CN114316942A - Composite material, preparation method thereof and light-emitting diode - Google Patents
Composite material, preparation method thereof and light-emitting diode Download PDFInfo
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Abstract
The application relates to the technical field of display, and provides a composite material, a preparation method thereof and a light-emitting diode. The composite material provided by the application comprises luminescent quantum dots, non-luminescent quantum dots and a connecting ligand, wherein the connecting ligand is connected with the luminescent quantum dots and the non-luminescent quantum dots. Therefore, the non-luminescent quantum dots are used as the protective quantum dots and are combined with the connecting ligand to modify the surface of the luminescent quantum dots, so that the surface defects of the luminescent quantum dots are effectively filled on the basis of not influencing the optical performance of the luminescent quantum dots, and the optical stability of the quantum dot material is improved; meanwhile, the non-luminescent quantum dots are connected with the luminescent quantum dots through the connecting ligands, so that the distance between the luminescent quantum dots is effectively increased, the agglomeration is avoided, the energy utilization efficiency is improved, and the composite material with ultrahigh monochromaticity and excellent luminescent performance is favorably obtained.
Description
Technical Field
The application belongs to the technical field of display, and particularly relates to a composite material, a preparation method thereof and a light-emitting diode.
Background
Quantum dots (quantum dots), a typical class of nanomaterials, with radii generally smaller or close to the exciton bohr radius, exhibit significant quantum dot confinement effects with unique optical properties, such as: the luminescent spectrum is continuously adjustable along with the size and components of the material, the half-peak width is narrow, the fluorescence efficiency is high, the service life is long, the monodispersity is excellent, the photo-thermal stability is strong, and the like. These unique properties make them widely used in the fields of displays, lighting, biomarkers and solar cells.
Compared with the conventional spherical or spheroidal zero-dimensional quantum dot, the two-dimensional nano-quantum dot has the basic characteristics of common quantum dots and also has the characteristics different from the zero-dimensional quantum dot, for example, the peak width of the zero-dimensional quantum dot is usually more than 20nm and cannot meet the standard that the peak width is less than 15nm, and the peak width of the two-dimensional nano-quantum dot is usually less than 15nm, so that the monochromaticity of the device can be remarkably improved, and the two-dimensional nano-quantum dot has an important significance in realizing a quantum dot light emitting diode (QLED) with high color purity.
The shell growth of the two-dimensional nano core-shell structure quantum dot synthesized by the prior art usually occurs on the surface of the whole core (the plane direction of the core is vertical to the plane direction) in the process of shell growth. Because the confinement effect of the two-dimensional nano core-shell structure quantum dot only occurs in the thickness direction, the wavelength red shift is easily caused when the conventional shell layer grows. However, if the shell growth only occurs in the direction perpendicular to the planar direction of the core, a large number of surface defects are often present on the surface in the planar direction, which affects the light emitting performance of the light emitting secondary light using the two-dimensional nano quantum dots as the light emitting layer material.
Disclosure of Invention
The application aims to provide a composite material, a preparation method thereof and a light-emitting diode, and aims to solve the problem that the light-emitting performance of the light-emitting diode is affected due to the fact that a large number of surface defects exist on the surface of the conventional quantum dot.
In order to achieve the purpose of the application, the technical scheme adopted by the application is as follows:
in a first aspect, the present application provides a composite material comprising luminescent quantum dots, non-luminescent quantum dots, and linking ligands linking the luminescent quantum dots and the non-luminescent quantum dots.
According to the composite material provided by the application, the non-luminescent quantum dots are modified on the surfaces of the connecting ligands, so that the surface defects of the luminescent quantum dots are effectively filled on the basis of not influencing the optical performance of the luminescent quantum dots, the function of the non-luminescent quantum dots as the protective quantum dots is exerted, the light-protective quantum dots are protected, the influence of external environmental factors such as water and oxygen invasion on the optical performance of the luminescent quantum dots is avoided, and the optical stability of the quantum dot material is improved; on the other hand, the non-luminescent quantum dots are connected with the luminescent quantum dots through the connecting ligands, so that the distance between the luminescent quantum dots can be effectively increased, the agglomeration is avoided, the resonance energy transfer caused by the undersized spacing of the luminescent quantum dots is reduced, the energy utilization efficiency is effectively improved, the luminous efficiency of the material is favorably improved, and the composite material with ultrahigh monochromaticity and excellent luminous performance is obtained.
In a second aspect, the present application provides a method of preparing a composite material, comprising the steps of:
providing luminescent quantum dots, non-luminescent quantum dots, a linking ligand and an acid;
and mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid and the connecting ligand in a solvent to obtain the composite material.
According to the preparation method of the composite material, the luminescent quantum dots, the non-luminescent quantum dots and the connecting ligands are used as raw materials, the acid is added, and in the step of mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid and the connecting ligands in the solvent, the acid is used for eliminating the surface defect states of the luminescent quantum dots and the non-luminescent quantum dots so as to promote the connecting ligands to respectively connect the luminescent quantum dots and the luminescent quantum dots, so that the luminescent quantum dots and the non-luminescent quantum dots are effectively connected, and the composite material with ultrahigh monochromaticity and excellent luminescent performance is obtained. The method is simple, simple and convenient to operate and suitable for large-scale mass production.
Preferably, the step of mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid and the linking ligand in a solvent comprises:
adding the luminescent quantum dots, the acid and the connecting ligand into a solvent, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours to obtain a first solution;
adding the non-luminescent quantum dots into the first solution, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours.
Preferably, the luminescent quantum dots are two-dimensional nano quantum dots;
further preferably, the non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nano-quantum dots.
Further preferably, the molar ratio of the acid to the sum of the luminescent quantum dots and the non-luminescent quantum dots is (0.1-2): 10;
further preferably, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid.
Preferably, the luminescent quantum dot has a core-shell structure, and a shell layer of the luminescent quantum dot grows only along the plane direction of the luminescent quantum dot;
further preferably, the non-light emitting quantum dots connect two planes in the thickness direction of the light emitting quantum dots.
Preferably, the non-luminescent quantum dot is a non-core-shell structure quantum dot, and the metal element of the non-luminescent quantum dot is in the same family as the metal element of the shell layer of the luminescent quantum dot, and/or the non-metal element of the non-luminescent quantum dot is in the same family as the non-metal element of the shell layer of the luminescent quantum dot;
further preferably, the shell material of the luminescent quantum dot is a II-VI semiconductor material, and the core material of the luminescent quantum dot is a II-VI semiconductor material or a III-V semiconductor material;
further preferably, the material of the non-luminescent quantum dots is a II-VI semiconductor material.
Preferably, the linking ligand comprises a first linking group for linking the luminescent quantum dots and a second linking group for linking the non-luminescent quantum dots, the first linking group and the second linking group are each independently selected from any one of a thiol group, a carboxyl group, a hydroxyl group, a sulfonic group, an amino group and a phosphoric group;
further preferably, the linking ligand is selected to be a mercaptoalkanoic acid.
Preferably, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1 (10-100); and/or
The molar ratio of the luminescent quantum dots to the connecting ligand is 1 (1-100).
In a third aspect, the present application provides a light emitting diode, including a light emitting layer, a material of the light emitting layer including: the composite material or the composite material prepared by the preparation method.
According to the light-emitting diode provided by the application, the material of the light-emitting layer comprises the composite material with ultrahigh monochromaticity and excellent light-emitting performance, so that the light-emitting stability of the light-emitting diode is improved, the light color purity is high, and the light-emitting performance is excellent.
Drawings
FIG. 1 is a flow chart of a method of making a composite material provided by an embodiment of the present application;
FIG. 2 is a flow chart of a method of making a composite material provided in another embodiment of the present application;
fig. 3 is a schematic structural diagram of a light emitting diode according to an embodiment of the present application;
fig. 4 is a schematic structural diagram of a light emitting diode according to another embodiment of the present application;
wherein, in the figures, the respective reference numerals: 1-anode, 21-hole injection layer, 22-hole transport layer, 3-luminescent layer, 4-electron transport layer, and 5-cathode.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present application more clearly apparent, the present application is further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.
In this specification, the term "and/or" describing an association relationship of associated objects means that there may be three relationships, for example, a and/or B, may mean: a is present alone, A and B are present simultaneously, and B is present alone. Wherein A and B can be singular or plural. The character "/" generally indicates that the former and latter associated objects are in an "or" relationship.
In the present specification, unless otherwise specified, the term "two-dimensional nano-quantum dot" refers to a plate-like (planar-like) nano-quantum dot, i.e., a nano-quantum dot whose length and width are greater than its thickness so as to be approximately viewed as two-dimensional. The term "planar direction of the two-dimensional nano quantum dot" refers to an extending direction of a plane of the two-dimensional nano quantum dot, i.e., a length × width direction, which is different from a thickness direction of the two-dimensional nano quantum dot. The phrase "the shell layer of the luminescent quantum dot grows only along the plane direction thereof" means that the shell layer grows only from the edge of the two-dimensional nano quantum dot along the plane direction thereof, and does not grow on the plane in the thickness direction of the two-dimensional quantum dot.
The embodiment of the application provides a composite material, which comprises luminescent quantum dots, non-luminescent quantum dots and a connecting ligand, wherein the connecting ligand is connected with the luminescent quantum dots and the non-luminescent quantum dots.
In the embodiments of the present application, a luminescent quantum dot refers to a type of luminescent material that intrinsically emits light under the action of light. Compared with the light-emitting quantum dots, the non-light-emitting quantum dots emit light in an extrinsic manner under the photoelectric action, such as surface state defects, or do not emit light under the photoelectric action at all.
The non-luminescent quantum dots are connected with the luminescent quantum dots through the connecting ligand, so that adverse effects caused by the fact that the connecting ligand is simultaneously connected with the two luminescent quantum dots are avoided, for example, fluorescence quenching is caused or the requirement of ultrahigh monochromaticity cannot be met due to too wide emission peak is caused, and good luminescent performance of the quantum dots is guaranteed.
In some embodiments, the luminescent quantum dots are two-dimensional nano-quantum dots. Compared with the traditional spherical or sphere-like zero-dimensional quantum dots, the two-dimensional nano quantum dots meet the standard that the peak width of the super-monochromaticity requirement is less than 15nm, and the luminescent quantum dots are set to be the two-dimensional nano quantum dots, so that the super-monochromaticity of the composite material is endowed.
On the basis of the above embodiment, the luminescent quantum dot has a core-shell structure, and a shell layer of the luminescent quantum dot grows only along a plane direction thereof. Therefore, the problem that the two-dimensional nano quantum dots with non-core-shell structures are easily attacked by external water and oxygen to reduce the luminous efficiency is solved; meanwhile, the shell layer of the luminescent quantum dot only grows along the plane direction of the two-dimensional nano quantum dot, so that the problem of red shift of the emitted light wavelength caused by the growth of the shell layer along the thickness direction of the two-dimensional nano quantum dot is avoided, and the ultrahigh monochromaticity of the luminescent quantum dot is ensured; moreover, the non-luminous quantum dots are mainly coated and modified on two side surfaces which are positioned in the thickness direction of the luminous quantum dots and are not grown with shell materials by selecting the quantum dots, so that the optical performance of the luminous quantum dots is not influenced while the thickness of the luminous quantum dots is increased. In a further embodiment, the non-light-emitting quantum dots are connected to two planes in the thickness direction of the light-emitting quantum dots, so that the non-light-emitting quantum dots cover and modify two side surfaces in the thickness direction of the light-emitting quantum dots, which is equivalent to forming protective shells on the two side surfaces to fill up surface defects on the two side surfaces in the thickness direction of the light-emitting quantum dots, thereby playing a role in protecting the light-emitting quantum dots.
Based on the above embodiment, the non-luminescent quantum dot is a quantum dot with a non-core-shell structure, the metal element of the non-luminescent quantum dot is in the same group as the metal element of the shell layer of the luminescent quantum dot, and/or the non-metal element of the non-luminescent quantum dot is in the same group as the non-metal element of the shell layer of the luminescent quantum dot. Compared with the quantum dots with the core-shell structure, the quantum dots with the non-core-shell structure have more surface defects, mainly generate surface defect state luminescence under the photoelectric action and cover intrinsic luminescence, and the non-luminescence quantum dots are selected as the quantum dots with the non-core-shell structure, so that the protection effect of the non-luminescence quantum dots can be fully exerted under the condition that the luminescence performance of the luminescence quantum dots is not influenced; on the other hand, the metal element of the non-luminescent quantum dot and the metal element of the shell of the luminescent quantum dot are in the same group, and/or the non-metal element of the non-luminescent quantum dot and the non-metal element of the shell of the luminescent quantum dot are in the same group, so that the consistency and continuity of the energy level structure of the luminescent quantum dot and the non-luminescent quantum dot are ensured, especially when the non-luminescent quantum dot is used as a protective shell in the thickness direction of the luminescent quantum dot, the energy level of the luminescent quantum dot in the thickness direction can be ensured to be continuous, the effective constraint effect of excitons is improved, and the luminescent performance of the composite material is improved to a certain extent.
Based on the above embodiment, the shell material of the luminescent quantum dot is II-VI semiconductor material, and the core material of the luminescent quantum dot is II-VI semiconductor material or III-V semiconductor material. Wherein the group II-VI semiconductor material includes, but is not limited to CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, ZnO, HgS, HgSe, HgTe, CdSeS, CdSeTe, CdSSTe, ZnSeS, ZnSeTe, ZnSTe, HgSeS, HgSeTe, HgSTe, CdZnS, CdZnSe, CdZnTe, CdHgS, CdHgSe, CdHgTe, HgZnS, HgZnSe, HgZnTe, CgZnTe, CdZnSeS, CdZnSeTe, CdHgSeTe, CdHgZnSeS, HgZnSeTe, and the like, and the group III-V semiconductor material includes, but is not limited to GaN, InGaP, GaInAs, GaSb, AlN, AlP, AlAs, AlSb, InP, InGaSb, GaInGanSb, GanGanNAb, InNSNAP, AlNSNAP, AlGanAs, AlGanGanAs, AlPSnAs, AlNSNAP, AlPSnAs, AlPSNAP, AlGanNAP, AlNSNAP, AlGanGanGanGanNAP, AlGanGanGanNAP, AlPSnNAP, AlPSnGanGanGanGanGanNAP, AlPSnNAP, AlPSnGanGanNAP, AlPSnNAP, AlGanNAP, AlnGanNAP, AlnGanGanGanGanGanNAb, AlnGanGanGanGanNAP, AlnGanGanGanGanGanGanGanGanGanGanNAP, AlPSnGanNAP, AlPSnNAb, AlPSnGanNAb, AlPSnGanNAP, AlPSnGanGanGanNAb, AlPSnGanGanGanGanGanGanGanGanGanGanGanGanGanNAP, AlPSnGanGanGanGanGanGanGanGanNAb, AlPSnGanGanNAb, AlPSnGanGanGanNAb, AlPSnGanGanGanGanGanGanGanNAP, AlPSnNAb, AlPSnGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanGanNab, AlPSnGanGanGanGanNab, AlPSnNab, AlnNab, AlPSnNap, AlPSnNab, AlnNab, AlnNap, AlnNab, AlnNap.
The non-light-emitting quantum dot may be a zero-dimensional quantum dot or a two-dimensional nano-quantum dot, and in some embodiments, the non-light-emitting quantum dot is a quantum dot formed by introducing water and oxygen in a reaction process, so that a large number of defect states are generated on the surface of the finally formed quantum dot, and when the quantum dot is subjected to light or electric excitation, the generated excitons are easily captured by the defect states, so that the quantum dot does not emit light or emits light in the defect states. Preferably, the non-luminescent quantum dots are made of II-VI semiconductor materials, and the non-luminescent quantum dots are made of materials identical to the shell materials of the luminescent quantum dots, so that the consistency and continuity of the two quantum dots on the energy level structure are ensured, and the effective confinement effect of excitons is improved.
On the basis of the above embodiment, the length of the luminescent quantum dot is 10-100nm, the width is 2-10 nm, and the thickness is 1-5 nm; the particle size of the non-luminous quantum dots is 3-15 nm. In this way, the light-emitting quantum dots are two-dimensional nano quantum dots, the non-light-emitting quantum dots are zero-dimensional quantum dots, and the non-light-emitting quantum dots are arranged more densely in the thickness direction of the light-emitting quantum dots by adjusting the sizes of the light-emitting quantum dots and the non-light-emitting quantum dots within the above range.
On the basis of the above embodiment, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1 (10-100). When the mass ratio of the non-luminescent quantum dots to the luminescent quantum dots is less than 10:1, the non-luminescent quantum dots serving as the protective quantum dots cannot completely cover the surface defects of the luminescent quantum dots, so that the luminescent performance of the device is reduced; when the mass ratio of the non-light-emitting quantum dots to the light-emitting quantum dots is greater than 100:1, the non-light-emitting quantum dots as the protective quantum dots are excessive, and the light-emitting performance of the device is easily lowered because the non-light-emitting quantum dots cannot emit light or emit light in a defective state. In specific embodiments, the mass ratio of luminescent quantum dots to non-luminescent quantum dots may be 1:10, 1:20, 1:30, 1:35, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1: 100.
The connecting ligand as a ligand for connecting the luminescent quantum dots and the non-luminescent quantum dots should comprise a connecting group capable of combining with the luminescent quantum dots and the non-luminescent quantum dots, and can be a bidentate ligand or a monodentate ligand. In some embodiments, the linking ligand comprises a first linking group for linking the luminescent quantum dots and a second linking group for linking the non-luminescent quantum dots; the first linking group and the second linking group are each independently selected from any one of a mercapto group, a carboxyl group, a hydroxyl group, a sulfonic acid group, an amino group, and a phosphoric acid group. The groups can be coordinated and combined with metal atoms on the surfaces of the quantum dots, so that the luminescent quantum dots and the non-luminescent quantum dots are connected. In further embodiments, the linking ligand is selected from a mercaptoalkanoic acid, wherein the mercaptoalkanoic acid includes, but is not limited to, 5-mercaptopentanoic acid, 8-mercaptooctanoic acid, 7-mercaptoheptanoic acid, 11-mercaptoundecanoic acid, and the like. The mercaptoalkanoic acid comprises two groups, namely a mercapto group and a carboxyl group, and the two groups have good coordination activity with metal atoms on the surfaces of quantum dots, and can firmly connect luminescent quantum dots and non-luminescent quantum dots; moreover, the mercaptoalkanoic acid is a linear structure compound, so that the luminescent quantum dots and the non-luminescent quantum dots are firmly connected together, and the phenomenon that the distance between the luminescent quantum dots and the non-luminescent quantum dots is too small is avoided.
In some embodiments, the molar ratio of the luminescent quantum dots to the linking ligands is 1 (1-100), which ensures that the linking ligands sufficiently link the non-luminescent quantum dots and the luminescent quantum dots to improve the luminescent performance of the material. In specific examples, the molar ratio of luminescent quantum dots to linking ligands is 1:1, 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, or 1: 100.
Based on the above technical solution, a second aspect of the embodiments of the present application provides a method for preparing the above composite material, as shown in fig. 1, including the following steps:
s01, providing luminescent quantum dots, non-luminescent quantum dots, a connecting ligand and an acid;
and S02, mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid and the connecting ligand in a solvent to obtain the composite material.
The kinds, the amounts and the effects of the luminescent quantum dots, the non-luminescent quantum dots and the linking ligands in step S01 are the same with reference to the luminescent quantum dots, the non-luminescent quantum dots and the linking ligands in the composite material.
The acid is used for eliminating the defect state on the surface of the luminescent quantum dot and the non-luminescent quantum dot so as to promote the connecting ligand to respectively connect the luminescent quantum dot and the non-luminescent quantum dot, thereby effectively connecting the luminescent quantum dot and the non-luminescent quantum dot. The acid includes, but is not limited to, organic acids and inorganic acids, and in some embodiments, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid, and the inorganic acids are more effective in eliminating defect states on the surface of the quantum dot. In further examples, the molar ratio of acid to the sum of luminescent and non-luminescent quantum dots is (0.1-2): 10. In particular embodiments, the molar ratio of acid to the sum of luminescent and non-luminescent quantum dots is 0.1:10, 1:70, 0.2:10, 0.4:10, 0.6:10, 2.5:36, 1:10, 3:21, 1.6:10, 1.8:10, or 2: 10.
In step S02, the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand are mixed in a solvent so that the linking ligand links the luminescent quantum dots and the non-luminescent quantum dots, thereby obtaining the composite material.
In some embodiments, the composite material is prepared by a method further illustrated in fig. 2. The method comprises the following steps of mixing luminescent quantum dots, non-luminescent quantum dots, acid and a connecting ligand in a solvent:
s021, adding the luminescent quantum dots, the acid and the connecting ligand into a solvent, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours to obtain a first solution;
s022, adding non-luminescent quantum dots into the first solution, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours.
On the basis that the connecting ligand is mercaptoalkanoic acid, the luminescent quantum dot, the acid and the connecting ligand are mixed and stirred firstly, and then the non-luminescent quantum dot is added, so that the mercapto end with stronger coordination capacity in the connecting ligand is preferentially coordinated with the metal atom on the surface of the luminescent quantum dot, and the carboxyl end with weaker coordination capacity is coordinated with the metal atom on the surface of the non-luminescent quantum dot, and the luminescent quantum dot and the non-luminescent quantum dot are effectively connected. Meanwhile, by adjusting the temperature and time of mixing and stirring within the above ranges, the reaction efficiency can be effectively improved while the connection of the luminescent quantum dots and the non-luminescent quantum dots by the connecting ligand is promoted.
On the basis of the above embodiment, the light-emitting quantum dots are two-dimensional nano quantum dots. At this time, the non-light emitting quantum dots may be zero-dimensional quantum dots or two-dimensional nano-quantum dots. In some embodiments, the non-luminescent quantum dot is a zero-dimensional quantum dot, the two-dimensional nano quantum dot has a heavier mass than the zero-dimensional quantum dot, the thiol end with strong coordination ability is combined with a luminescent quantum dot with a relatively heavier mass, and the carboxyl end with weaker coordination ability is combined with a non-luminescent quantum dot with a relatively lighter mass, so that the quantum dot can be effectively prevented from falling off from a connecting ligand, and the good stability of the composite material is ensured.
Among them, the solvent is preferably a non-polar solvent so that the luminescent quantum dots and the non-luminescent quantum dots have good dispersion properties in a solution. In some embodiments, the solvent is selected from at least one of chloroform, chlorobenzene, toluene, n-hexane, cyclohexane, n-octane, and n-butane.
In step S022, a second mixed solution is obtained by mixing and stirring at 80 ℃ to 200 ℃ for 10 minutes to 12 hours, and the composite material is dispersed in the second mixed solution.
In order to collect the composite material in the second solution, after the luminescent quantum dots, the non-luminescent quantum dots, the acid and the connecting ligand are mixed in the solvent, solid-liquid separation is further performed on the second solution. In some embodiments, after the step of subjecting the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand to the mixing treatment in the solvent, a precipitant is added to the product of the mixing treatment to precipitate the target product. In some embodiments, after the step of subjecting the luminescent quantum dots, the non-luminescent quantum dots, the acid, and the linking ligand to a mixing treatment in a solvent, the product of the mixing treatment is subjected to an annealing treatment.
Based on the foregoing technical solution, a third aspect of the embodiments of the present application provides a light emitting diode, as shown in fig. 3, including: an anode 1, a light-emitting layer 3 and a cathode 5, wherein the anode 1 and the cathode 5 are oppositely arranged, the light-emitting layer 3 is arranged between the anode 1 and the cathode 5, and furthermore, the material of the light-emitting layer 3 comprises: the composite material or the composite material prepared by the preparation method.
The thickness of the light-emitting layer can be determined by conventional techniques in the art, and in some embodiments, the thickness of the light-emitting layer is from about 5nm to about 100 nm.
The structure of the light emitting diode of the present application can refer to the conventional technology in the art, and in some embodiments, the light emitting diode is an upright structure, and an anode is connected with a substrate as a bottom electrode; in other embodiments, the light emitting diode is an inverted structure, and the cathode is connected to the substrate as a bottom electrode. Further, in addition to the above-described basic functional film layers such as the cathode, the anode, and the light-emitting layer, a hole functional layer such as a hole injection layer, a hole transport layer, and a hole blocking layer may be provided between the anode and the light-emitting layer, and an electron functional layer such as an electron injection layer, an electron transport layer, and an electron blocking layer may be provided between the light-emitting layer and the cathode.
In some embodiments, as shown in fig. 4, the light emitting diode includes: the organic electroluminescent device comprises an anode 1, a hole injection layer 21, a hole transport layer 22, a light-emitting layer 3, an electron transport layer 4 and a cathode 5, wherein the anode 1 is connected with a substrate as a bottom electrode, the hole injection layer 21 is arranged between the anode 1 and the light-emitting layer 3, the hole transport layer 22 is arranged between the hole injection layer 21 and the light-emitting layer 3, and the electron transport layer 4 is arranged between the light-emitting layer 3 and the cathode 5.
In the light emitting diode, materials of the anode, the hole injection layer, the hole transport layer, the light emitting layer, the electron transport layer and the cathode and thicknesses thereof may be referred to in the conventional art.
The substrate includes a rigid substrate and a flexible substrate, and in some embodiments, the substrate is selected from at least one of glass, silicon wafer, polycarbonate, polymethylmethacrylate, polyethylene terephthalate, polyethylene naphthalate, polyamide, and polyethersulfone.
The anode includes a conductive metal including, but not limited to, nickel, platinum, vanadium, chromium, copper, zinc, gold, and the like, or an alloy thereof, and/or a conductive metal oxide including, but not limited to, zinc oxide, indium oxide, tin oxide, Indium Tin Oxide (ITO), Indium Zinc Oxide (IZO), fluorine-doped tin oxide, and the like.
The material of the hole injection layer is selected to be a material with good hole injection performance, including but not limited to poly (3, 4-ethylenedioxythiophene) -polystyrene sulfonic acid (PEDOT: PSS), copper phthalocyanine (CuPc), 2,3,5, 6-tetrafluoro-7, 7',8,8' -tetracyanoquinodimethane (F4-TCNQ), 2,3,6,7,10, 11-hexacyano-1, 4,5,8,9, 12-Hexaazatriphenylene (HATCN), doped or undoped transition metal oxide, doped or undoped metal chalcogenide compound, etc.; wherein the transition metal oxide includes, but is not limited to, MoO3、VO2、WO3CuO, etc., metal sulfur based compounds including but not limited to MoS2、MoSe2、WS2、WSe2CuS, and the like. The thickness of the hole injection layer is preferably 10 to 150 nm.
The material of the hole transport layer is selected as an organic material having good hole transport ability, including but not limited to Poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (TFB), Polyvinylcarbazole (PVK), Poly (N, N 'bis (4-butylphenyl) -N, N' -bis (phenyl) benzidine) (Poly-TPD), Poly (9, 9-dioctylfluorene-CO-bis-N, N-phenyl-1, 4-Phenylenediamine) (PFB), 4',4 ″ -tris (carbazol-9-yl) triphenylamine (TCTA), 4' -bis (9-Carbazole) Biphenyl (CBP), N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine (TPD), N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (NPB), doped graphene, undoped graphene, C60, and the like. The thickness of the hole transport layer is preferably 10 to 150 nm.
The material of the electron transport layer is selected to have good electron transport properties, including but not limited to ZnO, TiO2、Alq3、SnO、ZrO、AlZnO、ZnSnO、BCP、TAZ、PBD、TPBI、Bphen、CsCO3And the like. The thickness of the electron transport layer is preferably 10 to 100 nm.
The cathode may be selected from a single metal or an alloy thereof, including but not limited to at least one of magnesium, calcium, sodium, potassium, titanium, indium, yttrium, lithium, gadolinium, aluminum, silver, tin, lead, cesium, barium; alternatively, the cathode is selected to be a multilayer structure material including, but not limited to, alkali metal halides, alkaline earth metal halides, alkali metal oxides, and the like; alternatively, the cathode is selected as a multi-layered structure material and combined with a metal layer selected as an alkaline earth metal and/or a group 13 metal, including but not limited to LiF/Al, LiO2Al, LiF/Ca, Liq/Al, and BaF2Ca, etc.
In order that the details of the above-described implementations and operation of the present application will be clearly understood by those skilled in the art, and the advanced nature of the composite material and method of making the same of the examples of the present application will be apparent, the practice of the present application will now be illustrated by way of example.
Example 1
In the embodiment, a composite material is prepared by taking CdSe/CdS two-dimensional nano quantum dots, CdS quantum dots and 11-mercaptoundecanoic acid as raw materials, and the specific preparation method is as follows:
1) the light-emitting quantum dots are selected as CdSe/CdS two-dimensional nanometer quantum dots with the peak wavelength of emitted light of 511nm, the length of 30nm, the width of 3nm, the thickness of 2nm and the solution quantum yield of 80%;
adding the luminescent quantum dots, 20% hydrochloric acid and 11-mercaptoundecanoic acid into n-hexane, and mixing and stirring at 80 ℃ for 30mins to obtain a first mixed solution; wherein the mixing molar ratio of the luminescent quantum dots to the 11-mercaptoundecanoic acid in the first mixed solution is 1: 5; the molar ratio of the hydrochloric acid to the luminescent quantum dots is 3: 1.
2) selecting non-luminescent quantum dots as CdS quantum dots with the particle size of 5nm, adding the non-luminescent quantum dots into the first mixed solution prepared in the step 1), mixing and stirring at 100 ℃ for 60mins to obtain a second mixed solution, wherein a composite material is dispersed in the second mixed solution, and the mixing mass ratio of the non-luminescent quantum dots to the luminescent quantum dots is 20: 1;
after stirring is finished, adding n-hexane into the mixed and stirred product to dissolve, adding ethyl acetate and ethanol to precipitate and separate out the composite material, centrifuging, drying, and preparing the dried product into a composite material solution with the mass concentration of 20 mg/mL.
3) Spin-coating the composite material solution obtained in the step 2) on a quartz glass sheet to form a thin film.
Example 2
This example is essentially the same as example 1, except that: the connecting ligand is selected from 5-mercaptopentanoic acid; the mixing molar ratio of the luminescent quantum dots and the 5-mercaptopentanoic acid in the first mixed solution is 1: 10; the mixing mass ratio of the non-luminescent quantum dots to the luminescent quantum dots in the second mixed solution was 30: 1.
example 3
This example is essentially the same as example 1, except that: the connecting ligand is selected from 8-mercapto octanoic acid; the mixing molar ratio of the luminescent quantum dots and the 8-mercapto octanoic acid in the first mixed solution is 1: 20; the molar ratio of the hydrochloric acid to the luminescent quantum dots is 2.5: 1; the mixing mass ratio of the non-luminescent quantum dots to the luminescent quantum dots in the second mixed solution is 35: 1.
example 4
This example is essentially the same as example 1, except that: the connecting ligand is selected from 7-mercaptoheptanoic acid; the mixing molar ratio of the luminescent quantum dots to the 7-mercaptoheptanoic acid in the first mixed solution is 1: 50; the molar ratio of the hydrochloric acid to the luminescent quantum dots is 1: 10; the mixing mass ratio of the non-luminescent quantum dots to the luminescent quantum dots in the second mixed solution is 60: 1.
comparative example 1
The film is prepared by CdSe/CdS two-dimensional nano quantum dots in the comparative example, and the specific preparation method is as follows:
1) the quantum dots are selected as CdSe/CdS two-dimensional nano quantum dots with the peak wavelength of emitted light of 511nm, the length of 30nm, the width of 3nm, the thickness of 2nm and the solution quantum yield of 80%;
2) dispersing the quantum dots into n-octane, and fully and uniformly mixing to form a quantum dot solution with the mass concentration of 20 mg/mL;
3) and (3) spin-coating the quantum dot solution prepared in the step 2) on a quartz glass sheet to form a film.
Example 5
The embodiment provides a light emitting diode, and a preparation method thereof comprises the following steps: an anode, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer and a cathode are sequentially deposited on a substrate. Wherein the substrate is a glass substrate; the bottom electrode is ITO with the thickness of 100 nm; PSS, the thickness of the hole injection layer is 40 nm; the hole transport layer is TFB and has the thickness of 100 nm; the light-emitting layer is the film prepared in the example 1 and has the thickness of 100 nm; the electron transmission layer is ZnO with the thickness of 40 nm; the top electrode was Al and the thickness was 50 nm.
Example 6
This example is essentially the same as example 5, except that: the light-emitting layer was the thin film prepared in example 2.
Example 7
This example is essentially the same as example 5, except that: the light-emitting layer was the film prepared in example 3.
Example 8
This example is essentially the same as example 5, except that: the light-emitting layer was the film prepared in example 4.
Comparative example 2
This comparative example was prepared essentially identically to example 5, except that: the light-emitting layer was the film prepared in comparative example 1.
The films prepared in examples 1 to 4 and comparative example 1 were subjected to quantum yield tests, and quantum yield measurements were performed on film samples using an Edinburgh FLS980 fluorescence spectrometer coupled with a photoluminescence quantum yield attachment to obtain the results in Table 1.
TABLE 1
| Comparative example 1 | Example 1 | Example 2 | Example 3 | Example 4 | |
| Thin film quantum yield | 20％ | 34％ | 40％ | 31％ | 33％ |
The external quantum dot efficiency (EQE) of each of the light emitting diodes prepared in examples 5 to 8 was measured using an EQE optical measurement instrument, and the measurement results are shown in table 2.
The specific value of the number of the emitted photons converted from the logarithm of the electron-hole injected into the quantum dot, the unit of which is%, is an important parameter for measuring the quality of the electroluminescent device, and the specific calculation formula of the EQE is as follows:
in the formula etaeFor light output coupling efficiency, ηrIs the ratio of the number of recombination carriers to the number of injection carriers, chi is the ratio of the number of excitons generating photons to the total number of excitons, KRTo the rate of the radiation process, KNRIs the non-radiative process rate.
TABLE 2
| Comparative example 2 | Example 5 | Example 6 | Example 7 | Example 8 | |
| EQE(％) | 1.3 | 2.5 | 3.1 | 3.8 | 3.9 |
It should be understood that the above examples and comparative examples are illustrative and the present application is not limited by the type of the light emitting diode. For example, the result is similar whether the light emitting diode is of an upright type, an inverted type, a top emission type, a bottom emission type, or the like.
The above description is only exemplary of the present application and should not be taken as limiting the present application, as any modification, equivalent replacement, or improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.
Claims (10)
1. A composite material comprising luminescent quantum dots, non-luminescent quantum dots, and linking ligands, the linking ligands linking the luminescent quantum dots and the non-luminescent quantum dots.
2. The composite material of claim 1, wherein the luminescent quantum dots are two-dimensional nano-quantum dots;
preferably, the non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nano-quantum dots.
3. The composite material of claim 2, wherein the luminescent quantum dot has a core-shell structure, and a shell layer of the luminescent quantum dot is grown in a planar direction thereof;
preferably, the non-light emitting quantum dots connect two planes in the thickness direction of the light emitting quantum dots.
4. The composite material of claim 3, wherein the non-luminescent quantum dots are non-core shell structured quantum dots;
the metal element of the non-luminous quantum dot is in the same family as the metal element of the shell layer of the luminous quantum dot, and/or the non-metal element of the non-luminous quantum dot is in the same family as the non-metal element of the shell layer of the luminous quantum dot;
preferably, the shell material of the luminescent quantum dot is II-VI group semiconductor material, and the core material of the luminescent quantum dot is II-VI group semiconductor material or III-V group semiconductor material;
preferably, the material of the non-luminescent quantum dots is a II-VI semiconductor material.
5. The composite material of claim 1, wherein the linking ligand comprises a first linking group for linking the luminescent quantum dots and a second linking group for linking the non-luminescent quantum dots, the first linking group and the second linking group each being independently selected from any one of a mercapto group, a carboxyl group, a hydroxyl group, a sulfonic group, an amino group, and a phosphoric group;
preferably, the linking ligand is a mercaptoalkanoic acid.
6. The composite material of any one of claims 1 to 5, wherein the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1 (10-100); and/or
The molar ratio of the luminescent quantum dots to the connecting ligand is 1 (1-100).
7. A preparation method of a composite material is characterized by comprising the following steps:
providing luminescent quantum dots, non-luminescent quantum dots, a linking ligand and an acid;
and mixing the luminescent quantum dots, the non-luminescent quantum dots, the acid and the connecting ligand in a solvent to obtain the composite material.
8. The method of claim 7, wherein the step of subjecting the luminescent quantum dot, the non-luminescent quantum dot, the acid, and the linking ligand to a mixing treatment in a solvent comprises:
adding the luminescent quantum dots, the acid and the connecting ligand into a solvent, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours to obtain a first solution;
adding the non-luminescent quantum dots into the first solution, and mixing and stirring at 80-200 ℃ for 10 minutes to 12 hours.
9. The method of claim 8, wherein the luminescent quantum dot is a two-dimensional nano quantum dot;
preferably, the non-luminescent quantum dots are zero-dimensional quantum dots or two-dimensional nano-quantum dots;
preferably, the molar ratio of the acid to the sum of the luminescent quantum dots and the non-luminescent quantum dots is (0.1-2): 10;
preferably, the mass ratio of the luminescent quantum dots to the non-luminescent quantum dots is 1 (10-100);
preferably, the acid is selected from at least one of hydrochloric acid, hydrofluoric acid, nitric acid, and sulfuric acid;
preferably, the connecting ligand is selected from mercaptoalkanoic acid, and the molar ratio of the luminescent quantum dot to the connecting ligand is 1 (1-100);
preferably, the solvent is selected from at least one of chloroform, chlorobenzene, toluene, n-hexane, cyclohexane, n-octane, and n-butane.
10. A light emitting diode comprising a light emitting layer, the material of the light emitting layer comprising: a composite material according to any one of claims 1 to 6 or a composite material produced by the production method according to any one of claims 7 to 9.
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