Composite Material, Its Preparation Method and Light-Emitting Diode

Abstract

The present application relates to the field of display technologies, and provides a composite material, a preparation method thereof, and a light-emitting diode. The composite material provided by the present application includes luminescent quantum dots, non-luminescent quantum dots, and a linking ligand, and the linking ligand connects the luminescent quantum dots and the non-luminescent quantum dots. In this way, the non-luminescent quantum dots are used as protective quantum dots and the surface of the luminescent quantum dots is modified by combining with the linking ligand, effectively filling the surface defects of the luminescent quantum dots without affecting the optical properties of the luminescent quantum dots, and improving the optical stability of the quantum dot material; at the same time, the non-luminescent quantum dots are connected to the luminescent quantum dots through the linking ligand, effectively increasing the distance between the luminescent quantum dots, avoiding aggregation, and improving the energy utilization efficiency, which is beneficial to obtaining a composite material with ultra-high monochromaticity and excellent luminescent performance.

Description

Technical Field

[0001] This application belongs to the field of display technology, and particularly relates to a composite material and a preparation method thereof, and a light-emitting diode. Background Art

[0002] Quantum dots are a typical class of nanomaterials with a radius usually less than or close to the exciton Bohr radius, showing a significant quantum dot confinement effect and having unique optical properties, such as: the emission spectrum can be continuously adjusted with the size and composition of the material itself, the full width at half maximum is narrow, the fluorescence efficiency is high, the lifetime is long, excellent monodispersity, and strong photothermal stability. These unique properties make them widely used in the fields of display, lighting, biological labeling, and solar cells.

[0003] Compared with traditional spherical or quasi-spherical zero-dimensional quantum dots, two-dimensional nano quantum dots not only have the basic characteristics of general quantum dots, but also show characteristics different from zero-dimensional quantum dots. For example, the peak width of zero-dimensional quantum dots is usually above 20 nm, which cannot meet the standard of the peak width <15 nm for ultra-monochromaticity requirements, while the peak width of two-dimensional nano quantum dots is usually <15 nm, which can significantly improve the monochromaticity of the device and is of great significance for realizing quantum dot light-emitting diodes (QLEDs) with high color purity.

[0004] In the existing technology, during the shell growth process of the synthesized two-dimensional nano core-shell structure quantum dots, the shell growth usually occurs on the entire surface of the core (the vertical direction of the plane direction of the core). Since the confinement effect of two-dimensional nano core-shell structure quantum dots only occurs in the thickness direction, conventional shell growth is prone to cause wavelength red shift. However, when the shell growth only occurs in the vertical direction of the plane direction of the core, there are often a large number of surface defects on the plane direction surface, which affects the luminescence performance of the light-emitting diode with two-dimensional nano quantum dots as the luminescent layer material. Summary of the Invention

[0005] The purpose of this application is to provide a composite material and a preparation method thereof, and a light-emitting diode, aiming to solve the problem that a large number of surface defects often exist on the surface of existing quantum dots, which affects the luminescence performance of the light-emitting diode.

[0006] To achieve the above application purpose, the technical solution adopted in this application is as follows:

[0007] In the first aspect, this application provides a composite material, including luminescent quantum dots, non-luminescent quantum dots, and a linking ligand, and the linking ligand connects the luminescent quantum dots and the non-luminescent quantum dots.

[0008] In the composite material provided by the present application, the non-luminescent quantum dots modify the luminescent quantum dots through surface modification with a linking ligand, effectively filling the surface defects of the luminescent quantum dots without affecting the optical properties of the luminescent quantum dots, playing the role of protecting the luminescent quantum dots as protective quantum dots, avoiding the influence of external environmental factors such as water and oxygen invasion on the optical properties of the luminescent quantum dots, thereby improving the optical stability of the quantum dot material; on the other hand, connecting the non-luminescent quantum dots to the luminescent quantum dots through a linking ligand can effectively increase the distance between the luminescent quantum dots, avoid aggregation, and reduce the occurrence of resonance energy transfer caused by too small a distance between the luminescent quantum dots, effectively improving the energy utilization efficiency, being conducive to improving the luminescence efficiency of the material, and thus obtaining a composite material with ultra-high monochromaticity and excellent luminescence performance.

[0009] Second, the present application provides a method for preparing a composite material, including the following steps:

[0010] Providing luminescent quantum dots, non-luminescent quantum dots, a linking ligand, and an acid;

[0011] Mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in a solvent to obtain the composite material.

[0012] In the method for preparing the composite material provided by the present application, using luminescent quantum dots, non-luminescent quantum dots, and a linking ligand as raw materials and adding an acid, in the step of mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in a solvent, the acid is used to eliminate the surface defect states of the luminescent quantum dots and the non-luminescent quantum dots, so as to promote the linking ligand to link the luminescent quantum dots and the non-luminescent quantum dots respectively, thereby effectively connecting the luminescent quantum dots and the non-luminescent quantum dots, and further obtaining the above-mentioned composite material with ultra-high monochromaticity and excellent luminescence performance. The method is simple, easy to operate, and suitable for large-scale production.

[0013] Preferably, the step of mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in a solvent includes:

[0014] Adding the luminescent quantum dots, the acid, and the linking ligand into a solvent, mixing and stirring at 80 °C - 200 °C for 10 minutes to 12 hours to obtain a first solution;

[0015] Adding the non-luminescent quantum dots into the first solution, and mixing and stirring at 80 °C - 200 °C for 10 minutes to 12 hours.

[0016] Preferably, the luminescent quantum dots are two-dimensional nano quantum dots;

[0017] More preferably, the non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nano quantum dots.

[0018] Further preferably, the molar ratio of the acid to the total of the luminescent quantum dots and the non-luminescent quantum dots is (0.1 - 2):10;

[0019] Further preferably, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid.

[0020] Preferably, the luminescent quantum dots have a core-shell structure, and the shell layer of the luminescent quantum dots grows only along its planar direction;

[0021] Further preferably, the non-luminescent quantum dots are connected to two planes in the thickness direction of the luminescent quantum dots.

[0022] Preferably, the non-luminescent quantum dots are non-core-shell structure quantum dots, the metal element of the non-luminescent quantum dots is in the same group as the metal element of the shell layer of the luminescent quantum dots, and / or the non-metal element of the non-luminescent quantum dots is in the same group as the non-metal element of the shell layer of the luminescent quantum dots;

[0023] Further preferably, the shell layer material of the luminescent quantum dots is a II-VI group semiconductor material, and the core material of the luminescent quantum dots is a II-VI group semiconductor material or a III-V group semiconductor material;

[0024] Further preferably, the material of the non-luminescent quantum dots is a II-VI group semiconductor material.

[0025] Preferably, the linking ligand includes a first linking group for linking the luminescent quantum dots and a second linking group for linking the non-luminescent quantum dots, and the first linking group and the second linking group are each independently selected from any one of a mercapto group, a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, and a phosphate group;

[0026] Further preferably, the linking ligand is selected as mercaptoalkanoic acid.

[0027] Preferably, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1:(10 - 100); and / or

[0028] The molar ratio of the luminescent quantum dots to the linking ligand is 1:(1 - 100).

[0029] In a third aspect, the present application provides a light-emitting diode, including a light-emitting layer, and the material of the light-emitting layer includes: the aforementioned composite material, or the composite material prepared by the above preparation method.

[0030] For the light-emitting diode provided by the present application, the material of its light-emitting layer includes the above composite material with ultra-high monochromaticity and excellent light-emitting performance, which improves the light-emitting stability of the light-emitting diode, has high light color purity, and excellent light-emitting performance. Description of the Drawings

[0031] Figure 1 is a flowchart of a method for preparing a composite material provided in an embodiment of the present application;

[0032] Figure 2 is a flowchart of a method for preparing a composite material provided in another embodiment of the present application;

[0033] Figure 3 is a schematic structural diagram of a light-emitting diode provided in an embodiment of the present application;

[0034] Figure 4 is a schematic structural diagram of a light-emitting diode provided in another embodiment of the present application;

[0035] Among them, each reference numeral in the figure: 1 - anode, 21 - hole injection layer, 22 - hole transport layer, 3 - light-emitting layer, 4 - electron transport layer, 5 - cathode. Detailed implementation manners

[0036] In order to make the technical problems to be solved, technical solutions and beneficial effects of the present application clearer, the present application will be further described in detail below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0037] In this specification, the term "and / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Wherein A and B may be singular or plural. The character " / " generally represents an "or" relationship between the associated objects before and after.

[0038] In this specification, unless otherwise specified, the term "two-dimensional nano quantum dot" refers to a flaky (planar) nano quantum dot, that is, the length and width are greater than the thickness, so that it can be approximately regarded as a two-dimensional nano quantum dot. The term "plane direction of the two-dimensional nano quantum dot" refers to the extension direction of the plane of the two-dimensional nano quantum dot, that is, the direction of length × width, which is different from the thickness direction of the two-dimensional nano quantum dot. "The shell layer of the light-emitting quantum dot only grows along its plane direction" means that the shell layer only grows from the edge of the two-dimensional nano quantum dot along its plane direction and does not grow on the plane in the thickness direction of the two-dimensional quantum dot.

[0039] An embodiment of the present application provides a composite material, including a light-emitting quantum dot, a non-light-emitting quantum dot, and a linking ligand, and the linking ligand connects the light-emitting quantum dot and the non-light-emitting quantum dot.

[0040] In the embodiments of the present application, a luminescent quantum dot refers to a class of luminescent materials that emit intrinsic light under optoelectronic effects. Compared with luminescent quantum dots, non-luminescent quantum dots emit non-intrinsic light under optoelectronic effects, such as surface state defect luminescence, or do not emit light at all under optoelectronic effects.

[0041] In the embodiments of the present application, non-luminescent quantum dots are connected to luminescent quantum dots through a linking ligand, avoiding the adverse effects caused by the linking ligand connecting two luminescent quantum dots at the same time, such as causing fluorescence quenching or resulting in an overly broad emission peak that fails to meet the requirement of ultra-high monochromaticity, thereby ensuring good luminescence performance of the quantum dots.

[0042] In some embodiments, the luminescent quantum dots are two-dimensional nano quantum dots. Compared with traditional spherical or quasi-spherical zero-dimensional quantum dots, the two-dimensional nano quantum dots meet the standard of an emission peak width < 15 nm for the requirement of ultra-high monochromaticity. Setting the luminescent quantum dots as two-dimensional nano quantum dots endows the composite material with ultra-high monochromaticity.

[0043] Based on the previous embodiment, the luminescent quantum dots have a core-shell structure, and the shell layer of the luminescent quantum dots grows only along its planar direction. In this way, the problem that two-dimensional nano quantum dots without a core-shell structure are easily invaded by external water and oxygen, reducing the luminescence efficiency, is overcome; at the same time, the shell layer of the luminescent quantum dots grows only along the planar direction of the two-dimensional nano quantum dots, avoiding the problem of red shift of the emission wavelength caused by the growth of the shell layer along the thickness direction of the two-dimensional nano quantum dots, ensuring the ultra-high monochromaticity of the luminescent quantum dots; moreover, by selecting this type of quantum dots, non-luminescent quantum dots can be mainly coated and modified on both side surfaces of the luminescent quantum dots in the thickness direction where no shell layer material grows, so that while increasing the thickness of the luminescent quantum dots themselves, their optical properties are not affected. In a further embodiment, non-luminescent quantum dots are connected to the two planes in the thickness direction of the luminescent quantum dots, so that the non-luminescent quantum dots coat and modify the two side surfaces in the thickness direction of the luminescent quantum dots, equivalent to forming a protective shell layer on these two side surfaces to fill the surface defects on the two side surfaces in the thickness direction of the luminescent quantum dots, thereby playing a role in protecting the luminescent quantum dots.

[0044] On the basis of the previous embodiment, the non-luminescent quantum dots are non-core-shell structure quantum dots, the metal elements of the non-luminescent quantum dots are in the same group as the metal elements of the shell layer of the luminescent quantum dots, and / or the non-metal elements of the non-luminescent quantum dots are in the same group as the non-metal elements of the shell layer of the luminescent quantum dots. Compared with the core-shell structure quantum dots, the non-core-shell structure quantum dots have more surface defects, and mainly emit light from surface defect states under optoelectronic action, covering the intrinsic luminescence. Selecting the non-luminescent quantum dots as non-core-shell structure quantum dots can ensure that the luminescence performance of the luminescent quantum dots themselves is not affected while giving full play to the protective effect of the non-luminescent quantum dots; on the other hand, the metal elements of the non-luminescent quantum dots are in the same group as the metal elements of the shell layer of the luminescent quantum dots, and / or the non-metal elements of the non-luminescent quantum dots are in the same group as the non-metal elements of the shell layer of the luminescent quantum dots, so as to ensure the consistency and continuity of the energy level structures of the luminescent quantum dots and the non-luminescent quantum dots. Especially when the non-luminescent quantum dots are used as the protective shell layer in the thickness direction of the luminescent quantum dots, it can ensure that the energy levels of the luminescent quantum dots are continuous in the thickness direction, thereby improving the effective binding effect of excitons and improving the luminescence performance of the composite material to a certain extent.

[0045] Based on the previous embodiment, the shell material of the luminescent quantum dots is a II-VI group semiconductor material, and the core material of the luminescent quantum dots is a II-VI group semiconductor material or a III-V group semiconductor material. Among them, the II-VI group semiconductor materials include but are 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, HgZnSTe, etc., and the III-V group semiconductor materials include but are 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, InAlPSb, etc.

[0046] The non-luminescent quantum dots can be zero-dimensional quantum dots or two-dimensional nano quantum dots. In some embodiments, the non-luminescent quantum dots are quantum dots formed by introducing water and oxygen during the reaction, so that a large number of defect states are generated on the surface of the finally formed quantum dots. When the quantum dots are excited by light or electricity, the generated excitons are easily trapped by the defect states, so that the quantum dots do not emit light or emit defect state light. Preferably, the material of the non-luminescent quantum dots is a II-VI group semiconductor material, and setting the material of the non-luminescent quantum dots to be the same as the shell material of the above-mentioned luminescent quantum dots is beneficial to ensuring the consistency and continuity of the energy level structures of the two quantum dots and improving the effective binding effect of excitons.

[0047] On the basis of the above embodiments, the length of the luminescent quantum dots is 10 - 100 nanometers, the width is 2 - 10 nanometers, and the thickness is 1 - 5 nanometers; the particle size of the non-luminescent quantum dots is 3 - 15 nm. Thus, the luminescent quantum dots are two-dimensional nano quantum dots, and the non-luminescent quantum dots are zero-dimensional quantum dots. By adjusting the sizes of the luminescent quantum dots and the non-luminescent quantum dots within the above ranges, the arrangement of the non-luminescent quantum dots in the thickness direction of the luminescent quantum dots is made more dense.

[0048] On the basis of the above embodiments, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1:(10 - 100). When the mass ratio of the non-luminescent quantum dots to the luminescent quantum dots is less than 10:1, it is likely that the non-luminescent quantum dots as protective quantum dots cannot completely coat the surface defects of the luminescent quantum dots, thereby reducing the luminescence performance of the device; when the mass ratio of the non-luminescent quantum dots to the luminescent quantum dots is greater than 100:1, the non-luminescent quantum dots as protective quantum dots are in excess. Since the non-luminescent quantum dots cannot emit light or emit defective-state light, it is likely to reduce the luminescence performance of the device. In specific embodiments, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots can be 1:10, 1:20, 1:30, 1:35, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100.

[0049] The linking ligand, as a ligand for linking the luminescent quantum dots and the non-luminescent quantum dots, should contain linking groups capable of binding to the luminescent quantum dots and the non-luminescent quantum dots, and can be a bidentate ligand or a monodentate ligand. In some embodiments, the linking ligand includes a first linking group for linking the luminescent quantum dots and a second linking group for linking the non-luminescent quantum dots; the first linking group and the second linking group are each independently selected from any one of mercapto, carboxyl, hydroxyl, sulfonic acid group, amino and phosphate groups. These groups can coordinate with the metal atoms on the surface of the quantum dots to achieve the connection between the luminescent quantum dots and the non-luminescent quantum dots. In a further embodiment, the linking ligand is selected as mercaptoalkanoic acid, where mercaptoalkanoic acid includes but is not limited to 5-mercaptopentanoic acid, 8-mercaptooctanoic acid, 7-mercaptoheptanoic acid, 11-mercaptoundecanoic acid, etc. This type of mercaptoalkanoic acid contains two groups, mercapto and carboxyl, and there is good coordination activity between these two groups and the metal atoms on the surface of the quantum dots, which can firmly connect the luminescent quantum dots and the non-luminescent quantum dots; moreover, this type of mercaptoalkanoic acid is a straight-chain structure compound, which firmly connects the luminescent quantum dots and the non-luminescent quantum dots while avoiding the distance between the luminescent quantum dots and the non-luminescent quantum dots from being too small.

[0050] In some embodiments, the molar ratio of the luminescent quantum dots to the linking ligand is 1:(1 - 100), ensuring that the linking ligand fully links the non-luminescent quantum dots and the luminescent quantum dots to enhance the luminescence performance of the material. In specific embodiments, the molar ratio of the luminescent quantum dots to the linking ligand is 1:1, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90 or 1:100.

[0051] Based on the above technical solution, in the second aspect of the embodiments of the present application, a preparation method of the above composite material is provided. As Figure 1 shown, it includes the following steps:

[0052] S01. Provide luminescent quantum dots, non-luminescent quantum dots, a linking ligand, and an acid;

[0053] S02. Mix the luminescent quantum dots, non-luminescent quantum dots, acid, and linking ligand in a solvent to obtain the composite material.

[0054] Among them, the types, dosages, and effects of the luminescent quantum dots, non-luminescent quantum dots, and linking ligand in step S01 refer to the luminescent quantum dots, non-luminescent quantum dots, and linking ligand in the above composite material, and should have the same types, dosages, and effects.

[0055] The acid is used to eliminate the defect states on the surfaces of the luminescent quantum dots and non-luminescent quantum dots to promote the linking ligand to link the luminescent quantum dots and non-luminescent quantum dots respectively, thereby effectively linking the luminescent quantum dots and non-luminescent quantum dots. The acid includes but is not limited to organic acids and inorganic acids. In some embodiments, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid, and these inorganic acids have better effects in eliminating the defect states on the surface of the quantum dots. In further embodiments, the molar ratio of the acid to the total of the luminescent quantum dots and non-luminescent quantum dots is (0.1 - 2):10. In specific embodiments, the molar ratio of the acid to the total of the luminescent quantum dots and non-luminescent quantum dots is 0.1:10, 1:70, 0.2:10, 0.4:10, 0.6:10, 2.5:36, 1:10, 3:21, 1.6:10, 1.8:10 or 2:10.

[0056] In step S02, the luminescent quantum dots, non-luminescent quantum dots, acid, and linking ligand are mixed in a solvent so that the linking ligand links the luminescent quantum dots and non-luminescent quantum dots, thereby obtaining the above composite material.

[0057] In some embodiments, the preparation method of the composite material is also as Figure 2 shown. Among them, the step of mixing the luminescent quantum dots, non-luminescent quantum dots, acid, and linking ligand in a solvent includes:

[0058] S021. Add luminescent quantum dots, an acid, and a linking ligand to a solvent, and mix and stir at 80°C - 200°C for 10 minutes to 12 hours to obtain a first solution;

[0059] S022. Add non-luminescent quantum dots to the first solution, and mix and stir at 80°C - 200°C for 10 minutes to 12 hours.

[0060] Based on the above-mentioned linking ligand being mercaptoalkanoic acid, the method of first mixing and stirring the luminescent quantum dots, the acid, and the linking ligand and then adding the non-luminescent quantum dots enables the thiol group with stronger coordination ability in the linking ligand to preferentially coordinate with the metal atoms on the surface of the luminescent quantum dots, and the carboxyl group with weaker coordination ability coordinates with the metal atoms on the surface of the non-luminescent quantum dots, thereby effectively connecting the luminescent quantum dots and the non-luminescent quantum dots. At the same time, by adjusting the temperature and time of mixing and stirring within the above range, while promoting the effective connection of the linking ligand to the luminescent quantum dots and the non-luminescent quantum dots, the reaction efficiency can be effectively improved.

[0061] Based on the previous embodiment, the above-mentioned luminescent quantum dots are two-dimensional nanometer quantum dots. At this time, the non-luminescent quantum dots can be zero-dimensional quantum dots or two-dimensional nanometer quantum dots. In some embodiments, the non-luminescent quantum dots are zero-dimensional quantum dots. The two-dimensional nanometer quantum dots are heavier in mass than the zero-dimensional quantum dots. Combining the thiol group with strong coordination ability with the relatively heavier luminescent quantum dots and combining the carboxyl group with weaker coordination ability with the relatively lighter non-luminescent quantum dots can effectively prevent the quantum dots from falling off the linking ligand and ensure good stability of the composite material.

[0062] Among them, the solvent is preferably a non-polar solvent so that the luminescent quantum dots and the non-luminescent quantum dots have good dispersion performance in the solution. In some embodiments, the solvent is selected from at least one of chloroform, chlorobenzene, toluene, n-hexane, cyclohexane, n-octane, and n-butane.

[0063] In step S022, after mixing and stirring at 80°C - 200°C for 10 minutes to 12 hours, a second mixed solution is obtained, and the above-mentioned composite material is dispersed in the second mixed solution.

[0064] To facilitate the collection of the composite material in the second solution, after mixing and treating the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in the solvent, solid-liquid separation of the second solution is also included. In some embodiments, after the step of mixing and treating the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in the solvent, a precipitant is added to the product of the mixing treatment to precipitate the target product. In some embodiments, after the step of mixing and treating the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in the solvent, the product of the mixing treatment is subjected to annealing treatment.

[0065] Based on the above technical solutions, in the third aspect of the embodiments of the present application, a light-emitting diode is provided. As Figure 3 shown, the light-emitting diode includes: an anode 1, a light-emitting layer 3, and a cathode 5. Among them, the anode 1 and the cathode 5 are disposed opposite to each other, and the light-emitting layer 3 is disposed between the anode 1 and the cathode 5. In addition, the material of the light-emitting layer 3 includes: the aforementioned composite material, or the composite material prepared by the above preparation method.

[0066] The thickness of the light-emitting layer can refer to the conventional thickness in the art. In some embodiments, the thickness of the light-emitting layer is 5-100 nanometers.

[0067] The structure of the light-emitting diode of the present application can refer to the conventional technology in the art. In some embodiments, the light-emitting diode is a normal structure, and the anode is connected to the substrate as the bottom electrode; in other embodiments, the light-emitting diode is an inverted structure, and the cathode is connected to the substrate as the bottom electrode. Further, in addition to the above basic functional film layers such as the cathode, anode, and light-emitting layer, hole functional layers such as a hole injection layer, a hole transport layer, and a hole blocking layer can be provided between the anode and the light-emitting layer, and electron functional layers such as an electron injection layer, an electron transport layer, and an electron blocking layer can be provided between the light-emitting layer and the cathode.

[0068] In some embodiments, as Figure 4 shown, the light-emitting diode includes: 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. Among them, the anode 1 is connected to the substrate as the bottom electrode, the hole injection layer 21 is disposed between the anode 1 and the light-emitting layer 3, the hole transport layer 22 is disposed between the hole injection layer 21 and the light-emitting layer 3, and the electron transport layer 4 is disposed between the light-emitting layer 3 and the cathode 5.

[0069] In this light-emitting diode, the materials and thicknesses of the anode, hole injection layer, hole transport layer, light-emitting layer, electron transport layer, and cathode can refer to the conventional technology in the art.

[0070] The substrate includes a rigid substrate and a flexible substrate. In some embodiments, the substrate is selected from at least one of glass, silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.

[0071] 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, gold, etc. or their alloys, and 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, etc.

[0072] The material of the hole injection layer is selected as a material with 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), doped or undoped transition metal oxides, doped or undoped metal chalcogenides, etc.; among them, the transition metal oxides include but not limited to MoO3, VO2, WO3, CuO, etc., and the metal chalcogenides include but not limited to MoS2, MoSe2, WS2, WSe2, CuS, etc. The thickness of the hole injection layer is preferably 10-150 nm.

[0073] The material of the hole transport layer is selected as an organic material with good hole transport ability, 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)benzidine) (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'-bis(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.

[0074] 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.

[0075] The cathode can be selected as a single metal or its alloy, 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.

[0076] To enable those skilled in the art to clearly understand the above-mentioned implementation details and operations of this application, and to significantly demonstrate the advanced performance of the composite material and its preparation method in the embodiments of this application, the implementation of this application will be illustrated by examples below.

[0077] Example 1

[0078] In this example, a composite material is prepared using CdSe / CdS two-dimensional nano quantum dots, CdS quantum dots, and 11-mercaptoundecanoic acid as raw materials. The specific preparation method is as follows:

[0079] 1) The luminescent quantum dots are selected as CdSe / CdS two-dimensional nano quantum dots with an emission peak wavelength of 511 nm, a length of 30 nm, a width of 3 nm, a thickness of 2 nm, and a solution quantum yield of 80%.

[0080] The luminescent quantum dots, 20% hydrochloric acid, and 11-mercaptoundecanoic acid are added to n-hexane and mixed and stirred at 80 °C for 30 mins to obtain a first mixed solution. Among them, the mixed molar ratio of the luminescent quantum dots and 11-mercaptoundecanoic acid in the first mixed solution is 1:5; the molar ratio of hydrochloric acid to the luminescent quantum dots is 3:1.

[0081] 2) The non-luminescent quantum dots are selected as CdS quantum dots with a particle size of 5 nm. The non-luminescent quantum dots are added to the first mixed solution prepared in step 1) and mixed and stirred at 100 °C for 60 mins to obtain a second mixed solution. The composite material is dispersed in the second mixed solution, and the mixed mass ratio of the non-luminescent quantum dots and the luminescent quantum dots is 20:1.

[0082] After the stirring is completed, n-hexane is added to the product of the mixed stirring, and then ethyl acetate and ethanol are added to precipitate the composite material. After centrifugation and drying, the dried product is configured into a composite material solution with a mass concentration of 20 mg / mL.

[0083] 3) The composite material solution in step 2) is spin-coated on a quartz glass sheet to form a film.

[0084] Example 2

[0085] The preparation method of this example is basically the same as that of Example 1, and the main differences are: the linking ligand is selected as 5-mercaptopentanoic acid; the mixed molar ratio of the luminescent quantum dots and 5-mercaptopentanoic acid in the first mixed solution is 1:10; the mixed mass ratio of the non-luminescent quantum dots and the luminescent quantum dots in the second mixed solution is 30:1.

[0086] Example 3

[0087] The preparation method of this example is basically the same as that of Example 1, and the main differences are as follows: the linking ligand is selected as 8-mercaptooctanoic acid; the mixing molar ratio of the luminescent quantum dots and 8-mercaptooctanoic acid in the first mixed solution is 1:20; the molar ratio of hydrochloric acid to the luminescent quantum dots is 2.5:1; the mixing mass ratio of the non-luminescent quantum dots and the luminescent quantum dots in the second mixed solution is 35:1.

[0088] Example 4

[0089] The preparation method of this example is basically the same as that of Example 1, and the main differences are as follows: the linking ligand is selected as 7-mercaptoheptanoic acid; the mixing molar ratio of the luminescent quantum dots and 7-mercaptoheptanoic acid in the first mixed solution is 1:50; the molar ratio of hydrochloric acid to the luminescent quantum dots is 1:10; the mixing mass ratio of the non-luminescent quantum dots and the luminescent quantum dots in the second mixed solution is 60:1.

[0090] Comparative Example 1

[0091] In this comparative example, a thin film was prepared from CdSe / CdS two-dimensional nano quantum dots, and the specific preparation method is as follows:

[0092] 1) The quantum dots were selected as CdSe / CdS two-dimensional nano quantum dots with an emission peak wavelength of 511 nm, a length of 30 nm, a width of 3 nm, a thickness of 2 nm, and a solution quantum yield of 80%;

[0093] 2) The quantum dots were dispersed in n-octane and mixed thoroughly to form a quantum dot solution with a mass concentration of 20 mg / mL;

[0094] 3) The quantum dot solution prepared in step 2) was spin-coated on a quartz glass sheet to form a thin film.

[0095] Example 5

[0096] This example provides a light-emitting diode, and its preparation method includes: successively 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. Among them, the substrate is a glass substrate; the bottom electrode is ITO with a thickness of 100 nm; the hole injection layer is PEDOT:PSS with a thickness of 40 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 100 nm; the electron transport layer is ZnO with a thickness of 40 nm; the top electrode is Al with a thickness of 50 nm.

[0097] Example 6

[0098] The preparation method of this example is basically the same as that of Example 5, and the main difference is that: the light-emitting layer is the thin film prepared in Example 2.

[0099] Example 7

[0100] The preparation method of this example is basically the same as that of Example 5, and the main difference is that the light-emitting layer is the thin film prepared in Example 3.

[0101] Example 8

[0102] The preparation method of this example is basically the same as that of Example 5, and the main difference is that the light-emitting layer is the thin film prepared in Example 4.

[0103] Comparative Example 2

[0104] The preparation method of this comparative example is basically the same as that of Example 5, and the main difference is that the light-emitting layer is the thin film prepared in Comparative Example 1.

[0105] Take the thin films prepared in Examples 1-4 and Comparative Example 1 for quantum yield testing. Use the Edinburgh FLS980 fluorescence spectrometer combined with a photoluminescence quantum yield accessory to detect the quantum yield of the thin film samples, and obtain the results in Table 1.

[0106] Table 1

[0107] Comparative Example 1 Example 1 Example 2 Example 3 Example 4 Film Quantum Yield 20％ 34％ 40％ 31％ 33％

[0108] Take the light-emitting diodes prepared in Examples 5-8, and use an EQE optical test instrument to detect the external quantum dot efficiency (EQE) of each light-emitting diode. The detection results are shown in Table 2.

[0109] Among them, the ratio of the number of electron-hole pairs injected into the quantum dots converted into the number of emitted photons, with the unit of %, is an important parameter to measure the quality of electroluminescent devices. The specific calculation formula of EQE is as follows:

[0110]

[0111] In the formula, η e is the light output coupling efficiency, η r is the ratio of the number of recombined carriers to the number of injected carriers, χ is the ratio of the number of excitons generating photons to the total number of excitons, K R is the radiation process rate, K NR is the non-radiation process rate.

[0112] Table 2

[0113] Comparative Example 2 Example 5 Example 6 Example 7 Example 8 EQE (%) 1.3 2.5 3.1 3.8 3.9

[0114] It should be understood that the above examples and comparative examples are all illustrative, and the present application is not limited by the type of light-emitting diodes. For example, whether the light-emitting diode is a normal type, an inverted type, a top-emitting type or a bottom-emitting type, etc., the results are similar.

[0115] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A composite material, characterized in that, It is composed of luminescent quantum dots, non-luminescent quantum dots and linking ligands. The non-luminescent quantum dots surface-modify the luminescent quantum dots through the linking ligands. Among them, the luminescent quantum dots are two-dimensional nanometer quantum dots, the non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nanometer quantum dots, the shell material of the luminescent quantum dots is a II-VI group semiconductor material, the core material of the luminescent quantum dots is a II-VI group semiconductor material or a III-V group semiconductor material. The II-VI group semiconductor materials are 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, HgZnSTe. The III-V group semiconductor materials are 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, InAlPSb. The material of the non-luminescent quantum dots is the II-VI group semiconductor material. The linking ligands are selected from one of 5-mercaptovaleric acid, 8-mercaptooctanoic acid, 7-mercaptoheptanoic acid or 11-mercaptoundecanoic acid.

2. The composite material according to claim 1, characterized in that, The luminescent quantum dots have a core-shell structure, and the shell of the luminescent quantum dots grows along its planar direction.

3. The composite material according to claim 1, characterized in that, The non-luminescent quantum dots are connected to two planes in the thickness direction of the luminescent quantum dots.

4. The composite material according to claim 3, wherein, The non-luminescent quantum dots are non-core-shell structure quantum dots; The metal element of the non-luminescent quantum dots is in the same group as the metal element of the shell of the luminescent quantum dots, and / or the non-metal element of the non-luminescent quantum dots is in the same group as the non-metal element of the shell of the luminescent quantum dots.

5. The composite material according to any one of claims 1 to 4, characterized in that, The mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1:(10 - 100); and / or The molar ratio of the luminescent quantum dots to the linking ligands is 1:(1 - 100).

6. A method for preparing a composite material, characterized in that, It includes the following steps: Provide luminescent quantum dots, non-luminescent quantum dots, a linking ligand, and an acid; wherein, first add the luminescent quantum dots, the acid, and the linking ligand into a solvent and mix and stir them, then add the non-luminescent quantum dots to obtain the composite material. The definitions of the luminescent quantum dots, the non-luminescent quantum dots, and the linking ligand are as described in claim 1. The acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid.

7. The preparation method according to claim 6, characterized in that, The step of mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand in a solvent includes: Add the luminescent quantum dots, the acid, and the linking ligand into a solvent, mix and stir at 80°C - 200°C for 10 minutes to 12 hours to obtain a first solution; Add the non-luminescent quantum dots into the first solution, and mix and stir at 80°C - 200°C for 10 minutes to 12 hours.

8. The preparation method according to claim 7, wherein, The luminescent quantum dots are two-dimensional nano quantum dots.

9. The preparation method according to claim 7, characterized in that, The non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nano quantum dots.

10. The preparation method according to claim 7, characterized in that, The molar ratio of the acid to the sum of the luminescent quantum dots and the non-luminescent quantum dots is (0.1 - 2) :

10.

11. The preparation method according to claim 7, characterized in that, The mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1 : (10 - 100).

12. The preparation method according to claim 7, wherein, The linking ligand is selected from mercaptoalkanoic acids, and the molar ratio of the luminescent quantum dots to the linking ligand is 1 : (1 - 100).

13. The preparation method according to claim 7, characterized in that, The solvent is selected from at least one of chloroform, chlorobenzene, toluene, n-hexane, cyclohexane, n-octane, and n-butane.

14. A light-emitting diode includes a light-emitting layer, and the material of the light-emitting layer includes: The composite material according to any one of claims 1 to 5 or the composite material prepared by the preparation method according to any one of claims 6 to 13.

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