer that sufficiently coats and modifies the quantum dots. When the molar ratio of the metal cations to the anions is greater than 0.1, the anions cannot effectively play the role of a shell anion source to promote the epitaxial growth of the shell.

[0040] The first mixed system is a solution system, and its preparation method can refer to conventional techniques in the art, that is, the solution system only needs to uniformly disperse the quantum dots, the metal cations, and the anions.

[0041] In some embodiments, the preparation method of the first mixed system comprises:

[0042] S011, providing quantum dots, a metal cation precursor, and an anion precursor;

[0043] S012, dispersing the quantum dots, the metal cation precursor, and the anion precursor in a solvent to form a first dispersion liquid.

[0044] In step S012, the quantum dots, the metal cation precursor, and the anion precursor are dispersed in the solvent to uniformly mix the quantum dots, the metal cation precursor, and the anion precursor. Since the metal cation precursor and the anion precursor form metal cations and anions in the solvent, respectively, part of the metal cations and anions in contact with the quantum dots are bonded to the surface of the quantum dots in the first dispersion liquid, which to some extent passivates the dangling bonds on the surface of the quantum dots.

[0045] The step of dispersing the quantum dots, the metal cation precursor, and the anion precursor in the solvent can refer to conventional techniques in the art, for example, the step of dispersing the quantum dots, the metal cation precursor, and the anion precursor in the solvent is performed in an inert atmosphere to prevent interference from the external environment. The inert atmosphere includes but is not limited to an argon atmosphere, a helium atmosphere, a nitrogen atmosphere, and the like.

[0046] The solvent can be a conventional organic solvent in the art, and in some embodiments, the solvent is at least one of n-hexane, oleic acid, and octadecene.

[0047] In step S02, the first mixture is subjected to a first reaction to enable the metal cations to bond with the anions on the surface of the quantum dots, and enable the metal cations bonded on the surface of the quantum dots to form corresponding metal oxides.

[0048] In some embodiments, the first reaction is performed in an oxidizing atmosphere, and the temperature of the first reaction is lower than the reaction temperature of the metal cations and the anions, which on one hand, accelerates the coordination of the metal cations and the anions in the system with the quantum dots; on the other hand, promotes the oxidation of the metal cations to form corresponding metal oxides under the condition that the anions bonded on the surface of the quantum dots are not affected, and promotes the formation of a metal oxide layer on the surface of the quantum dots on the basis of controlling the molar ratio of the metal cations and the anions to be (0.1-1):10, thereby obtaining quantum dots with a metal oxide layer on the surface for modification. In some embodiments, the thickness of the metal oxide layer formed in step S02 is 0.5-5 nanometers.

[0049] In the present application, the oxidizing atmosphere includes a gas with oxidizing property, such as oxygen. In some embodiments, the oxidizing atmosphere is an air atmosphere.

[0050] The temperature of the first reaction is lower than the reaction temperature of the metal cations and the anions to avoid the direct reaction of the metal cations and the anions to affect the formation of the metal oxides. In some embodiments, the first reaction includes: incubating and reacting at 200-300°C for 1-90 minutes to ensure that the metal cations are completely oxidized to form corresponding metal oxides, while preventing the anions from being affected. When the reaction temperature is lower than 200°C and the reaction time is less than 1 minute, the metal cations cannot be sufficiently oxidized to form corresponding metal oxides, and at the same time, the magnetic field effect of the metal oxide layer is affected, which is not conducive to the firm anchoring of the composite material on the substrate during film formation, and affects the film formation quality; when the reaction temperature is higher than 300°C and the reaction time is greater than 90 minutes, the metal cations are oxidized to form corresponding metal oxides, while the metal cations are also prone to react with the anions to form byproducts.

[0051] In step S03, a shell cation precursor is added to the second mixture, and a second reaction is performed to enable the shell cations provided by the shell cation precursor to combine with the anions bonded on the surface of the quantum dots to form a shell.

[0052] In some embodiments, the temperature of the second reaction is greater than the temperature of the first reaction, so that the shell layer cations react with the anions bonded to the surface of the quantum dots to form the shell layer. In further embodiments, the temperature of the second reaction is 250-350°C to form the shell layer. Based on the molar ratio of the metal cations and the anions being controlled to be (0.1-1):10, the amount of the shell layer cation precursor is adjusted within the reaction range, and the thickness of the shell layer formed in step S03 is 1-10 nm.

[0053] The shell layer cation precursor is used to provide shell layer cations to form a shell layer outside the quantum dots. When the anions are sulfide ions, the shell layer formed is a sulfide shell layer; when the anions are selenide ions, the shell layer formed is a selenide shell layer; and when the anions are telluride ions, the shell layer formed is a telluride shell layer. The type of the shell layer cations can be referred to the quantum dots. In some embodiments, the element of the shell layer cations of the shell layer cation precursor is a same group element as the element of the metal atoms of the quantum dots, so that the quantum dots and the shell layer lattice are adapted.

[0054] Based on the above embodiments, in some embodiments, the anions are selenide ions or telluride ions, as shown in Figure 2 The above preparation method further includes:

[0055] S04, after the step of performing the second reaction, the shell layer cation precursor and the sulfide ion precursor are added, and a third reaction is performed, so that the shell layer cation precursor and the sulfide ion precursor are combined on the surface of the shell layer to form a protective layer.

[0056] When the anions are selenide ions or telluride ions, the shell layer prepared in step S03 is a selenide ion shell layer or a telluride ion shell layer. Since the properties of selenide and telluride are unstable, by continuing to add the shell layer cation precursor and the sulfide ion precursor in the third dispersion liquid and performing a third reaction, a layer of sulfide shell layer is grown outside the selenide ion shell layer or the telluride ion shell layer as a protective layer, so as to ensure that the prepared composite material has good stability.

[0057] The temperature and time of the third reaction can be adjusted according to the type of the shell layer cations, so that the sulfide ions provided by the shell layer cation precursor and the sulfide ion precursor can fully react. In some embodiments, the temperature of the third reaction is preferably 250-350°C.

[0058] Further, after the reaction in step S03 or step S04 is completed, solid-liquid separation is performed on the reaction liquid. In some embodiments, a precipitant is added to the reaction liquid to precipitate a precipitate, and the precipitate is washed to obtain a composite material. In some embodiments, the reaction liquid is deposited on a substrate and annealing treatment is performed.

[0059] Based on the above technical solutions, the embodiments of the present application further provide a composite material and a light emitting diode.

[0060] Accordingly, a composite material, such as a light emitting diode (LED), includes quantum dots and a shell layer covering the quantum dots, and a metal oxide layer formed between the quantum dots and the shell layer. Figure 3 As shown, the composite material includes quantum dots and a shell layer covering the quantum dots, and a metal oxide layer formed between the quantum dots and the shell layer.

[0061] In some embodiments, the material forming the shell layer is a Group VIA compound.

[0062] In further embodiments, the composite material further includes a protective layer covering the shell layer; wherein the shell layer is a selenide layer or a telluride layer, and the protective layer is a sulfide layer.

[0063] In some embodiments, the metal oxide is a magnetic metal oxide. In further embodiments, the magnetic metal oxide is at least one of iron oxide, cobalt oxide, nickel oxide, manganese oxide, and gadolinium oxide.

[0064] On the basis of the above embodiments, the particle size of the quantum dots is 1-10 nanometers, the thickness of the metal oxide layer is 0.5-5 nanometers, and the thickness of the shell layer is 1-10 nanometers.

[0065] Accordingly, the present application provides a light emitting diode as shown Figure 4 The light emitting diode includes oppositely arranged bottom electrodes 1 and top electrodes 5, and a light emitting layer 3 arranged between the bottom electrodes 1 and the top electrodes 5.

[0066] The material forming the light emitting layer 3 includes the composite material prepared by the above method.

[0067] The preparation method of the light emitting layer can refer to conventional techniques in the art, for example, a solution method is used to perform film forming treatment on the slurry containing the composite material prepared by the above method or the above composite material. The solution method includes, but is not limited to, spin coating, blade coating, or inkjet printing, etc.

[0068] On the basis of the magnetic property of the composite material prepared by the above method, in some embodiments, the step of performing film forming treatment on the slurry includes: depositing the composite material in the slurry on a substrate including a bottom electrode or a top electrode in a magnetic field environment. Since the composite material contains a magnetic metal oxide layer, by depositing the composite material solution on the substrate in a magnetic field environment, the purpose of uniformly depositing the composite material can be achieved, thereby obtaining a film layer with high flatness.

[0069] The structure of the light emitting diode can refer to the conventional technology in the art. In some embodiments, the light emitting diode is of a normal structure, and the anode is connected to the substrate as a bottom electrode. In other embodiments, the light emitting diode is of an inverted structure, and the cathode is connected to the substrate as a bottom electrode. Further, in addition to the basic functional film layers such as the cathode, the anode and the light emitting layer, a hole functional layer such as a hole injection layer, a hole transport layer and a hole blocking layer can be arranged between the anode and the light emitting layer, and an electron functional layer such as an electron injection layer, an electron transport layer and an electron blocking layer can be arranged between the light emitting layer and the cathode.

[0070] As shown in some embodiments, Figure 5 the light emitting diode comprises an anode 1, a hole injection layer 21, a hole transport layer 22, a light emitting layer 3, an electron transport layer 4 and a cathode 5, wherein the anode 1 is connected to the substrate as a bottom electrode, the hole injection layer 21 is arranged between the anode 1 and the light emitting layer 3, the hole transport layer 22 is arranged between the hole injection layer 21 and the light emitting layer 3, and the electron transport layer 4 is arranged between the light emitting layer 3 and the cathode 5.

[0071] In the light emitting diode, the materials and thicknesses of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer and the cathode can refer to the conventional technology in the art.

[0072] The substrate includes a rigid substrate and a flexible substrate. In some embodiments, the substrate is selected from at least one of glass, a silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide and polyethersulfone.

[0073] The anode includes a conductive metal and / or a conductive metal oxide. The conductive metal includes, but is not limited to, nickel, platinum, vanadium, chromium, copper, zinc and gold, or an alloy thereof. The conductive metal oxide includes, but is not limited to, zinc oxide, indium oxide, tin oxide, indium tin oxide (ITO), indium zinc oxide (IZO), fluorine-doped tin oxide and the like.

[0074] The material of the hole injection layer is selected from a material having good hole injection performance, including, but not limited to, poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS), copper phthalocyanine (CuPc), 2,3,5,6-tetrafluoro-7,7',8,8'-tetracyanoquinodimethane (F4-TCNQ), 2,3,6,7,10,11-hexacyano-1,4,5,8,9,12-hexaazatriphenylene (HATCN), a doped or undoped transition metal oxide, a doped or undoped metal chalcogenide and the like. The transition metal oxide includes, but is not limited to, MoO3, VO2, WO3, CuO and the like. The metal chalcogenide includes, but is not limited to, MoS2, MoSe2, WS2, WSe2, CuS and the like. The thickness of the hole injection layer is preferably 10-150 nm.

[0075] The material of the hole transport layer is selected as an organic material with good hole transport capability, including but not limited to poly(9,9-dioctylfluorene-CO-N-(4-butylphenyl)diphenylamine) (TFB), polyvinylcarbazole (PVK), poly(N,N'bis(4-butylphenyl)-N,N'-bis(phenyl)phenylamine) (Poly-TPD), poly(9,9-dioctylfluorene-co-bis-N,N-phenyl-1,4-phenylenediamine) (PFB), 4,4',4"-tris(carbazol-9-yl)triphenylamine (TCTA), 4,4'-bis(9-carbazolyl) biphenyl (CBP), N,N'-diphenyl-N,N'-di(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD), N,N'-diphenyl-N,N'-(1-naphthyl)-1,1'-biphenyl-4,4'-diamine (NPB), doped graphene, undoped graphene, C60, etc. The thickness of the hole transport layer is preferably 10-150 nm.

[0076] The material of the electron transport layer is selected as a material with good electron transport performance, including but not limited to ZnO, TiO2, Alq3, SnO, ZrO, AlZnO, ZnSnO, BCP, TAZ, PBD, TPBI, Bphen, CsCO3, etc. The thickness of the electron transport layer is preferably 10-100 nm.

[0077] The cathode can be selected as a single metal or an alloy thereof, including but not limited to at least one of magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, lead, cesium, barium; or, the cathode is selected as a multi-layer structure material, including but not limited to alkali metal halides, alkaline earth metal halides, alkali metal oxides, etc.; or, the cathode is selected as a combination of a multi-layer structure material and a metal layer, and the metal layer is selected as an alkaline earth metal and / or a group 13 metal, including but not limited to LiF / Al, LiO2 / Al, LiF / Ca, Liq / Al, and BaF2 / Ca, etc.

[0078] In order to make the above-mentioned implementation details and operations of the present application clearly understood by those skilled in the art, and the performance of the composite material and its preparation method, the preparation method of the film layer and the light-emitting diode is significantly embodied, the following examples are used to illustrate the implementation of the present application.

[0079] Example 1

[0080] The present embodiment provides a composite material, and its specific preparation method is as follows:

[0081] 1) The quantum dots are selected as CdZnSe quantum dots with a peak wavelength of 520 nm and a peak width of 24 nm in n-hexane solution, with a volume of 10 mL and a concentration of 10 mg / mL;

[0082] 2) Under argon atmosphere, CdZnSe quantum dots were added into 5 mL of oleic acid and 25 mL of octadecene mixed solvent, and then 0.1 mmol of gadolinium chloride and 0.5 mmol of Se-TOP solution were added after degassing at 120 °C for 60 min, and then the air atmosphere was switched to and the temperature was raised to 200 °C and kept for 90 min to obtain a second dispersion liquid in which CdZnSe / gadolinium oxide layer was dispersed;

[0083] 3) 2 mmol of zinc oleate solution was added into the second dispersion liquid, and the temperature was raised to 300 °C to obtain a third dispersion liquid in which CdZnSe / gadolinium oxide layer / ZnSe was dispersed;

[0084] 4) 4 mmol of zinc oleate solution was added into the third dispersion liquid, and the temperature was raised to 300 °C, and then 2 mmol of S-TOP was added and reacted for 60 min; after the reaction was completed, the reaction product was dissolved in n-hexane, precipitated in ethanol, and centrifuged to obtain a composite material CdZnSe / gadolinium oxide layer / ZnSe / ZnS.

[0085] Comparative Example 1-1

[0086] This comparative example provides a composite material, and the preparation method thereof is basically the same as that of Example 1, except that step 2) is omitted, and 0.5 mmol of Se-TOP is further added before the temperature is raised in step 3) to obtain a composite material CdZnSe / ZnSe / ZnS.

[0087] Comparative Example 1-2

[0088] This comparative example provides a composite material, and the preparation method thereof is basically the same as that of Example 1, except that Se-TOP is not added in step 2), and 0.5 mmol of Se-TOP is further added before the temperature is raised in step 3).

[0089] Example 2

[0090] This example provides a composite material, and the preparation method thereof is basically the same as that of Example 1, except that the quantum dots are CdZnSe quantum dots with an emission peak wavelength of 465 nm and a peak width of 28 nm; in step 2), 4 mL of oleic acid, 26 mL of octadecene, and 0.08 mmol of gadolinium chloride are used, and the temperature is kept at 200 °C for 60 min; in step 3), 3 mmol of zinc oleate is used; and in step 4), 3 mmol of zinc oleate and 1 mmol of S-TOP are used.

[0091] Comparative Example 2-1

[0092] The comparative example provides a composite material, the preparation method of which is basically same with that of example 2, the difference is that step 2) is omitted, and 0.5mmol Se-TOP is further added before heating in step 3), to obtain the composite material CdZnSe / ZnSe / ZnS.

[0093] Comparative example 2-2

[0094] The comparative example provides a composite material, the preparation method of which is basically same with that of example 2, the difference is that Se-TOP is not added in step 2), and 0.5mmol Se-TOP is further added before heating in step 3).

[0095] Example 3

[0096] The example provides a composite material, the preparation method of which is basically same with that of example 1, the difference is that the quantum dot is selected as CdSe quantum dot with emission peak wavelength of 620nm and peak width of 25nm; in step 2), oleic acid is 10mL, octadecene is 20mL, gadolinium chloride is replaced by manganese chloride, and the manganese chloride is 0.12mmol, and the reaction is kept at 230℃ for 80min; in step 3), zinc oleate is 4mmol; in step 4), S-TOP is 3mmol, to obtain the composite material CdSe / manganese oxide / ZnSe / ZnS.

[0097] Comparative example 3-1

[0098] The comparative example provides a composite material, the preparation method of which is basically same with that of example 3, the difference is that step 2) is omitted, and 0.5mmol Se-TOP is further added before heating in step 3), to obtain the composite material CdSe / ZnSe / ZnS.

[0099] Comparative example 3-2

[0100] The comparative example provides a composite material, the preparation method of which is basically same with that of example 3, the difference is that Se-TOP is not added in step 2), and 0.5mmol Se-TOP is further added before heating in step 3).

[0101] Example 4

[0102] The example provides a composite material, the preparation method of which is basically same with that of example 1, the difference is that in step 2), gadolinium chloride is replaced by manganese chloride, Se-TOP is 0.3mmol, and the reaction is kept at 210℃ for 80min; in step 4), S-TOP is 1.5mmol.

[0103] Comparative example 4-1

[0104] The comparative example provides a composite material, the preparation method of which is basically same with that of example 4, the difference is that step 2) is omitted, and 0.5mmol Se-TOP is further added before heating in step 3), to obtain the composite material CdZnSe / ZnSe / ZnS.

[0105] Comparative example 4-2

[0106] The comparative example provides a composite material, the preparation method of which is basically same with that of example 4, the difference is that Se-TOP is not added in step 2), and 0.3mmol Se-TOP is further added before heating in step 3).

[0107] Example 5

[0108] The example provides a composite material, the preparation method of which is basically same with that of example 1, the difference is that the quantum dots are selected as CdZnSe quantum dots with an emission peak wavelength of 465nm and a peak width of 28nm; in step 2), 4mL of oleic acid, 26mL of octadecene, and cobalt chloride is used to replace gadolinium chloride, and the cobalt chloride is 0.08mmol, the Se-TOP is 0.8mmol, and the reaction is kept at 230℃ for 60min; in step 3), 3mmol of zinc oleate; in step 4), 3mmol of zinc oleate and 1.5mmol of S-TOP.

[0109] Comparative example 5-1

[0110] The comparative example provides a composite material, the preparation method of which is basically same with that of example 5, the difference is that step 2) is omitted, and 0.8mmol Se-TOP is further added before heating in step 3), to obtain the composite material CdZnSe / ZnSe / ZnS.

[0111] Comparative example 5-2

[0112] The comparative example provides a composite material, the preparation method of which is basically same with that of example 5, the difference is that Se-TOP is not added in step 2), and 0.8mmol Se-TOP is further added before heating in step 3).

[0113] Example 6

[0114] The example provides a composite material, the preparation method of which is basically same with that of example 1, the difference is that the quantum dots are selected as CdSe quantum dots with an emission peak wavelength of 620nm and a peak width of 25nm; in step 2), 10mL of oleic acid, 20mL of octadecene, and nickel chloride is used to replace gadolinium chloride, and the nickel chloride is 0.12mmol, the Se-TOP is 1.3mmol, and the reaction is kept at 250℃ for 50min; in step 3), 4mmol of zinc oleate; in step 4), 3.4mmol of S-TOP.

[0115] Comparative Example 6-1

[0116] The comparative example provides a composite material, the preparation method of which is basically the same as that of Example 5, except that step 2) is omitted, and 1.3 mmol Se-TOP is further added before heating in step 3), to obtain a composite material CdSe / ZnSe / ZnS.

[0117] Comparative Example 6-2

[0118] The comparative example provides a composite material, the preparation method of which is basically the same as that of Example 5, except that no Se-TOP is added in step 2), and 1.3 mmol Se-TOP is further added before heating in step 3).

[0119] Example 7

[0120] The example provides a bottom-emitting light-emitting diode, the preparation method of which comprises sequentially depositing an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light-emitting layer is the thin film prepared in Example 1 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0121] Comparative Example 7-1

[0122] The comparative example provides a light-emitting diode which is basically the same as that of Example 7, except that the light-emitting layer is the thin film prepared in Comparative Example 1-1.

[0123] Comparative Example 7-2

[0124] The comparative example provides a light-emitting diode which is basically the same as that of Example 7, except that the light-emitting layer is the thin film prepared in Comparative Example 1-2.

[0125] Example 8

[0126] The example provides a bottom-emitting light-emitting diode, the preparation method of which comprises sequentially depositing an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light-emitting layer is the thin film prepared in Example 2 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0127] Comparative Example 8-1

[0128] The light emitting diode provided by the present comparative example is basically the same as that of Example 8, except that the light emitting layer is the thin film prepared in Comparative Example 2-1.

[0129] Comparative Example 8-2

[0130] The light emitting diode provided by the present comparative example is basically the same as that of Example 8, except that the light emitting layer is the thin film prepared in Comparative Example 2-2.

[0131] Example 9

[0132] The present example provides a bottom-emitting light emitting diode, and the preparation method thereof comprises: sequentially depositing an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light emitting layer is the thin film prepared in Example 3 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0133] Comparative Example 9-1

[0134] The light emitting diode provided by the present comparative example is basically the same as that of Example 9, except that the light emitting layer is the thin film prepared in Comparative Example 3-1.

[0135] Comparative Example 9-2

[0136] The light emitting diode provided by the present comparative example is basically the same as that of Example 9, except that the light emitting layer is the thin film prepared in Comparative Example 3-2.

[0137] Example 10

[0138] The present example provides a bottom-emitting light emitting diode, and the preparation method thereof comprises: sequentially depositing an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light emitting layer is the thin film prepared in Example 4 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0139] Comparative Example 10-1

[0140] The light emitting diode provided by the present comparative example is basically the same as that of Example 10, except that the light emitting layer is the thin film prepared in Comparative Example 4-1.

[0141] Comparative Example 10-2

[0142] The light emitting diode provided by the present comparative example is basically the same as that of Example 10, except that the light emitting layer is the thin film prepared in Comparative Example 4-2.

[0143] Example 11

[0144] The present example provides a bottom-emitting light emitting diode, and the preparation method thereof comprises: sequentially depositing an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light emitting layer is the thin film prepared in Example 5 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0145] Comparative Example 11-1

[0146] The light emitting diode provided by the present comparative example is basically the same as that of Example 11, except that the light emitting layer is the thin film prepared in Comparative Example 5-1.

[0147] Comparative Example 11-2

[0148] The light emitting diode provided by the present comparative example is basically the same as that of Example 11, except that the light emitting layer is the thin film prepared in Comparative Example 5-2.

[0149] Example 12

[0150] The present example provides a bottom-emitting light emitting diode, and the preparation method thereof comprises: sequentially depositing an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode on a substrate. The substrate is a glass substrate; the bottom electrode is ITO with a thickness of 80 nm; the hole injection layer is PEDOT:PSS with a thickness of 60 nm; the hole transport layer is TFB with a thickness of 100 nm; the light emitting layer is the thin film prepared in Example 6 with a thickness of 60 nm; the electron transport layer is ZnO with a thickness of 50 nm; and the top electrode is Al with a thickness of 50 nm.

[0151] Comparative Example 12-1

[0152] The light emitting diode provided by the present comparative example is basically the same as that of Example 12, except that the light emitting layer is the thin film prepared in Comparative Example 6-1.

[0153] Comparative Example 12-2

[0154] The light emitting diode provided by the present comparative example is basically the same as that of Example 12, except that the light emitting layer is the thin film prepared in Comparative Example 6-2.

[0155] The light emitting diodes prepared in Examples 7-12 and Comparative Examples were detected for external quantum efficiency (EQE) by using an EQE optical testing instrument, and the results are shown in Table 1.

[0156] wherein the ratio of the number of electron-hole pairs injected into the composite material to the number of photons emitted, in %, is an important parameter for measuring the quality of the electroluminescent device, and the specific calculation formula of EQE is as follows:

[0157]

[0158] wherein η e is the light output coupling efficiency, η r is the ratio of the number of carriers recombined to the number of carriers injected, χ is the ratio of the number of excitons generating photons to the total number of excitons, K R is the radiative process rate, and K NR is the non-radiative process rate.

[0159] Table 1

[0160] EQE (%) EQE (%) Example 7 15.1 Example 10 14.8 Comparative Example 7-1 10.2 Comparative Example 10-1 9.8 Comparative Example 7-2 7.5 Comparative Example 10-2 6.9 Example 8 8.4 Example 11 7.9 Comparative Example 8-1 6.2 Comparative Example 11-1 5.9 Comparative Example 8-2 5.6 Comparative Example 11-2 5.1 Example 9 17.5 Example 12 16.7 Comparative Example 9-1 15.4 Comparative Example 12-1 14.6 Comparative Example 9-2 9.6 Comparative Example 12-2 8.9

[0161] The above description is merely the preferred embodiments of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of producing a composite material, characterized by, The method comprises the following steps: providing a first mixture system comprising quantum dots, metal cations provided by a metal cation precursor, and anions provided by an anion precursor; carrying out a first reaction on the first mixture system, so that the metal cations and the anions are bonded to the surface of the quantum dots, and the metal cations bonded to the surface of the quantum dots form corresponding metal oxides, to obtain a second mixture system; adding a shell cation precursor to the second mixture system and carrying out a second reaction, so that shell cations provided by the shell cation precursor combine with the anions bonded to the surface of the quantum dots to form a shell; after the step of carrying out the second reaction, adding the shell cation precursor and a sulfur ion precursor and carrying out a third reaction, so that the shell cation precursor and the sulfur ion precursor combine on the surface of the shell to form a protective layer.

2. The production method according to claim 1, wherein The metal cation precursor is a magnetic metal source, The anion precursor provides anion of Group VIA element.

3. The production method according to claim 2, wherein The magnetic metal source includes at least one of iron source, cobalt source, nickel source, manganese source, and gadolinium source, The anion is at least one of sulfur ion, selenium ion, and tellurium ion.

4. The production method according to claim 1, wherein The first reaction is carried out in an oxidizing atmosphere, and the temperature of the first reaction is less than the reaction temperature of the metal cations and the anions; and / or The temperature of the second reaction is greater than the temperature of the first reaction.

5. The production method according to claim 4, wherein The first reaction includes: holding at 200-300°C for 1-90 minutes; and / or The temperature of the second reaction is 250-350°C.

6. The preparation method of claim 1, wherein the molar ratio of the metal cations to the metal atoms of the quantum dots is (0.01-1) : 1; and / or The molar ratio of the metal cations to the anions is (0.1-1) :

10.

7. The production method according to any one of claims 1 to 6, wherein The element of the shell cation of the shell cation precursor is a same-group element as the element of the metal atoms of the quantum dots; and / or The material of the quantum dots is selected from at least one of Group II-VI semiconductor, Group III-V semiconductor, and Group IV-VI semiconductor.

8. A composite material, characterized by The composite material comprises: quantum dots and a shell layer covering the quantum dots, and a metal oxide is formed between the quantum dots and the shell layer, and anions and metal cations of the metal oxide are bonded to the surface of the quantum dots, shell cations combine with the anions bonded to the surface of the quantum dots to form a shell layer, and the composite material further comprises a protective layer covering the shell layer, the protective layer is a sulfide layer, and the protective layer is the outermost layer.

9. The composite material of claim 8, wherein, The material forming the shell layer is Group VIA compound, The metal oxide is a magnetic metal oxide.

10. The composite material of claim 9, wherein The shell layer is at least one of sulfide layer, selenide layer, and telluride layer, The magnetic metal oxide is at least one of iron oxide, cobalt oxide, nickel oxide, manganese oxide, and gadolinium oxide.

11. A light emitting diode, comprising: comprising a light emitting layer, the material forming the light emitting layer comprising a composite material produced by the production method according to any one of claims 1 to 7 or a composite material according to any one of claims 8 to 10.

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