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

Abstract

The invention discloses a composite material, a preparation method thereof and a quantum dot light-emitting device, the composite material comprises a first quantum dot and a second quantum dot, the surface of the first quantum dot is connected with an anionic group, and the surface of the second quantum dot is connected with a cationic group. The composite material can improve the luminescence performance of the quantum dot luminescent device.

Description

Technical Field

[0001] The present application relates to the field of display technologies, and in particular, to a composite material, a preparation method thereof, and a quantum dot light-emitting device. Background Art

[0002] Currently, the widely used light-emitting devices are organic light-emitting devices (OLEDs) and quantum dot light-emitting devices (QLEDs). QLEDs have the advantages of saturated emission light color, adjustable wavelength, low turn-on voltage, good solution processability, easy fine control of quantum dots, etc., and have high photoluminescence and electroluminescence quantum yields. In recent years, they have become strong competitors of OLEDs.

[0003] The structure of a traditional QLED device generally includes an anode, a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, an electron injection layer, and a cathode. Under the action of an electric field, the holes generated by the anode and the electrons generated by the cathode of the light-emitting device move, are respectively injected into the hole transport layer and the electron transport layer, and finally migrate to the light-emitting layer. When the two meet in the light-emitting layer, energy excitons are generated, which excite the light-emitting molecules to finally generate visible light.

[0004] In existing QLED light-emitting devices, since the surface of the quantum dot material forming the light-emitting layer is usually connected with organic ligands, and the organic ligands are insulating, the potential barrier between quantum dots is relatively high, which limits the transport of carriers inside the light-emitting layer, and further leads to poor light-emitting performance of QLEDs. Summary of the Invention

[0005] In view of this, the present application provides a light-emitting device, aiming to improve the problem of poor stability of the light-emitting performance of existing quantum dot light-emitting devices.

[0006] In a first aspect, an embodiment of the present application provides a composite material, which includes a first quantum dot and a second quantum dot. Among them, an anion group is connected to the surface of the first quantum dot, and a cation group is connected to the surface of the second quantum dot.

[0007] Optionally, in some embodiments of the present application, the element forming the anion group includes one of S, Se, Te, and P;

[0008] and / or, the element forming the cation group includes one of Cd, Zn, Pb, Hg, and In;

[0009] Optionally, the material of the second quantum dot includes at least one metal element, and the element forming the cation group is selected from the metal elements in the material of the second quantum dot;

[0010] And / or, the number of charges of the anionic group is the same as that of the cationic group or the ratio of the number of charges of the anionic group to the number of charges of the cationic group is 0.8 to 1.2.

[0011] Optionally, in some embodiments of the present application, the chemical formula of the first quantum dot is represented as QDs / S 2- , and the chemical formula of the second quantum dot is represented as QDs / M 2+ .

[0012] Optionally, in some embodiments of the present application, both the first quantum dot and the second quantum dot are core-shell quantum dots. In the first quantum dot, the anionic group is connected to the outer layer of its shell;

[0013] And / or, in the second quantum dot, the cationic group is connected to the outer layer of its shell.

[0014] Optionally, in some embodiments of the present application, the composite material includes a first type of quantum dot having a first core-shell structure, a second type of quantum dot having a second core-shell structure, and a third type of quantum dot having a third core-shell structure, wherein the first core-shell structure is configured as a non-hole confinement structure, the second core-shell structure is configured as a non-electron confinement structure, and the third core-shell structure is configured as a type-I electron and hole confinement structure;

[0015] Wherein, both the first quantum dot and the second quantum dot are configured as the first type of quantum dot having the first core-shell structure, such that the composite material is configured to facilitate hole injection;

[0016] Or, one of the first quantum dot and the second quantum dot is configured as the first type of quantum dot having the first core-shell structure, and the other of the first quantum dot and the second quantum dot is configured as the third type of quantum dot having the third core-shell structure, such that the composite material is configured to facilitate hole injection;

[0017] Or, both the first quantum dot and the second quantum dot are configured as the second type of quantum dot having the second core-shell structure, such that the composite material is configured to facilitate electron injection;

[0018] Or, one of the first quantum dot and the second quantum dot is configured as the second type of quantum dot having the second core-shell structure, and the other of the first quantum dot and the second quantum dot is configured as the third type of quantum dot having the third core-shell structure, such that the nanomaterial is configured to facilitate electron injection;

[0019] Or, both the first quantum dot and the second quantum dot are configured as the third type of quantum dot having the third core-shell structure, such that the quantum dot is configured to facilitate balanced transport of holes and electrons;

[0020] Alternatively, one of the first quantum dot and the second quantum dot includes a first type of quantum dot having a first core-shell structure, and the other of the first quantum dot and the second quantum dot is configured as a second type of quantum dot having a second core-shell structure, such that the quantum dots are configured to facilitate balanced hole and electron transport;

[0021] Alternatively, the first quantum dot includes a first type of quantum dot having a first core-shell structure, a second type of quantum dot having a second core-shell structure, and a third type of quantum dot having a third core-shell structure, and the second quantum dot includes a first type of quantum dot having a first core-shell structure, a second type of quantum dot having a second core-shell structure, and a third type of quantum dot having a third core-shell structure, such that the quantum dots are configured to facilitate balanced hole and electron transport.

[0022] Optionally, in some embodiments of the present application, the average particle size of the first quantum dot is 5 nm to 25 nm;

[0023] and / or, the average particle size of the second quantum dot is 5 nm to 25 nm;

[0024] And / or, the first quantum dot and the second quantum dot each independently include one or more of a single-structure quantum dot, a core-shell structure quantum dot, and a perovskite semiconductor material. Among them, the material of the single-structure quantum dot, the core material of the core-shell structure quantum dot, and the shell material of the core-shell structure quantum dot may each independently include one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds include one or more of 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. The IV-VI group compounds include one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds include one or more of 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. The I-III-VI group compounds include one or more of CuInS2, CuInSe2, and AgInS2. The perovskite semiconductor material includes a doped or undoped inorganic perovskite semiconductor or an organic-inorganic hybrid perovskite semiconductor. The structural general formula of the inorganic perovskite semiconductor is AMX3, where A is a Cs + ion, M is a divalent metal cation, including Pb 2+ 、Sn 2+, Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2 + , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following, the structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following.

[0025] In a second aspect, the embodiments of the present application further provide a method for preparing a composite material, including the following steps:

[0026] Provide a third quantum dot solution including third quantum dots, where the third quantum dot solution includes a first organic solvent and first quantum dots dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dots;

[0027] Provide an anion ligand solution including an anion group, where the anion ligand solution includes a second organic solvent and an anion ligand dispersed in the second organic solvent;

[0028] Mix the third quantum dot solution with the anion ligand solution, and the anion group performs ligand exchange with the first ligand to obtain first quantum dots, and an anion group is connected to the surface of the first quantum dots;

[0029] Disperse the first quantum dots in a second organic solvent to obtain a first quantum dot solution;

[0030] Provide a cationic ligand solution including a cationic group, where the cationic ligand solution includes a third organic solvent and a cationic ligand dispersed in the third organic solvent;

[0031] Mix the first quantum dot solution with the cationic ligand solution, and perform ligand exchange between the cationic group and the anionic group to obtain second quantum dots, and the surface of the second quantum dots is connected with a cationic group;

[0032] Disperse the second quantum dots in a second organic solvent to obtain a second quantum dot solution;

[0033] Mix the first quantum dot solution with the second quantum dot solution to obtain the composite material.

[0034] In a third aspect, an embodiment of the present application further provides a method for preparing a composite material, including the following steps:

[0035] Provide a third quantum dot solution including third quantum dots, where the third quantum dot solution includes a first organic solvent and third quantum dots dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dots;

[0036] Provide a fourth quantum dot solution including fourth quantum dots, where the fourth quantum dot solution includes a first organic solvent and fourth quantum dots dispersed in the first organic solvent, and a second ligand is connected to the surface of the fourth quantum dots;

[0037] Provide an anionic ligand solution including an anionic group, where the anionic ligand solution includes a second organic solvent and an anionic ligand dispersed in the second organic solvent;

[0038] Mix the third quantum dot solution with the anionic ligand solution, and perform ligand exchange between the anionic group and the first ligand to obtain first quantum dots, and an anionic group is connected to the surface of the first quantum dots, and disperse the first quantum dots in the second organic solvent to obtain a first quantum dot solution;

[0039] Mix the fourth quantum dot solution with the anionic ligand solution, and perform ligand exchange between the anionic group and the second ligand to obtain fifth quantum dots, and an anionic group is connected to the surface of the fifth quantum dots, and disperse the fifth quantum dots in the second organic solvent to obtain a fifth quantum dot solution;

[0040] Provided is a cationic ligand solution including a cationic group, the cationic ligand solution including a third organic solvent and a cationic ligand dispersed in the third organic solvent;

[0041] Mix the fifth quantum dot solution with the cationic ligand solution, and perform ligand exchange between the cationic group and the anionic group to obtain a second quantum dot, wherein the surface of the second quantum dot is connected with a cationic group, and disperse the second quantum dot in the second organic solvent to obtain a second quantum dot solution;

[0042] Mix the first quantum dot solution with the second quantum dot solution to obtain the composite material.

[0043] Optionally, in some embodiments, the anionic ligand includes Na2S or (NH4)2S;

[0044] And / or, the cationic ligand includes a soluble metal salt, and the metal element in the soluble metal salt includes one of Cd, Zn, Pb, Hg, and In.

[0045] Optionally, in some embodiments, the first organic solvent includes an alkane with 6 - 18 carbon atoms;

[0046] And / or, the second organic solvent includes NMF, DMSO, MEK, ACN or a thiol organic solvent;

[0047] And / or, the third organic solvent includes NMF, DMSO, MEK or ACN;

[0048] And / or, the first ligand includes capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, stearic acid, octanethiol, dodecyl mercaptan, octadecyl mercaptan, oleylamine, octadecylamine, octylamine, dioctylamine, trioctylamine, tri-n-octylphosphine or tri-n-octylphosphine oxide;

[0049] And / or, the second ligand includes capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, stearic acid, octanethiol, dodecyl mercaptan, octadecyl mercaptan, oleylamine, octadecylamine, octylamine, dioctylamine, trioctylamine, tri-n-octylphosphine or tri-n-octylphosphine oxide.

[0050] Fourthly, an embodiment of the present application further provides a quantum dot light-emitting device, including an anode, a cathode and a light-emitting layer located between the anode and the cathode, and the nanomaterial forming the light-emitting layer includes the above composite material, or the composite material forming the light-emitting layer is prepared by the above preparation method.

[0051] The composite material provided by this application includes a first quantum dot and a second quantum dot, where the first quantum dot carries an anionic group and the second quantum dot carries a cationic group. The above composite material can improve the luminescence performance of the quantum dot light-emitting device. Description of the Drawings

[0052] In order to more clearly illustrate the technical solutions in the embodiments of this application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of this application. For those skilled in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0053] Figure 1 is a schematic structural diagram of a quantum dot light-emitting device provided by an embodiment of this application;

[0054] Figure 2 is a schematic structural diagram of a quantum dot light-emitting device provided by another embodiment of this application;

[0055] Figure 3 is a schematic diagram of the process of anionic ligand exchange of quantum dots provided by an embodiment of this application;

[0056] Figure 4 is a schematic diagram of the assembly process of the quantum dot fusion unit provided by an embodiment of this application. Detailed Embodiments

[0057] The following will clearly and completely describe the technical solutions in the embodiments of this application with reference to the drawings in the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, rather than all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative efforts belong to the scope of protection of this application. In addition, it should be understood that the specific embodiments described herein are only used to illustrate and explain this application, and are not used to limit this application.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this invention belongs. The terms used in the description of this invention in this specification are only for the purpose of describing specific embodiments, and are not intended to limit this invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0059] In this application, unless otherwise specified, the orientation terms such as "upper" and "lower" generally refer to the upper and lower directions in the actual use or working state of the device, specifically the drawing directions in the attached drawings; while "inner" and "outer" refer to the outline of the device. In addition, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc. are only used as labels without imposing numerical requirements or establishing an order.

[0060] In this application, "and / or" describes the association relationship of associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone. Where A and B can be singular or plural.

[0061] In this application, "at least one" means one or more, and "multiple" means two or more. "One or more kinds", "at least one of the following (items)" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can both represent: a, b, c, a - b (that is, a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0062] In this application, when forming another layer "on" a certain layer, the so-called "on" is a broad concept, which can mean that the formed another layer is adjacent to a certain layer, or there are other spacer structure layers between another layer and a certain layer. For example, when forming a second electrode "on" the first carrier functional layer, the so-called "on" can mean that the formed second electrode is adjacent to the first carrier functional layer, or there are other spacer structure layers between the second electrode and the first carrier functional layer, such as a light-emitting layer.

[0063] The various embodiments of this application can exist in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity and should not be construed as a rigid limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and the single values within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and the single numbers within that range, such as 1, 2, 3, 4, 5, and 6, which applies regardless of the range. In addition, whenever a numerical range is indicated herein, it means including any cited number (fraction or integer) within the indicated range.

[0064] In the first aspect, please refer to Figure 1, embodiments of the present application provide a quantum dot light-emitting device 100. The quantum dot light-emitting device includes an anode 10, a light-emitting layer 20, and a cathode 30 stacked in sequence, and the light-emitting layer 20 is located between the anode 10 and the cathode 30.

[0065] In one embodiment, the quantum dot light-emitting device 100 further includes a hole transport layer 40 located between the anode 10 and the light-emitting layer 20. In other words, the light-emitting device 100 includes an anode 10, a hole transport layer 40, a light-emitting layer 20, and a cathode 30 stacked in sequence.

[0066] In one embodiment, the quantum dot light-emitting device 100 further includes an electron transport layer 50 located between the light-emitting layer 20 and the cathode 30. In other words, the light-emitting device 100 includes an anode 10, a hole transport layer 40, a light-emitting layer 20, an electron transport layer 50, and a cathode 30 stacked in sequence.

[0067] In one embodiment, the quantum dot light-emitting device 100 further includes a hole injection layer 60 located between the anode 10 and the hole transport layer 40. In other words, the quantum dot light-emitting device 100 includes an anode 10, a hole injection layer 60, a hole transport layer 40, a light-emitting layer 20, an electron transport layer 50, and a cathode 30 stacked in sequence.

[0068] In one embodiment, the quantum dot light-emitting device 100 further includes a substrate 70. The substrate 70 can be a rigid substrate or a flexible substrate, and the specific materials for forming the substrate 70 can include at least one of glass, silicon wafer, polycarbonate, polymethyl methacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.

[0069] In a further embodiment, the quantum dot light-emitting device 100 can be a normal structure or an inverted structure.

[0070] As Figure 1 shown, a schematic structural diagram of a quantum dot light-emitting device 100 with a normal structure is provided. The quantum dot light-emitting device 100 includes a substrate 70, an anode 10 located on the upper surface of the substrate 70, a hole injection layer 60 located on the upper surface of the anode 10, a hole transport layer 40 located on the upper surface of the hole injection layer 60, a light-emitting layer 20 located on the upper surface of the hole transport layer 40, an electron transport layer 50 located on the upper surface of the light-emitting layer 20, and a cathode 30 located on the upper surface of the electron transport layer 50.

[0071] As Figure 2The following provides a schematic structural diagram of a quantum dot light-emitting device 100 with an inverted structure. The quantum dot light-emitting device 100 includes a substrate 70, a cathode 30 located on the upper surface of the substrate 70, an electron transport layer 50 located on the upper surface of the cathode 30, a light-emitting layer 20 located on the upper surface of the electron transport layer 50, a hole transport layer 40 located on the upper surface of the light-emitting layer 20, a hole injection layer 60 located on the upper surface of the hole transport layer 40, and an anode 10 located on the upper surface of the hole injection layer 60.

[0072] In some preferred embodiments, the anode 10 is selected from one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, and carbon nanotubes; the hole injection layer 60 uses a common aqueous PEDOT:PSS solution; the material of the hole transport layer 40 is one or more of PVK (polystyrene-based compound), Poly-TPD (poly-N,N'-diphenyl-N,N'-dimethylaniline), CBP (2,2'-bis(1,3-benzothiadiazolyl)biphenyl), TCTA (4,4',4''-tris(fluoren-2,7-yl)triphenylamine), and TFB (2,2',7,7'-tetrakis(N,N-di(4-cresylphenyl ethyl)-9,9'-octylinden)fluorene); the light-emitting layer 20 includes a red quantum dot light-emitting layer or a green quantum dot light-emitting layer or a blue quantum dot light-emitting layer; the material of the electron transport layer 50 is n-type ZnO and doped with one or more of Al, Mg, Ga, and Sn; the cathode 30 is selected from one or more of Al, Ca, Ba, and Ag.

[0073] Due to its unique optoelectronic properties, quantum dot light-emitting devices (QLEDs) can be applied to the lighting and display industries. However, the stability and working life of quantum dot light-emitting devices are still key issues facing the commercial application of QLEDs. One of the key problems affecting the working stability and light-emitting performance of quantum dot light-emitting devices is the imbalance in carrier injection in quantum dot light-emitting devices, that is, there are multi-hole quantum dot light-emitting devices or multi-electron quantum dot light-emitting devices. In multi-hole quantum dot light-emitting devices, excessive holes will cause rapid degradation of the quantum dot light-emitting device and lead to permanent degradation of the quantum dot light-emitting device. In multi-electron quantum dot light-emitting devices, excessive electrons will cause a decrease in carrier injection efficiency and lead to the degradation problem of the light-emitting device.

[0074] In related technologies, in order to improve the working performance of quantum dot light-emitting devices, the balance of charges in quantum dot light-emitting devices is achieved by reducing electron injection. For example, an electron blocking layer is provided between the light-emitting layer and the electron transport layer. The materials used for the electron blocking layer include polymethyl methacrylate (PMMA), polyethyleneimine (PEI), alumina, and Cs2CO3, etc. However, with the incorporation of the electron blocking layer in quantum dot light-emitting devices, the internal resistance of quantum dot light-emitting devices increases, which is not conducive to further improving the performance of QLED devices.

[0075] In the research on improving the working performance of quantum dot light-emitting devices, the inventor found that it is relatively difficult to control the carrier injection balance of quantum dot light-emitting devices by using less hole transport layer material and electron transport layer material. At the same time, due to the energy level position differences of the quantum dot materials in different light-emitting layers, it is very difficult to effectively control the carrier injection balance solely by changing the selection of quantum dot materials. Therefore, adjusting the relative injection levels of electrons and holes by changing the structure of the composite material forming the light-emitting layer is crucial for achieving carrier balance in quantum dot light-emitting devices.

[0076] In a second aspect, an embodiment of the present application provides a composite material for forming the above-mentioned light-emitting layer. In the embodiment of the present application, the light-emitting layer is described by using a composite material with a core-shell structure. The quantum dot includes a core and at least one shell located outside the core. An organic ligand is also connected to the outer surface of the shell of the quantum dot. The core material of the quantum dot is used for light emission, and the shell layer material is used to form a passivation shell layer with a wide bandgap, thereby enhancing the structural stability of the quantum dot. The organic ligand modifies the outer surface of the quantum dot, thereby enhancing the stability and dispersibility of the quantum dot.

[0077] Both the core material and the shell layer material of the quantum dot can include binary alloys, multi-component alloys, or multi-component graded alloys composed of II-VI group, III-V group, or IV-VI group elements. As an example, the composite material with a core-shell structure can include, but is not limited to, one or more of CdSe / CdSeS / CdS, InP / ZnSeS / ZnS, CdZnSe / ZnSe / ZnS, CdSeS / ZnSeS / ZnS, CdSe / ZnS, CdSe / ZnSe / ZnS, ZnSe / ZnS, ZnSeTe / ZnS, CdSe / CdZnSeS / ZnS, and InP / ZnSe / ZnS.

[0078] In some embodiments, the core material of the quantum dot includes at least one of CdSe, CdS, CdTe, CdSeTe, CdZnS, PbSe, ZnTe, CdSeS, PbS, PbTe, HgS, HgSe, HgTe, GaP, GaAs, InP, InAs, InZnP, and InGaP; the outer shell material of the quantum dot includes one or more of CdS, CdTe, CdSeTe, CdZnSe, CdZnS, CdSeS, ZnSe, ZnSeS, ZnS, PbS, PbSeS, InZnP, and InGaP.

[0079] The organic ligands connected to the quantum dots include at least one of substituted or unsubstituted C6-C24 fatty acids, substituted or unsubstituted C6-C24 fatty amines, substituted or unsubstituted C6-C24 aliphatic thiols, substituted or unsubstituted C6-C24 aliphatic thioethers, substituted or unsubstituted C6-C24 aliphatic phosphines, substituted or unsubstituted C6-C24 aliphatic phosphine oxides, substituted or unsubstituted C8-C20 aliphatic phosphoric acids, substituted or unsubstituted C6-C24 aliphatic phosphates, substituted or unsubstituted C6-C24 aliphatic phosphites, and substituted or unsubstituted C6-C24 aliphatic phosphite esters, wherein the substituents of the substituted ones are selected from at least one of C1-C6 alkyl groups, C1-C6 alkoxy groups, and halogens;

[0080] Optionally, the substituted or unsubstituted C6-C24 fatty acids include at least one of capric acid, undecenoic acid, myristic acid, oleic acid, linoleic acid, and stearic acid;

[0081] Optionally, the substituted or unsubstituted C6-C24 aliphatic thiols include at least one of octanethiol, dodecyl mercaptan, and octadecyl mercaptan;

[0082] Optionally, the substituted or unsubstituted C6-C24 fatty amines include at least one of oleylamine, octadecylamine, octylamine, dioctylamine, and trioctylamine;

[0083] Optionally, the substituted or unsubstituted C6-C24 aliphatic phosphines include tri-n-octylphosphine (TOP);

[0084] Optionally, the substituted or unsubstituted C6-C24 aliphatic phosphine oxides include tri-n-octylphosphine oxide (TOPO).

[0085] In the embodiments of the present application, by optimizing the material combination structure of the quantum dots, the carrier injection balance of the quantum dot light-emitting device is further adjusted, and the instability of the quantum dot light-emitting device caused by the imbalance of carriers is further improved.

[0086] In a specific implementation, the composite material combination forming the light-emitting layer includes a first quantum dot and a second quantum dot, an anion group is connected to the surface of the first quantum dot, and a cation group is connected to the surface of the second quantum dot.

[0087] Through the electrostatic interaction between the first quantum dot and the second quantum dot, the interlayer potential barrier between the quantum dots can be reduced, which is beneficial to the internal transport of carriers in the light-emitting layer.

[0088] In some embodiments, the number of charges of the anionic group connected to the outer surface of the first quantum dot is configured to be the same as the number of charges of the cationic group connected to the outer surface of the second quantum dot, so that there is an electrostatic attraction between the first quantum dot and the second quantum dot for fusion assembly. Through the process of fusion assembly, the surface defect state of the quantum dot can be repaired, which is beneficial to improving the injection balance of carriers.

[0089] Alternatively, the ratio of the number of charges of the anionic group to the number of charges of the cationic group is 0.8 to 1.2. In some specific examples, the ratio of the number of charges of the anionic group to the number of charges of the cationic group can be 0.8, 0.9, 1.0, 1.1, 1.2, and the values between any two of the above or the ranges between any two of the above values.

[0090] Compared with the related art, an organic ligand is connected to the outer surface of the quantum dot in the core-shell structure. The organic ligand is usually insulating, making the light-emitting layer closer to an insulating layer, which is not conducive to the transport of carriers in the light-emitting layer. By connecting an anionic group or a cationic group to the outer surface of the quantum dot in the core-shell structure, the quantum dot group structure with the charged group is beneficial to reducing the interlayer potential barrier between the various layers of the quantum dot. The first quantum dot connected with the anionic group has a stronger hole attraction due to the higher negative charge density on its surface. The second quantum dot connected with the cationic group has a stronger electron attraction due to the higher positive charge density on its surface, thereby promoting the transport of carriers in the light-emitting layer, which is beneficial to improving the luminescence performance of the quantum dot light-emitting device.

[0091] In some embodiments, considering the functionalization requirements of the anionic group connected to the outer surface of the quantum dot, for example, the anionic group preferably has a small steric hindrance. The anionic group suitable for connecting to the surface of the quantum dot is configured as an anion composed of a single chemical element. The chemical element forming the anion preferably comes from non-metallic elements of Group V and Group VI. Suitable elements include S, Se, Te, and P, etc.

[0092] In a further preferred embodiment, considering the preparation process of the composite material, the chemical element suitable for forming the anionic group is S.

[0093] In some embodiments, the cationic group suitable for connecting to the surface of the quantum dot is configured as a cation composed of a single chemical element. The chemical element forming the cation includes a metal element or a transition metal element. Suitable elements include Cd, Zn, Pb, Hg, and In, etc.

[0094] In a further preferred embodiment, considering the preparation process of the composite material, the chemical element suitable for forming a cationic group is the same as one of the bulk materials of the quantum dots.

[0095] In some embodiments, the chemical formula of the above-mentioned first quantum dot is QDs / S 2- , that is, S is connected to the outer surface of the first quantum dot 2- , the chemical formula of the above-mentioned second quantum dot is QDs / M 2+ , two negative charges are connected to the outer surface of the first quantum dot, and two positive charges are connected to the outer surface of the second quantum dot. On the one hand, it is beneficial for the charged groups to form a smaller steric hindrance on the outer surface of the quantum dots, so as to facilitate the connection of multiple anionic groups or multiple cationic groups on the outer surface of the quantum dots. On the other hand, due to the fusion assembly of multiple anionic groups of the first quantum dot and multiple cationic groups of the second quantum dot, it is beneficial to repair the defects on the multiple outer surfaces of the first quantum dot connected with anionic groups, as well as to repair the defects on the multiple outer surfaces of the second quantum dot connected with cationic groups, and improve the injection efficiency of carriers.

[0096] The core-shell structured quantum dots are a kind of nanomaterials. The core-shell structured quantum dots include a core material and at least one shell material wrapping the core material. Its core material is usually a metal or semiconductor material, and this structure makes the quantum dots have special optoelectronic properties.

[0097] In the embodiments of the application, the band gap width (Eg) of the core-shell structured quantum dots is preferably 1.9 eV - 2.75 eV. Among them, when the band gap width Eg of the quantum dots is 1.9 eV - 2 eV, correspondingly, the quantum dot light-emitting device emits red light. When the band gap width Eg of the quantum dots is 2.25 eV - 2.38 eV, correspondingly, the quantum dot light-emitting device emits green light. When the band gap width Eg of the quantum dots is 2.58 eV - 2.75 eV, correspondingly, the quantum dot light-emitting device emits blue light.

[0098] In the core-shell structured quantum dots, the conduction band energy level difference and the valence band energy level difference are two important parameters describing the electron energy level distribution of the quantum dots, and are of great significance for the optoelectronic performance of the quantum dots.

[0099] In the embodiments of the present application, the bottom energy level of the conduction band of the core material is called E CB,核 , the bottom energy level of the conduction band of the shell material is called E CB,壳 , the conduction band energy level difference between the shell material and the core material is expressed as ΔE CB,壳-核 = E CB,壳 - E CB,核, the magnitude of the conduction band energy level difference represents the force of electron transfer between the core and the shell. When the conduction band energy level difference is large, electrons are more likely to transfer from the core to the shell, thereby enhancing the conductivity and photoelectric conversion efficiency of the quantum dots.

[0100] In the embodiments of the present application, the top energy level of the valence band of the core material is referred to as E VB,核 , and the top energy level of the valence band of the shell material is referred to as E VB,壳 , and the valence band energy level difference between the shell material and the core material is denoted as ΔE VB,壳-核 = E VB,壳 - E VB,核 , the magnitude of the valence band energy level difference represents the energy difference of electrons between the core material and the shell material. When the valence band energy level difference is large, the energy difference for electrons to jump from the core layer to the shell layer is large.

[0101] The magnitude of the conduction band energy level difference is related to factors such as the energy band structure, the energy levels of the materials, and the lattice matching between the core material and the shell material. In the embodiments of the present application, by finely adjusting the magnitude of the conduction band energy level difference between the core material and the shell material, fine adjustment of the electronic properties of the core-shell structured quantum dots is achieved.

[0102] The magnitude of the valence band energy level difference is related to factors such as the combination of the core material and the shell material, the thickness of the layer, and the crystallinity. In the embodiments of the present application, by finely adjusting the value of the valence band energy level difference of the quantum dots, the energy band structure and optical properties of the quantum dots are further adjusted.

[0103] The conduction band energy level difference and the valence band energy level difference of the above-mentioned core-shell structured quantum dots can both be obtained through experimental measurement techniques or theoretical algorithms.

[0104] In the embodiments of the present application, according to the different relative positions and arrangement modes of the energy bands of the core material and the shell material of the core-shell structured quantum dots, the quantum dots include the first type of quantum dots with the first core-shell structure, the second type of quantum dots with the second core-shell structure, and the third type of quantum dots with the third core-shell structure.

[0105] Among them, in the first type of quantum dots, the first core-shell structure is configured as a non-hole confinement structure, and the valence band energy level difference ΔE between the shell material and the core material of the quantum dots VB,壳-核 ≥ -0.2 eV, and the conduction band energy level difference ΔE between the shell material and the core material of the quantum dots CB,壳-核≥0.2 eV. Due to the large value of the valence band energy level difference between the core and shell of the quantum dots, holes can be delocalized within the core-shell of the quantum dots. And in the formed quantum dot thin film, there are many overlapping regions between the hole wave functions of quantum dots, which is conducive to the transport of holes between quantum dots. Therefore, using more of the first type of composite material inside the quantum dot light-emitting device is beneficial to improving the hole injection level of the quantum dot light-emitting device.

[0106] In the second type of quantum dots, the second core-shell structure is configured as a non-electron confinement structure, and the valence band energy level difference ΔE between the shell material and the core material of the quantum dots VB,壳-核 ≤ -0.2 eV, and the conduction band energy level difference ΔE between the shell material and the core material of the quantum dots CB,壳-核 ≤ 0.2 eV. Due to the small value of the valence band energy level difference of the shell material, electrons can be delocalized within the core-shell of the quantum dots. And in the formed quantum dot thin film, there are many overlapping regions between the electron wave functions of quantum dots, which is conducive to the transport of electrons between quantum dots. Therefore, using more of the second type of composite material inside the quantum dot light-emitting device is beneficial to improving the electron injection level of the quantum dot light-emitting device.

[0107] In the third type of quantum dots, the third core-shell structure is configured as a type-I electron confinement and hole confinement core-shell structure, and the valence band energy level difference ΔE between the shell material and the core material of the quantum dots VB,壳-核 ≤ -0.2 eV, and the conduction band energy level difference ΔE between the shell material and the core material of the quantum dots CB,壳-核 ≥ 0.2 eV. Among them, electrons and holes inside the quantum dots are both confined within the core range. Due to the difference in the carrier injection barriers between the quantum dots and the adjacent electron transport layer or between the quantum dots and the adjacent hole transport layer, there is an asymmetry in the transport barriers for electrons and holes.

[0108] Among them, the first type of quantum dots, the second type of quantum dots, and the third type of quantum dots are mainly based on the valence band energy level difference and the conduction band energy level difference between the shell material and the core material. Then, a suitable binary alloy or multi-component alloy is selected, and by adjusting the component content of each metal element in the binary alloy or multi-component alloy, the bandgap width and energy level position of the quantum dots are further adjusted. Thus, the first type of quantum dots have the characteristics of a non-hole confinement core-shell structure, the second type of quantum dots have the characteristics of a non-electron confinement core-shell structure, and the third type of quantum dots have the characteristics of a type-I electron confinement and hole confinement core-shell structure.

[0109] In the embodiments of the present application, by providing a composite material combination structure with different core-shell structures for different systems of quantum dot light-emitting devices, the injection balance of carriers is effectively promoted, and the working stability of the quantum dot light-emitting devices is improved.

[0110] In one embodiment, in a quantum dot light-emitting device of a multi-electron system, the composite material forming the light-emitting layer uses a first type of quantum dot with a non-hole-confining core-shell structure, wherein anionic groups are connected to the surfaces of a part of the first type of quantum dots, and cationic groups are connected to the surfaces of another part of the first type of quantum dots. The first type of quantum dots with anionic groups and the first type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer.

[0111] In an alternative embodiment, in a quantum dot light-emitting device of a multi-electron system, the composite material forming the light-emitting layer uses a combination of a first type of quantum dot with a non-hole-confining core-shell structure and a third type of quantum dot with a type-I electron-confining and hole-confining core-shell structure. Anionic groups are connected to the surfaces of one type of quantum dots among the first type of quantum dots and the third type of quantum dots, and cationic groups are connected to the surfaces of the other type of quantum dots among the first type of quantum dots and the third type of quantum dots. The first type of quantum dots with anionic groups and the third type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer, or the third type of quantum dots with anionic groups and the first type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer.

[0112] In one embodiment, in a quantum dot light-emitting device of a multi-hole system, the composite material forming the light-emitting layer uses a second type of quantum dot with a non-electron-confining core-shell structure, wherein anionic groups are connected to the surfaces of a part of the second type of quantum dots, and cationic groups are connected to the surfaces of another part of the second type of quantum dots. The second type of quantum dots with anionic groups and the second type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer.

[0113] In an alternative embodiment, in a quantum dot light-emitting device of a multi-hole system, the composite material forming the light-emitting layer uses a combination of a second type of quantum dot with a non-electron-confining core-shell structure and a third type of quantum dot with a type-I electron and hole-confining core-shell structure. Anionic groups are connected to the surfaces of one type of quantum dots among the second type of quantum dots and the third type of quantum dots, and cationic groups are connected to the surfaces of the other type of quantum dots among the second type of quantum dots and the third type of quantum dots. The second type of quantum dots with anionic groups and the third type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer, or the third type of quantum dots with anionic groups and the second type of quantum dots with cationic groups are assembled by fusion to form the light-emitting layer.

[0114] In one embodiment, in a quantum dot light-emitting device with a relatively balanced hole-electron, the composite material forming the light-emitting layer is a combination of a first type of quantum dot with a non-hole-confining core-shell structure and a second type of quantum dot with a non-electron-confining core-shell structure. Anionic groups are connected to the surface of one of the first type of quantum dot and the second type of quantum dot, and cationic groups are connected to the surface of the other of the first type of quantum dot and the second type of quantum dot. The first type of quantum dot with anionic groups and the second type of quantum dot with cationic groups are assembled by fusion to form the light-emitting layer, or the second type of quantum dot with anionic groups and the first type of quantum dot with cationic groups are assembled by fusion to form the light-emitting layer.

[0115] In another alternative embodiment, in a quantum dot light-emitting device with a relatively balanced hole-electron, the composite material forming the light-emitting layer is a third type of quantum dot with a type-I electron-confining and hole-confining core-shell structure. Anionic groups are connected to the surface of a part of the third type of quantum dot, and cationic groups are connected to the surface of another part of the third type of quantum dot. The third type of quantum dot with anionic groups and the third type of quantum dot with cationic groups are assembled by fusion to form the light-emitting layer.

[0116] In yet another alternative embodiment, in a quantum dot light-emitting device with a relatively balanced hole-electron, the composite material forming the light-emitting layer is a mixture of a first type of quantum dot with a non-hole-confining core-shell structure, a second type of quantum dot with a non-electron-confining core-shell structure, and a third type of quantum dot with a type-I electron-confining and hole-confining core-shell structure. Anionic groups or cationic groups are connected to the surfaces of the first type of quantum dot, the second type of quantum dot, and the third type of quantum dot. Anionic groups are connected to the surface of at least one of the first type of quantum dot, the second type of quantum dot, and the third type of quantum dot, and cationic groups are connected to the surface of at least one of the first type of quantum dot, the second type of quantum dot, and the third type of quantum dot. The quantum dots with anionic groups and the quantum dots with cationic groups are assembled by fusion to form the light-emitting layer.

[0117] In some embodiments, the average particle size of the first quantum dot is 5 nm to 25 nm; and / or, the average particle size of the second quantum dot is 5 nm to 25 nm; for example, the average particle size of the first quantum dot or the second quantum dot can be 7 nm, 9 nm, 11 nm, 13 nm, 15 nm, 17 nm, 19 nm, 21 nm, 23 nm, and values between any two of the above values or ranges between any two of the above values.

[0118] In some embodiments, the first quantum dot and the second quantum dot each independently include one or more of a single-structure quantum dot, a core-shell structure quantum dot, and a perovskite-type semiconductor material.

[0119] Among them, the material of the single-structure quantum dots, the core material of the core-shell structure quantum dots, and the shell material of the core-shell structure quantum dots may respectively include one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds.

[0120] The II-VI group compounds include one or more of 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.

[0121] The IV-VI group compounds include one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe; the III-V group compounds include one or more of 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; and the I-III-VI group compounds include one or more of CuInS2, CuInSe2, and AgInS2.

[0122] The perovskite semiconductor material includes doped or undoped inorganic perovskite semiconductors or organic-inorganic hybrid perovskite semiconductors. The structural general formula of the inorganic perovskite semiconductor is AMX3, where A is Cs + ions, M is a divalent metal cation, including Pb2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ one or more of, X is a halogen anion, including Cl - , Br - , I - one or more of, the structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or

[0123] [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ one or more of, X is a halogen anion, including Cl - , Br - , I - one or more of.

[0124] In a third aspect, an embodiment of the present application provides a preparation method for preparing the above composite material, and the preparation method includes:

[0125] In the first step, provide a third quantum dot solution including third quantum dots, where the third quantum dot solution includes a first organic solvent and third quantum dots dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dots;

[0126] Provide an anion ligand solution including an anion group, where the anion ligand solution includes a second organic solvent and an anion ligand dispersed in the second organic solvent;

[0127] The first ligand used in the first step includes a conventional organic ligand. A composite material connected with the conventional organic ligand is prepared by using related technologies. The synthesis method of the composite material connected with the conventional organic ligand includes processes such as the one-pot method or the two-step method in related technologies. According to specific requirements, the core of the quantum dots of a binary alloy or a multi-component alloy is synthesized, and at least one shell layer of the quantum dots is generated by the alternating ion layer adsorption method;

[0128] The anion ligand used in the first step includes Na2S or (NH4)2S. The first organic solvent is an alkane reagent. Suitable alkane reagents include one of n-hexane reagent and n-octane reagent. The second organic solvent includes NMF (N-methylformamide) solution, DMSO (dimethyl sulfoxide) solvent, MEK (methyl ethyl ketone) solvent, ACN (acetonitrile) solvent or a thiol organic solvent. Suitable thiol organic solvents include mercaptoethanol.

[0129] In the second step, anion ligand exchange is used to obtain the first quantum dots QDs / S with anionic groups 2- , and the specific steps include:

[0130] Mix the third quantum dot solution with the anion ligand solution. The anionic group exchanges ligands with the first ligand to obtain the first quantum dots, and the surface of the first quantum dots is connected with anionic groups;

[0131] After separating the first quantum dots, disperse them in the second organic solvent to obtain the first quantum dot solution;

[0132] The process diagram of the anion ligand exchange can be referred to in the appendix Figure 3 as shown. In order to promote the first quantum dots to enter the second organic solvent, the immiscible first organic solvent and the second solvent are stirred under the protection of an inert atmosphere. The stirring time is 1 min to 10 min. Through stirring, QDs / S 2- is completely transferred to the phase of the second organic solvent; the separation and purification method of the first quantum dots includes: washing the mixed solution containing the first quantum dots in the second step with n-hexane. The number of washing times can be two or more times, and precipitation is carried out with acetonitrile to obtain a precipitate, and the precipitate is the purified first quantum dots;

[0133] In the third step, cation ligand exchange is used to form the second quantum dots QDs / M with cationic groups 2+ , and the specific steps include:

[0134] Provide a cation ligand solution including cationic groups. The cation ligand solution includes a third organic solvent and a cation ligand dispersed in the third organic solvent;

[0135] Mix the first quantum dot solution with the cationic ligand solution. The cationic group and the anionic group undergo ligand exchange to obtain a second quantum dot, and the surface of the second quantum dot is connected with a cationic group;

[0136] Disperse the second quantum dot in a second organic solvent to obtain a second quantum dot solution;

[0137] The cationic ligand used in the third step includes a metal salt, and suitable metals include one of Cd, Zn, Pb, Hg, and In. The third organic solvent includes NMF (N-methylformamide) solvent, DMSO (dimethyl sulfoxide) solvent, MEK (methyl ethyl ketone) solvent, or ACN (acetonitrile) solvent.

[0138] For the process diagram of cation exchange, please refer to the appendix Figure 3 As shown, to promote the entry of the second quantum dot QDs / M 2+ into the second organic solvent, precipitate the second quantum dot with ethyl acetate, and disperse the precipitate in the second organic solvent;

[0139] Step 4: Fuse and assemble the first quantum dot and the second quantum dot to obtain a quantum dot fusion unit. The specific steps include:

[0140] Mix the first quantum dot solution with the second quantum dot solution, and fuse and assemble the first quantum dot and the second quantum dot into a quantum dot fusion unit;

[0141] Among them, the step of mixing the first quantum dot solution and the second quantum dot solution includes adding the first quantum dot solution to a flask and stirring for a period of time. The stirring method is ultrasonic for 10 s to 60 s. Under the condition of vigorous stirring, add the second quantum dot solution, and continue to stir the mixed solution for 1 h to 24 h. The first quantum dot QDs / S 2- and the second quantum dot QDs / M 2+ are fused and assembled to form a QDs-QDs quantum dot fusion unit. The fusion and assembly process can be referred to in the appendix Figure 4 As shown;

[0142] Step 5: Separate the quantum dot fusion unit and disperse it in a fourth organic solvent for later use. The separation operation of the quantum dot fusion unit includes: Prepare n-hexane reagent. Adding oleylamine and oleic acid to the n-hexane reagent will cause phase layer separation. Transfer the mixed solution containing QDs-QDs to the upper organic phase. After the phase transfer is complete, add ethanol to form a precipitate. This precipitate is purified QDs-QDs, and disperse the QDs-QDs in octane reagent for later use.

[0143] It should be noted that in the quantum dot fusion unit prepared by the above preparation method, the core-shell structure of the first quantum dot is basically the same as that of the second quantum dot.

[0144] It should be noted that in the preparation process of the above second quantum dot, the first quantum dot is obtained by first performing an anion ligand exchange on the third quantum dot, and then the second quantum dot is obtained by performing a cation ligand exchange on the first quantum dot. Since the surfaces of the quantum dots are all rich in cations but are connected with organic ligands, it is necessary to replace the organic ligands with anionic groups and then perform further operations. That is, it is generally difficult to directly connect cations to the surface of the quantum dots. Therefore, it is necessary to first connect an anionic ligand and then perform a cation exchange to obtain the second quantum dot.

[0145] Taking Na2S or (NH4)2S as an example of the anionic ligand, the concentration of the anionic ligand in the above anionic ligand solution is 1 mmol / ml to 10 mmol / ml. It can be understood that the concentration of the anionic ligand in the anionic ligand solution can be 2 mmol / ml, 3 mmol / ml, 4 mmol / ml, 5 mmol / ml, 6 mmol / ml, 7 mmol / ml, 8 mmol / ml, 9 mmol / ml, and the concentration or range between any two of the above concentrations.

[0146] Taking zinc acetate as an example of the cationic ligand, the concentration of the cationic ligand in the above cationic ligand solution is 0.1 mmol / ml to 10 mmol / ml. It can be understood that the concentration of the cationic ligand in the cationic ligand solution is 0.2 mmol / ml, 0.5 mmol / ml, 0.8 mmol / ml, 1 mmol / ml, 2 mmol / ml, 3 mmol / ml, 4 mmol / ml, 5 mmol / ml, and the concentration or range between any two of the above concentrations.

[0147] Fifthly, an embodiment of the present application further provides a preparation method for preparing a quantum dot fusion unit with different core-shell structures, wherein the core-shell structure of the first quantum dot is different from that of the second quantum dot. The preparation method includes:

[0148] The first step is to provide a third quantum dot solution including a third quantum dot, wherein the third quantum dot solution includes a first organic solvent and the third quantum dot dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dot;

[0149] Provide a fourth quantum dot solution including a fourth quantum dot, wherein the fourth quantum dot solution includes a first organic solvent and the fourth quantum dot dispersed in the first organic solvent, and a first ligand is connected to the surface of the fourth quantum dot;

[0150] Provide an anionic ligand solution including an anionic group, where the anionic ligand solution includes a second organic solvent and an anionic ligand dispersed in the second organic solvent;

[0151] In the second step, perform anionic ligand exchange to obtain the first quantum dots QDs / S with an anionic group 2- , specifically including:

[0152] Mix the third quantum dot solution with the anionic ligand solution, and perform ligand exchange between the anionic group and the first ligand to obtain the first quantum dots. The surface of the first quantum dots is connected with an anionic group, and disperse the first quantum dots in the second organic solvent to obtain a second quantum dot solution;

[0153] In the second step, it also includes performing anionic ligand exchange to obtain a third quantum dot group with an anionic group, specifically including:

[0154] Mix the fourth quantum dot solution with the anionic ligand solution, and perform ligand exchange between the anionic group and the first ligand to obtain the fifth quantum dots. The surface of the fifth quantum group is connected with an anionic group, and disperse the fifth quantum dots in the second organic solvent to obtain a fifth quantum dot solution;

[0155] In the third step, perform cationic ligand exchange to form the second quantum dots QDs / M with a cationic group 2+ , specifically including:

[0156] Provide a cationic ligand solution including a cationic group, where the cationic ligand solution includes a third organic solvent and a cationic ligand dispersed in the third organic solvent;

[0157] Mix the fifth quantum dot solution with the cationic ligand solution, and perform ligand exchange between the cationic group and the anionic group to obtain the second quantum dots. The surface of the second quantum dots is connected with a cationic group, and disperse the second quantum dots in the second organic solvent to obtain a second quantum dot solution;

[0158] In the fourth step, fuse and assemble the first quantum dots and the second quantum dots to obtain a quantum dot fusion unit. The specific steps include:

[0159] Mix the first quantum dot solution with the second quantum dot solution, and fuse and assemble the first quantum dots and the second quantum dots to obtain a quantum dot fusion unit;

[0160] In the fifth step, the quantum dot fusion unit is separated and then dispersed in a fourth organic solvent for later use. The separation operation of the quantum dot fusion unit includes: preparing a n - hexane reagent. Adding oleylamine and oleic acid to the n - hexane reagent will cause phase - layer separation. Transfer the mixed solution containing QDs - QDs to the upper organic phase. After the phase transfer is complete, add ethanol to form a precipitate, and this precipitate is the purified QDs - QDs. Then disperse the QDs - QDs in an octane reagent for later use.

[0161] The following specifically describes the present application through specific embodiments. The following embodiments are only partial embodiments of the present application and do not limit the present application. The raw materials used in the following embodiments are all commercially available products without special instructions.

[0162] Example 1

[0163] Example 1 provides a quantum dot light - emitting device, which includes an anode, a hole - injection layer, a hole - transport layer, a light - emitting layer, an electron - transport layer, and a cathode. The material of the anode is ITO, the material of the hole - injection layer is PEDOT:PSS (poly[3,4 - ethylenedioxythiophene]:polystyrene sulfonate), the material of the hole - transport layer is TFB (poly[(9,9 - dioctylfluorene - 2,7 - diyl)-co-(4,4′-(N-(4 - sec - butylphenyl)diphenylamine)]), the material of the electron - transport layer is ZnO, and the material of the cathode is Ag.

[0164] The material of the light - emitting layer of the quantum dot light - emitting device in Example 1 is a green composite material. The bandgap of this quantum dot is 2.28 eV. The preparation method of the composite material includes:

[0165] In the first step, provide a third quantum dot and a fourth quantum dot with different core - shell structures. The third quantum dot has a non - electron - confinement structure, and the materials on each layer of the third quantum dot are configured as InZnP / ZnSeS. The organic ligands connected to the surface of the third quantum dot are oleic acid and oleylamine. The fourth quantum dot includes a type - I electron - confinement and hole - confinement structure, and the materials on each layer of the fourth quantum dot are InP / ZnS. The organic ligands connected to the surface of the fourth quantum dot are oleic acid and oleylamine;

[0166] Among them, by adjusting the proportion of alloy components on each layer of the first quantum dot, the valence - band energy - level difference ΔE VB,壳-核 =-0.5 eV, and the conduction - band energy - level difference ΔE CB,壳-核 =0.15 eV. Electrons can be delocalized on the conduction band of the core - shell of this quantum dot. By adjusting the proportion of alloy components on each layer of the second quantum dot, the valence - band energy - level difference ΔE VB,壳-核 =-1.2 eV, and the conduction - band energy - level difference ΔE CB,壳-核 =1 eV; Specifically,

[0167] 200 mg of InP / ZnS was dispersed in 5 ml of n - hexane solvent to obtain the third quantum dot solution;

[0168] 200 mg of InZnP / ZnSeS was dispersed in 5 ml of n - hexane solvent to obtain the fourth quantum dot solution;

[0169] The second step is anion ligand exchange, specifically including:

[0170] A 5 - ml n - hexane solution containing 200 mg of InP / ZnS was mixed with a 10 - ml NMF solution containing 50 mmol of (NH4)2S. The immiscible two - phase solvents were stirred in an inert atmosphere for 8 minutes. It can be observed that the organic ligands on the surface of the third quantum dots are stripped and connected to S 2- and InP / ZnS / S is formed 2- wherein InP / ZnS / S 2- is transferred to the NMF phase. The NMF phase where InP / ZnS / S 2- is located was washed twice with n - hexane reagent, and then ethyl formate was added to obtain the precipitate of InP / ZnS / S 2- The precipitate of InP / ZnS / S 2- was separated and dispersed in 4 mL of NMF solvent;

[0171] A 5 - ml n - hexane solution containing 200 mg of InZnP / ZnSeS was mixed with a 10 - ml NMF (N - methylformamide) solution containing 50 mmol of (NH4)2S. The immiscible two - phase solvents were stirred in an inert atmosphere for 8 minutes. It can be observed that the organic ligands on the surface of the fourth quantum dots are stripped and connected to S 2- and InZnP / ZnSeS / S is formed 2- wherein InZnP / ZnSeS / S 2- is transferred to the NMF phase. The NMF phase where InZnP / ZnSeS / S 2- is located was washed twice with n - hexane reagent, and then ethyl formate was added to obtain the precipitate of InZnP / ZnSeS / S 2 The precipitate was separated and dispersed in 4 mL of NMF solvent;

[0172] The third step is to perform cation ligand exchange on InZnP / ZnSeS / S 2- to obtain InZnP / ZnSeS - / Zn 2+ specifically including:

[0173] Dissolve 100 mg of zinc acetate in 2 ml of NMF (N-methylformamide) solvent to form a cationic ligand solution, and add the cationic ligand solution to the NMF solution containing InZnP / ZnSeS / S 2- in Step 2, stir the solution for 2 h to obtain InZnP / ZnSeS / Zn 2+ Second quantum dots, add ethyl acetate to form a precipitate of InZnP / ZnSeS / Zn 2+ , disperse the precipitate in 5 ml of NMF solvent for later use;

[0174] Fourth step, add the NMF solution containing InZnP / ZnSeS / Zn 2+ to a flask, ultrasonicate for 30 seconds, and under the condition of vigorous stirring, add the NMF solution containing InP / ZnS / S 2- , stir the mixture for 10 h to obtain a fused quantum dot unit of InZnP / ZnSeS / Zn 2+ and InP / ZnS / S 2- ;

[0175] Fifth step, purify the fused quantum dot unit of InZnP / ZnSeS / Zn 2+ and InP / ZnS / S 2- and store it. Specifically, add 10 ml of a hexane mixed solution to the mixed solution, where the hexane mixed solution contains 2 ml of oleylamine and 2 ml of oleic acid, stir for 30 min, and transfer the fused quantum dot unit of InZnP / ZnSeS / Zn 2+ and InP / ZnS / S 2- to the organic phase of hexane. After complete phase transfer, add ethanol to the organic phase to form a precipitate, and the precipitate is the fused quantum dot unit of InZnP / ZnSeS / Zn 2+ and InP / ZnS / S 2- . Disperse the precipitate in octane reagent for later use.

[0176] The preparation method of the quantum dot light-emitting device of Example 1 includes: spin-coating a hole injection layer of PEDOT:PSS material on the anode layer ITO, and performing thermal annealing on a hot plate at 100 °C for 15 min; then forming a hole transport layer of 30 nm TFB on the hole injection layer, and performing thermal annealing on a hot plate at 100 °C for 15 min; forming a light-emitting layer of green quantum dots with a composition of InZnP / ZnSe / Zn 2+ and InP / ZnS / S 2- on the hole transport layer; coating an ethanol solution dispersed with ZnO on the light-emitting layer, and performing thermal annealing on a hot plate at 80 °C for 10 min to obtain an electron transport layer; finally, forming an Ag cathode electrode layer by evaporation and encapsulating to form an electroluminescent device.

[0177] The optoelectronic properties and lifetime of the quantum dot light-emitting device prepared in Example 1 were tested, and the test results are shown in Table 1 below.

[0178] Example 2

[0179] Example 2 provides a quantum dot light-emitting device. The materials of the anode, hole injection layer, hole transport layer, and cathode of this quantum dot light-emitting device are the same as those of the corresponding functional layers in Example 1. The difference is that the material of the electron transport layer in Example 2 is ZnMgO, and the light-emitting layer uses a red quantum dot fusion unit.

[0180] The material of the light-emitting layer of the quantum dot light-emitting device in Example 2 is a red composite material. The bandgap of this quantum dot is 1.97 eV. The preparation method of the composite material includes:

[0181] In the first step, a third quantum dot is provided. The third quantum dot has a non-hole confinement structure. The materials on each layer of the quantum dot are configured as CdZnSeS / ZnSe / ZnSeS, and the organic ligand connected to the surface of the quantum dot is oleic acid;

[0182] Among them, by adjusting the proportion of alloy components on each layer of the quantum dot, the valence band energy level difference ΔE VB,壳-核 =-0.1 eV, and the conduction band energy level difference ΔE CB,壳-核 =0.55 eV. Holes can be delocalized on the conduction band of the core-shell of this quantum dot.

[0183] In the second step, CdZnSeS / ZnSe / ZnSeS / S 2- is obtained through anionic ligand exchange. The operation of the specific anionic ligand exchange process is the same as that in Example 1;

[0184] In the third step, CdZnSeS / ZnSe / ZnSeS / S 2- is obtained as CdZnSeS / ZnSe / ZnSeS / Zn 2+ through cationic ligand exchange. The operation of the specific cationic ligand exchange process is the same as that in Example 1;

[0185] In the fourth step, CdZnSeS / ZnSe / ZnSeS / Zn 2+ and CdZnSeS / ZnSe / ZnSeS / S 2- are fused and assembled to obtain a fused quantum dot unit of CdZnSeS / ZnSe / ZnSeS / Zn 2+ and CdZnSeS / ZnSe / ZnSeS / S 2- ; the operation of the specific fusion and assembly is the same as that in Example 1;

[0186] Step 5: Purify CdZnSeS / ZnSe / ZnSeS / Zn 2+ Fuse with the CdZnSeS / ZnSe / ZnSeS / S 2- quantum dot unit and save it. The specific purification method and storage method are the same as those in Example 1.

[0187] The preparation method of the quantum dot light-emitting device in Example 2 is the same as that in Example 1, except that the light-emitting layer uses the above-mentioned red quantum dot fusion unit, and the electron transport layer uses ZnMgO.

[0188] The optoelectronic properties and lifespan of the quantum dot light-emitting device prepared in Example 2 were tested, and the test results are shown in Table 1 below.

[0189] Comparative Example 1

[0190] The quantum dot light-emitting device provided in Comparative Example 1 is basically the same as that in Example 1, except that the light-emitting layers are green quantum dots of InZnP / ZnSeS with a non-electron confinement structure and InP / ZnS with a type-I electron confinement and hole confinement structure, respectively.

[0191] The optoelectronic properties and lifespan of this quantum dot light-emitting device were tested, and the test results are shown in Table 1 below.

[0192] Comparative Example 2

[0193] The quantum dot light-emitting device in Comparative Example 2 is basically the same as that in Example 2, except that the light-emitting layer is a CdZnSeS / ZnSe / ZnSeS red quantum dot with a non-hole confinement structure.

[0194] The optoelectronic properties and lifespan of this quantum dot light-emitting device were tested, and the test results are shown in Table 1 below.

[0195] Description of the test equipment for the optoelectronic properties and lifespan of the quantum dot light-emitting device: The lifespan of the quantum dot light-emitting device was tested using a 128-channel lifespan test system customized by Guangzhou New Vision Company. The system architecture is a constant voltage and constant current source driving QLED to test the change of the test voltage or current; a photodiode detector and a test system are used to test the change of the brightness (photoelectric current) of the QLED; a luminance meter is used to calibrate the brightness (photoelectric current) of the QLED.

[0196] The PL parameters obtained by optically exciting the quantum dot light-emitting device to emit light are used to describe the wavelength (nm) corresponding to the maximum intensity of the quantum dot light emission, the FWHM parameter is used to describe the width of the peak-valley of the emission peak (nm), and the PLQY parameter is used to evaluate the quantum dot light-emitting efficiency.

[0197] The EL parameters for the light emission of the quantum dot light-emitting device excited by an electric field are used to describe the wavelength (nm) corresponding to the maximum intensity of electroluminescence. The FWHM parameter is used to describe the width (nm) of the peak valley of the emission peak. The EQE parameter is used to evaluate the efficiency of electrons injected into the composite material and converted into photons in the light-emitting device. T 95 T in the @1000nit parameter 95 represents the time taken for the light emission intensity of the light-emitting device to decrease to 95% of the maximum value. The unit can be hours or minutes. 1000nit represents that the light emission intensity of the light-emitting device is 1000 nits. This parameter is generally used to test and evaluate the stability and durability of the light-emitting device, especially the long-term use performance under high brightness conditions.

[0198] The above parameters are tested as shown in Table 1 and Table 2 below:

[0199]

[0200] Table 1 Test results of the light emission performance and life performance of the light-emitting device

[0201]

[0202] Table 2 Test results of the light emission performance and life performance of the quantum dot light-emitting device

[0203] From the test data in Table 1, it can be seen that the PLQY parameter of Example 1 has a significant improvement compared to that of Comparative Example 1. Correspondingly, the fluorescence quantum yield and stability of the quantum dot light-emitting device provided by Example 1 are significantly improved. The PLQY parameter of Example 2 has a significant improvement compared to that of Comparative Example 2. Correspondingly, the fluorescence quantum yield and stability of the quantum dot light-emitting device provided by Example 2 are significantly improved. That is, through the process of fusing and assembling the first quantum dot with a negative charge and the second quantum dot, the defect state on the surface of the quantum dot can be repaired, which is conducive to improving the fluorescence quantum yield and stability.

[0204] From the test data in Table 2, it can be seen that the EQE parameter of Example 1 has a significant improvement compared to that of Comparative Example 1. Correspondingly, the photon conversion rate of the quantum dot light-emitting device provided by Example 1 is significantly improved. The EQE parameter of Example 2 has a significant improvement compared to that of Comparative Example 2. Correspondingly, the photon conversion rate of the quantum dot light-emitting device provided by Example 2 is significantly improved;

[0205] From the test data in Table 2, it can be seen that the T95@1000nit parameter of Example 1 has a significant improvement compared to that of Comparative Example 1. Correspondingly, the life performance of the quantum dot light-emitting device provided by Example 1 is significantly improved. The T95@1000nit parameter of Example 2 has a significant improvement compared to that of Comparative Example 2. Correspondingly, the life performance of the quantum dot light-emitting device provided by Example 2 is significantly improved;

[0206] Regarding the test data in Table 2, it should be noted that for the green quantum dot light-emitting devices in the cadmium-free system provided in Example 1 and Comparative Example 1, due to the energy level characteristics of their materials, the lifetime performance is poor, which is a normal phenomenon. For the quantum dot light-emitting devices in the cadmium-containing system provided in Example 2 and Comparative Example 2, due to the relatively mature preparation process level, their lifetime level is relatively high, which is a normal phenomenon.

[0207] The above has introduced in detail the quantum dots, quantum dot inks and light-emitting devices provided in the embodiments of the present application. Specific examples are used herein to elaborate on the principle and implementation manner of the present application. The description of the above embodiments is only used to help understand the method and its core idea of the present application; at the same time, for those skilled in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A composite material, characterized in that, The composite material includes a first quantum dot and a second quantum dot. Among them, anionic groups are connected to the surface of the first quantum dot, and cationic groups are connected to the surface of the second quantum dot.

2. The composite material according to claim 1, characterized in that, The element forming the anionic group includes one of S, Se, Te, and P; and / or, the element forming the cationic group includes one of Cd, Zn, Pb, Hg, and In; Optionally, the material of the second quantum dot includes at least one metal element, and the element forming the cationic group is selected from the metal elements in the material of the second quantum dot; and / or, the number of charges of the anionic group is the same as that of the cationic group, or the ratio of the amount of charge of the anionic group to the amount of charge of the cationic group is 0.8 - 1.2:

1.

3. The composite material according to claim 1, characterized in that, Both the first quantum dot and the second quantum dot are core-shell quantum dots. In the first quantum dot, the anionic group is connected to the outer layer of its shell; and / or, in the second quantum dot, the cationic group is connected to the outer layer of its shell.

4. The composite material according to claim 1, characterized in that, The composite material includes a first type of quantum dot with a first core-shell structure, a second type of quantum dot with a second core-shell structure, and a third type of quantum dot with a third core-shell structure. The first core-shell structure is configured as a non-hole confinement structure, the second core-shell structure is configured as a non-electron confinement structure, and the third core-shell structure is configured as a type-I electron and hole confinement structure; Among them, both the first quantum dot and the second quantum dot are configured as the first type of quantum dot with a first core-shell structure, such that the composite material is configured to be conducive to hole injection; Or, one of the first quantum and the second quantum dot is configured as the first type of quantum dot with a first core-shell structure, and the other of the first quantum and the second quantum dot is configured as the third type of quantum dot with a third core-shell structure, such that the composite material is configured to be conducive to hole injection; Or, both the first quantum dot and the second quantum dot are configured as the second type of quantum dot with a second core-shell structure, such that the composite material is configured to be conducive to electron injection; Or, one of the first quantum and the second quantum dot is configured as the second type of quantum dot with a second core-shell structure, and the other of the first quantum and the second quantum dot is configured as the third type of quantum dot with a third core-shell structure, such that the nanomaterial is configured to be conducive to electron injection; Or, both the first quantum dot and the second quantum dot are configured as the third type of quantum dot with a third core-shell structure, such that the quantum dot is configured to be conducive to the balanced transport of holes and electrons; Or, one of the first quantum dot and the second quantum dot includes the first type of quantum dot with a first core-shell structure, and the other of the first quantum and the second quantum dot is configured as the second type of quantum dot with a second core-shell structure, such that the quantum dot is configured to be conducive to the balanced transport of holes and electrons; Alternatively, the first quantum dots include a first type of quantum dots having a first core-shell structure, a second type of quantum dots having a second core-shell structure, and a third type of quantum dots having a third core-shell structure, and the second quantum dots include a first type of quantum dots having a first core-shell structure, a second type of quantum dots having a second core-shell structure, and a third type of quantum dots having a third core-shell structure, such that the quantum dots are configured to facilitate balanced hole and electron transport.

5. The composite material according to any one of claims 1-4, characterized in that, The average particle size of the first quantum dots is 5 nm to 25 nm; and / or, the average particle size of the second quantum dots is 5 nm to 25 nm; And / or, the first quantum dot and the second quantum dot each independently include one or more of a single-structure quantum dot, a core-shell structure quantum dot, and a perovskite semiconductor material. Among them, the material of the single-structure quantum dot, the core material of the core-shell structure quantum dot, and the shell material of the core-shell structure quantum dot may each independently include one or more of II-VI group compounds, IV-VI group compounds, III-V group compounds, and I-III-VI group compounds. The II-VI group compounds include one or more of 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. The IV-VI group compounds include one or more of SnS, SnSe, SnTe, PbS, PbSe, PbTe, SnSeS, SnSeTe, SnSTe, PbSeS, PbSeTe, PbSTe, SnPbS, SnPbSe, SnPbTe, SnPbSSe, SnPbSeTe, and SnPbSTe. The III-V group compounds include one or more of 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. The I-III-VI group compounds include one or more of CuInS2, CuInSe2, and AgInS2. The perovskite semiconductor material includes doped or undoped inorganic perovskite semiconductors or organic-inorganic hybrid perovskite semiconductors. The structural general formula of the inorganic perovskite semiconductor is AMX3, where A is a Cs + ion, M is a divalent metal cation, including Pb 2+ and Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2 + , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following. The structural general formula of the organic-inorganic hybrid perovskite semiconductor is BMX3, where B is an organic amine cation, including CH3(CH2) n-2 NH3 + or [NH3(CH2) n NH3] 2+ , where n≥2, M is a divalent metal cation, including Pb 2+ , Sn 2+ , Cu 2+ , Ni 2+ , Cd 2+ , Cr 2+ , Mn 2+ , Co 2+ , Fe 2+ , Ge 2+ , Yb 2+ , Eu 2+ One or more of the following, X is a halogen anion, including Cl - , Br - , I - One or more of the following.

6. A method for preparing a composite material, characterized in that, comprising the following steps: Providing a third quantum dot solution including third quantum dots, wherein the third quantum dot solution includes a first organic solvent and the first quantum dots dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dots; Providing an anionic ligand solution including anionic groups, wherein the anionic ligand solution includes a second organic solvent and the anionic ligands dispersed in the second organic solvent; Mixing the third quantum dot solution with the anionic ligand solution, and performing ligand exchange between the anionic groups and the first ligand to obtain first quantum dots, and anionic groups are connected to the surface of the first quantum dots; Dispersing the first quantum dots in a second organic solvent to obtain a first quantum dot solution; Providing a cationic ligand solution including cationic groups, wherein the cationic ligand solution includes a third organic solvent and the cationic ligands dispersed in the third organic solvent; Mixing the first quantum dot solution with the cationic ligand solution, and performing ligand exchange between the cationic groups and the anionic groups to obtain second quantum dots, and cationic groups are connected to the surface of the second quantum dots; Dispersing the second quantum dots in a second organic solvent to obtain a second quantum dot solution; Mixing the first quantum dot solution with the second quantum dot solution to obtain the composite material.

7. A method for preparing a composite material, characterized in that, comprising the following steps: Providing a third quantum dot solution including third quantum dots, wherein the third quantum dot solution includes a first organic solvent and the third quantum dots dispersed in the first organic solvent, and a first ligand is connected to the surface of the third quantum dots; Providing a fourth quantum dot solution including fourth quantum dots, wherein the fourth quantum dot solution includes a first organic solvent and the fourth quantum dots dispersed in the first organic solvent, and a second ligand is connected to the surface of the fourth quantum dots; Providing an anionic ligand solution including anionic groups, the anionic ligand solution includes a second organic solvent and the anionic ligands dispersed in the second organic solvent; Mixing the third quantum dot solution with the anionic ligand solution, and performing ligand exchange between the anionic groups and the first ligand to obtain first quantum dots, and anionic groups are connected to the surface of the first quantum dots, and dispersing the first quantum dots in the second organic solvent to obtain a first quantum dot solution; Mix the fourth quantum dot solution with the anion ligand solution. The anion group undergoes ligand exchange with the second ligand to obtain a fifth quantum dot. The surface of the fifth quantum dot is connected with an anion group, and the fifth quantum dot is dispersed in the second organic solvent to obtain a fifth quantum dot solution; Provide a cation ligand solution including a cation group. The cation ligand solution includes a third organic solvent and a cation ligand dispersed in the third organic solvent; Mix the fifth quantum dot solution with the cation ligand solution. The cation group undergoes ligand exchange with the anion group to obtain a second quantum dot. The surface of the second quantum dot is connected with a cation group, and the second quantum dot is dispersed in the second organic solvent to obtain a second quantum dot solution; Mix the first quantum dot solution with the second quantum dot solution to obtain the composite material.

8. The method for preparing the composite material according to claim 6 or 7, characterized in that, The anion ligand includes Na2S or (NH4)2S; And / or, the cation ligand includes a soluble metal salt, and the metal element in the soluble metal salt includes one of Cd, Zn, Pb, Hg, and In.

9. The preparation method of the composite material according to claim 8, characterized in that, The first organic solvent includes alkanes with 6 - 18 carbon atoms; And / or, the second organic solvent includes NMF, DMSO, MEK, ACN, or a thiol organic solvent; And / or, the third organic solvent includes NMF, DMSO, MEK, or ACN; And / or, the first ligand includes capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, stearic acid, octanethiol, dodecyl mercaptan, octadecyl mercaptan, oleylamine, octadecylamine, octylamine, dioctylamine, trioctylamine, tri-n-octylphosphine, or tri-n-octyloxide; And / or, the second ligand includes capric acid, undecylenic acid, myristic acid, oleic acid, linoleic acid, stearic acid, octanethiol, dodecyl mercaptan, octadecyl mercaptan, oleylamine, octadecylamine, octylamine, dioctylamine, trioctylamine, tri-n-octylphosphine, or tri-n-octyloxide.

10. A quantum dot light-emitting device, characterized in that, It includes an anode, a cathode, and a light-emitting layer located between the anode and the cathode. The material forming the light-emitting layer includes the composite material according to any one of claims 1 - 5, or the material forming the light-emitting layer is prepared by the preparation method according to any one of claims 6 - 9.

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