CN112625688B - Core-shell quantum dot, preparation method thereof, composition and electroluminescent device containing core-shell quantum dot - Google Patents

Core-shell quantum dot, preparation method thereof, composition and electroluminescent device containing core-shell quantum dot Download PDF

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CN112625688B
CN112625688B CN201910907465.8A CN201910907465A CN112625688B CN 112625688 B CN112625688 B CN 112625688B CN 201910907465 A CN201910907465 A CN 201910907465A CN 112625688 B CN112625688 B CN 112625688B
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叶荣琴
陈小朋
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Najing Technology Corp Ltd
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Abstract

The invention provides a core-shell quantum dot, a preparation method thereof and an electroluminescent device containing the same. The preparation method comprises the steps of firstly mixing CdSe cores with a first VI group element precursor, and then regulating and controlling Cd by adding the first cadmium precursor at a constant speed x ‑Zn 1‑x The proportion of Cd and VI group elements of each single shell layer in the-VI layer realizes the synthesis of green quantum dots doped with shells with different Cd contents, and finally the CdSe/Cd is obtained by synthesis x ‑Zn 1‑x ‑VI/Cd y ‑Zn 1‑y -VI quantum dots. Because each single shell layer is uniformly doped with Cd in the coating process, the valence band energy level of the quantum dot can be effectively regulated, the injection energy barrier of electrons and holes of the quantum dot in the working process of the electroluminescent device is reduced, and the performance of the electroluminescent device is further improved.

Description

Core-shell quantum dot, preparation method thereof, composition and electroluminescent device containing core-shell quantum dot
Technical Field
The invention relates to the field of quantum dot luminescent materials, in particular to a core-shell quantum dot, a preparation method and a composition thereof, and an electroluminescent device containing the core-shell quantum dot.
Background
Quantum Dot (QD), i.e. semiconductor nanocrystals typically between 1 and 100nm in size and having Quantum confinement effects. Due to its special optical and optoelectronic properties, such as extremely broad absorption spectrum, very narrow emission spectrum, very high luminous efficiency, the electrical and optical properties, etc. of the quantum dots can be significantly adjusted by adjusting their respective bandgaps by adjusting their dimensions, thus the photophysical stability of inorganic materials is better than that of organic luminescent materials.
In recent years, quantum dots are used as inorganic light-organic ligand materials, and have the advantages of extremely narrow emission spectrum, better inorganic material stability and the like compared with organic light-emitting materials, so that quantum dot light-emitting diode (QLED) display technology based on quantum dot materials has longer device service life and better luminescent color purity, and the application prospect in the display field is widely focused.
In the prior literature report, for green CdSe@ZnS alloy quantum dots, the transmission rate of electrons in the quantum dots is reduced by increasing the thickness of a ZnSe layer in a shell layer, so that the development of a long-service-life green quantum dot light emitting diode (G-QLED) is realized, and the quantum dotsThe device result was 100cd m -2 At brightness T 50 The service life is 90,000 hours, znS is taken as an outer shell layer, the photo-bleaching resistance and the air stability of the ZnS shell layer are correspondingly improved, however, the ZnS shell layer has higher electron and hole injection energy barriers due to higher valence bands, so that the effective injection of electrons and holes is prevented; later, the document also reports that QLED developed by green quantum dot based on ZnSe as a shell layer, and the device result is 100cd m -2 At brightness T 50 The service life can reach 1760000h, although the half-width of the quantum dot material is below 25nm, the outermost layer of the quantum dot material is a ZnSe layer, so that the quantum dot material is poor in air stability and photo-bleaching resistance, the quantum efficiency is easy to drop, the solid state quantum efficiency and the fluorescence lifetime are reduced when the quantum dot is formed into a film, the requirements and the cost of the QLED device for equipment are greatly increased, and the commercialization requirements cannot be met.
From the existing researches, it is shown that the quantum dots with core-shell structures such as CdSe/ZnSe, cdSe/CdS, cdSe/ZnS and the like cannot meet various basic requirements of QLEDs on the quantum dots, such as high quantum efficiency, photo-bleaching resistance, high stability, narrow half-peak width and the like. For the quantum dots with alloy structures in the prior art, such as CdSe@ZnS and CdSe@ZnS/ZnS, the External Quantum Efficiency (EQE) of the device is higher (more ideal device structure, EQE can reach more than 15% and even approach 20%), but the service life of the device is generally low, and the requirements of commercial application cannot be met.
Moreover, the existing research shows that the luminescence wavelength of the core-shell structure quantum dot which takes CdSe as a core and is doped with Cd in a shell in the prior art is difficult to achieve a green wave band.
Disclosure of Invention
The invention mainly aims to provide a core-shell quantum dot, a preparation method thereof and an electroluminescent device containing the core-shell quantum dot, so as to solve the problem that the core-shell quantum dot with Cd core and Cd shell in the prior art cannot realize green luminescence.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for preparing core-shell quantum dots, comprising: step S1, a first zinc precursor, a first VI element precursor and a second VI element precursor are mixed together Mixing a ligand and CdSe core in a first non-coordinating solvent and heating to obtain a first reactant system; step S2, adding a first cadmium precursor into the first reactant system at a constant speed, and coating a CdSe core with a cadmium-doped first Cd x -Zn 1-x Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI quantum dots; step S3, combining a second zinc precursor, a second VI element precursor, a second ligand and CdSe/Cd x -Zn 1-x -mixing and heating VI quantum dots in a second non-coordinating solvent to obtain a second reactant system, wherein the second group VI element precursor is different from the first group VI element precursor; step S4, adding a second cadmium precursor into the second reactant system at a constant speed, wherein the second cadmium precursor is CdSe/Cd x -Zn 1-x Cladding cadmium ion doped second Cd on-VI quantum dot y -Zn 1-y Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI/Cd y -Zn 1-y -VI quantum dots, wherein X is more than 0 and less than or equal to 0.1, and Y is more than 0 and less than or equal to 0.1.
Further, step S1 includes: step S11, mixing and heating a first zinc precursor, a CdSe core, a first ligand and a first non-coordinating solvent to obtain a first mixed solution; and step S12, adding the first VI element precursor into the first mixed solution under the heating condition to react to obtain a first reactant system, wherein the reaction time in the step S12 is preferably 20S-5 min.
Further, step S3 includes: step S31, second zinc precursor, second ligand, cdSe/Cd x -Zn 1-x Mixing and heating the VI quantum dots and a second non-coordinating solvent to obtain a second mixed solution; and step S32, adding the second VI element precursor into the second mixed solution under the heating condition to react to obtain a second reactant system, wherein the reaction time of the step S32 is preferably 20S-5 min.
Further, the first cadmium precursor and/or the second cadmium precursor are added at a uniform rate of 5X 10 per one mole of CdSe core 3 ～1×10 5 Preferably, the uniform speed addition is dropwise addition, and the duration of the dropwise addition is 1-30 min.
Further, the reaction temperatures of step S1 to step S4 are independently selected from any one of temperatures of 250 to 310 ℃.
Further, the molar ratio of Cd in the first cadmium precursor, zn in the first zinc precursor and free first ligand is 1:1:10-1: 200:500, the molar ratio of Cd in the second cadmium precursor, zn in the second zinc precursor and free second ligand is 1:1:10-1:200:500.
Further, the first group VI element precursor is a Se precursor or a mixed precursor of Se and S, the second group VI element precursor is an S precursor, and the first zinc precursor and the second zinc precursor are the same or different; preferably, when the first group VI element precursor is a mixed precursor of Se and S, the molar ratio of Se precursor and S precursor is 1 or more.
Further, the first exciton peak of the CdSe core is selected from 495 to 545nm.
According to another aspect of the present invention, there is provided a core-shell quantum dot whose core is CdSe and whose shell layer includes Cd x -Zn 1-x -VI shell and Cd-coated x -Zn 1-x Cd of the-VI shell y -Zn 1-y The VI shell layer is more than 0 and less than or equal to 0.1, Y is more than 0 and less than or equal to 0.1, and the peak emission wavelength of the core-shell quantum dot is 500-550 nm.
Further, the half-width of the core-shell quantum dot is below 25nm, the quantum efficiency of the core-shell quantum dot is 80-100%, and the quantum efficiency of the core-shell quantum dot is preferably 90-100%.
According to another aspect of the present invention, there is also provided a quantum dot composition, the quantum dot composition comprising core-shell quantum dots, the core-shell quantum dots being prepared by the above preparation method, or the core-shell quantum dots being the above core-shell quantum dots.
According to another aspect of the present invention, there is also provided a quantum dot light emitting device, the quantum dot light emitting device including a core-shell quantum dot, the core-shell quantum dot being prepared by the above preparation method, or the core-shell quantum dot being the above core-shell quantum dot.
By applying the technical scheme of the invention, the invention provides a preparation method of the core-shell quantum dot, which comprises the steps of firstly preparing a CdSe core, a first zinc precursor and a first VI group element precursor (such as a core-shell quantum dot containing The Se anions or the mixed anions of Se and S are mixed, and then the Cd is regulated and controlled by adding the first cadmium precursor (containing Cd cations) at a constant speed x -Zn 1-x The proportion of Cd and VI group elements of each single shell layer in the VI layer is regulated and controlled by adopting a mode of adding a second zinc precursor firstly and then adding a second cadmium precursor at uniform speed y -Zn 1-y The proportion of Cd and VI group elements of each single shell layer in the-VI layer realizes the synthesis of green quantum dots doped with shells with different Cd contents, and finally the CdSe/Cd is obtained by synthesis x -Zn 1-x -VI/Cd y -Zn 1-y VI quantum dots (e.g. CdSe/Cd x Zn 1- x SeS/Cd Y Zn 1-Y S or CdSe/Cd x Zn 1-x Se/Cd Y Zn 1-Y Green quantum dots with Cd doped S shell). In addition, as the Cd in the reaction system can play a role in limiting speed, and the Zn in the first zinc precursor added at one time is excessive compared with the Cd in the first cadmium precursor added at a later time at a constant speed, the Cd added in unit time is fixed through the constant speed addition, so that the amount of the decomposed anions is also fixed, the proportion of the anions in the shell layers is uniform, namely, each single shell layer is uniformly doped with Cd element in the coating process. The shell layer with uniform Cd doping can effectively regulate and control the valence band energy level of the quantum dot, reduce the injection energy barrier of electrons and holes of the quantum dot when the electroluminescent device works, and further improve the performance of the electroluminescent device, and experiments show that the core-shell quantum dot obtained by the preparation method is applied to the luminescent device, and the EQE is more than 10 percent and 100Cd m -2 T of brightness 50 The service life is more than 10,000 hours.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
fig. 1 shows an SEM image of the quantum dot core prepared in example 1 of the present invention;
fig. 2 shows SEM images of the quantum dot cores prepared in examples 2 and 19 of the present invention;
fig. 3 shows an SEM image of the quantum dot core prepared in example 3 of the present invention;
fig. 4 shows SEM images of the quantum dot cores prepared in comparative example 1 of the present invention;
fig. 5 shows an SEM image of the quantum dot core prepared in example 7 of the present invention.
Detailed Description
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other. The invention will be described in detail below with reference to the drawings in connection with embodiments.
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate in order to describe the embodiments of the invention herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
As described in the background art, the prior art shows that the peak luminescence wavelength of the core-shell structure quantum dot which takes CdSe as a core and is doped with Cd in a shell in the prior art is difficult to achieve a green wave band. The inventor of the present invention provides a preparation method of a core-shell quantum dot, aiming at the above technical problems, including:
step S1, mixing and heating a first zinc precursor, a first VI element precursor, a first ligand and a CdSe core in a first non-coordinating solvent to obtain a first reactant system;
Step S2, adding a first cadmium precursor into the first reactant system at a constant speed, and coating a CdSe core with a cadmium-doped first Cd x -Zn 1-x Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI quantum dots;
step S3, combining a second zinc precursor, a second VI element precursor, a second ligand and CdSe/Cd x -Zn 1-x -mixing and heating VI quantum dots in a second non-coordinating solvent to obtain a second reactant system, wherein the second group VI element precursor is different from the first group VI element precursor;
step S4, adding a second cadmium precursor into the second reactant system at a constant speed, wherein the second cadmium precursor is CdSe/Cdx-Zn 1-x Cladding cadmium ion doped second Cd on-VI quantum dot y -Zn 1-y Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI/Cd y -Zn 1-y -VI quantum dots,
wherein X is more than 0 and less than or equal to 0.1, Y is more than 0 and less than or equal to 0.1.
Since Cd cations are more reactive than Zn cations, se anions preferentially combine with Cd cations to form CdSe when the two are simultaneously in a reaction system, and the Cd is regulated by firstly mixing a CdSe core with a first zinc precursor and a first VI element precursor (such as a precursor containing Se anions or Se and S mixed anions) and then adding the first cadmium precursor (containing Cd cations) at a constant speed x -Zn 1-x The proportion of Cd and VI group elements of each single shell layer in the VI layer is regulated and controlled by adopting a mode of adding a second zinc precursor firstly and then adding a second cadmium precursor at uniform speed y -Zn 1-y The proportion of Cd and VI group elements of each single shell layer in the VI layer is changed, so that the synthesis of the green quantum dots doped with the shells with different Cd contents is realized by the mode of firstly injecting anions and then adding Cd cations at constant speed, and finally, C is obtained by synthesisdSe/Cd x -Zn 1-x -VI/Cd y -Zn 1-y VI quantum dots (e.g. CdSe/Cd x Zn 1-x SeS/Cd Y Zn 1-Y S or CdSe/Cd x Zn 1-x Se/Cd Y Zn 1-Y The green quantum dot doped with Cd in the S shell layer) effectively solves the problem that the green quantum dot is difficult to synthesize in the existing synthesis scheme in which Cd and Zn precursors exist in a system and then anion precursors are injected.
In addition, as the Cd in the reaction system can play a role in limiting speed, and the Zn in the first zinc precursor added at one time is excessive compared with the Cd in the first cadmium precursor added at a later time at a constant speed, the Cd added in unit time is fixed through the constant speed addition, so that the amount of the decomposed anions is also fixed, the proportion of the anions in the shell layers is uniform, namely, each single shell layer is uniformly doped with Cd element in the coating process. The shell layer with uniform Cd doping can effectively regulate and control the valence band energy level of the quantum dot, reduce the injection energy barrier of electrons and holes of the quantum dot when the electroluminescent device works, and further improve the performance of the electroluminescent device, and experiments show that the core-shell quantum dot obtained by the preparation method is applied to the luminescent device, and the EQE is more than 10 percent and 100Cd m -2 T of brightness 50 The service life is more than 10,000 hours.
Compared with the method of injecting Cd cations once, the method of adding Cd cations at a constant speed reduces the local overlarge concentration of Cd cations brought by the injection once, thereby reducing the generation of CdSe small particles, ensuring the relatively narrow particle size distribution of synthesized quantum dots in the coating process, and further maintaining the half-peak width of the quantum dots, and experiments prove that the half-peak width of the core-shell quantum dots can be below 25nm and the external quantum efficiency can reach 90-100%.
Exemplary embodiments of a method of preparing core-shell quantum dots provided according to the present invention will be described in more detail below. These exemplary embodiments may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It should be appreciated that these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of these exemplary embodiments to those skilled in the art.
First, the above step S1 is performed: the first zinc precursor, the first group VI element precursor, the first ligand and the CdSe core are mixed and heated in a first non-coordinating solvent to obtain a first reactant system. Wherein Zn element in the first zinc precursor is excessive relative to Cd element in the first cadmium precursor which is added at a constant speed in the step S2. After the first cadmium precursor (containing Cd cations) is added at a constant speed in the step S2, the formed quantum dot shell Cd can be ensured x -Zn 1-x The Cd element in the VI is uniformly doped.
In order to enable the core-shell quantum dot to have a green luminescence wavelength, it is preferable that the first exciton peak of the CdSe core is selected from 495 to 545nm.
The first group VI element precursor may be a Se precursor or a mixed precursor of Se and S, and specifically may be selected from any one or more of a non-coordinating solution of selenium, a trialkylphosphine solution of selenium, a non-coordinating solution of selenium and sulfur, and a trialkylphosphine solution of selenium and sulfur; in order to obtain a quantum dot having a uniform Cd doping in the shell layer, a uniform particle size distribution of the quantum dot, a high quantum efficiency, and a high optical stability, it is preferable that when the first group VI element precursor is a mixed precursor of Se and S, the molar ratio of Se precursor and S precursor is 1 or more.
In a preferred embodiment, the step S1 includes: step S11, mixing and heating a first zinc precursor, a CdSe core, a first ligand and a first non-coordination solvent to obtain a first mixed solution, wherein the first zinc precursor is preferably a zinc carboxylate precursor with a carbon chain length of 10-22, and the first ligand can be carboxylic acid with a carbon chain length of 10-22; and step S12, adding the first VI element precursor into the first mixed solution under the heating condition to react, so as to obtain a first reactant system.
In the above preferred embodiment, in order to enhance the reaction efficiency between the first group VI element precursor and the first mixed solution, more preferably, the reaction temperatures in step S11 and step S12 are independently selected from any one of 250 to 310 ℃; and, more preferably, the reaction time in step S12 is 20S to 5min.
After obtaining the first reactant system described above, step S2 is performed: adding a first cadmium precursor into a first reactant system at a constant speed, and coating a CdSe core with a cadmium-doped first Cd x -Zn 1-x Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI quantum dots, wherein X is more than 0 and less than or equal to 0.1, and Y is more than 0 and less than or equal to 0.1.
In the above step S2, in order to raise the first Cd x -Zn 1-x The synthesis efficiency of the VI shell layer, preferably, the first cadmium precursor is added to the first reactant system at a constant rate at a temperature of 250-310 ℃.
In the step S2, the uniform addition means that one solution is added to the other solution at a fixed rate, and in order to improve the uniformity of Cd doping in the shell layer, preferably, the first cadmium precursor is added at a uniform rate of 5×10 per one mole of CdSe core 3 ～1×10 5 mol/h; more preferably, the uniform speed addition is dripping, and the duration of the dripping is 1 min-30 min.
In the step S2, the first cadmium precursor is added to the first reactant system at a constant speed, and in order to obtain the quantum dot with uniformly doped Cd in the shell layer and in the green light range, preferably, the molar ratio of Cd in the first cadmium precursor, zn in the first zinc precursor and free first ligand is 1:1:10-1:200:500, and the molar ratio of Zn in the first zinc precursor and first group VI element precursor is 2:1-12:1.
It should be noted that, for the ratio of the mole numbers of Cd in the first cadmium precursor, zn in the first zinc precursor, and the first ligand to the total amount required for each substance reaction, the first ligand reacts with the first zinc precursor to allow a part of the ligand to bind to zinc, and the remaining first ligand is free first ligand, so the mole number of the first ligand is understood to be the mole number of the free first ligand solvent after removing a part of the reaction with Zn, such as OA, where a part forms Zn (OA) 2 The remaining other fraction was free OA, and the molar ratio was calculated from the molar number of this fraction.
After obtaining CdSe/Cd x -Zn 1-x After the VI quantum dots, step S3 is performed: combining a second zinc precursor, a second group VI element precursor, a second ligand, and CdSe/Cd x -Zn 1-x -VI quantum dots are mixed and heated in a second non-coordinating solvent to obtain a second reactant system, wherein the second group VI element precursor is different from the first group VI element precursor. Wherein Zn element in the second zinc precursor is excessive relative to Cd element in the second cadmium precursor added at a uniform speed in the step S4. After the second cadmium precursor (containing Cd cations) is added at a constant speed in the step S2, the formed quantum dot shell Cd can be ensured y -Zn 1-y The Cd element in the VI is uniformly doped.
The first zinc precursor and the second zinc precursor in step S3 may each independently be the same or different zinc precursors; the second group VI element precursor may be an S precursor, and specifically may be selected from any one or more of a non-coordinating solution of sulfur and a trialkylphosphine solution of sulfur.
In a preferred embodiment, the step S3 includes: step S31, second zinc precursor, second ligand, cdSe/Cd x -Zn 1-x -VI quantum dots and a second non-coordinating solvent are mixed and heated to obtain a second mixed solution, the second zinc precursor is preferably a zinc carboxylate precursor with a carbon chain length of 10-22, and the second ligand is preferably a carboxylic acid with a carbon chain length of 10-22; and step S32, adding the second VI element precursor into the second mixed solution under the heating condition to react, so as to obtain a second reactant system.
In the above preferred embodiment, in order to enhance the reaction efficiency between the second group VI element precursor and the second mixed solution, more preferably, the reaction temperatures in step S31 and step S32 are independently selected from any one of 250 to 310 ℃; and, more preferably, the reaction time in step S32 is 20S to 5min.
After obtaining the second reactant system described above, step S4 is performed: adding a second cadmium precursor to the second reactant system at a constant rate and at a CdSe/Cd ratio x -Zn 1-x Cladding cadmium ion doped second Cd on-VI quantum dot y -Zn 1-y Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI/Cd y -Zn 1-y -VI quantum dots, wherein X is more than 0 and less than or equal to 0.1, and Y is more than 0 and less than or equal to 0.1.
In the above step S4, in order to raise the second Cd y -Zn 1-y The synthesis efficiency of the VI shell layer, preferably, the second cadmium precursor is added to the second reactant system at a constant rate at a temperature of 250-310 ℃.
In the step S4, the uniform addition means that one solution is added to the other solution at a fixed rate, and in order to improve the uniformity of Cd doping in the shell layer, preferably, the second cadmium precursor is added at a uniform rate of 5×10 per one mole of CdSe core 3 ～1×10 5 mol/h; more preferably, the uniform speed addition is dripping, and the duration of the dripping is 1 min-30 min.
In the step S4, the second cadmium precursor is added to the second reactant system at a constant speed, and in order to obtain the green quantum dots which are uniformly doped with Cd in the shell layer, have high quantum efficiency and are suitable for the QLED device, preferably, the molar ratio of Cd in the second cadmium precursor, zn in the second zinc precursor and free second ligand (which is the same as the free first ligand and is not repeated) is 1:1:10-1:200:500, and the molar ratio of Zn in the second zinc precursor and the second VI element precursor is 2:1-12:1.
According to another aspect of the present invention, there is provided a core-shell quantum dot, the core of which is CdSe, the quantum dot shell comprises Cd x -Zn 1-x -VI shell and Cd-coated x -Zn 1-x Cd of the-VI shell y -Zn 1-y The VI shell layer is more than 0 and less than or equal to 0.1, Y is more than 0 and less than or equal to 0.1, and the peak emission wavelength of the core-shell quantum dot is 500-550 nm.
As the reactivity of Cd cations is higher than that of Zn cations, se anions can be preferentially combined with Cd cations to generate CdSe when the Cd cations and the Se anions are simultaneously in a reaction system, and the shell layer of the core-shell quantum dot is obtained by adding the Cd cations at a constant speed, so that the prepared Cd is obtained x -Zn 1-x -VI shell and coated Cd x -Zn 1-x Cd of the-VI shell y -Zn 1-y The Cd doping amount in the-VI shell layer is uniform, and the process is finished under the condition of doping more Cd And green core-shell quantum dots can be obtained. According to the invention, cd is doped in each single shell layer, so that the valence band energy level of the device can be effectively regulated and controlled, the injection energy barrier of electrons and holes in the device working process is reduced, and the performance of the electroluminescent device can be further improved.
Compared with the method of injecting Cd cations once, the method of adding Cd cations at a constant speed reduces the local excessive concentration of Cd cations caused by the injection once, reduces the generation of CdSe small particles, ensures that the particle size distribution of the synthesized quantum dots in the coating process is relatively narrow, and thus maintains the half-peak width of the quantum dots.
Experiments prove that the half-peak width of the core-shell quantum dot obtained by the preparation method can be kept below 25nm, and the quantum efficiency can reach 80-100%, even 90-100%.
In the core-shell quantum dot of the invention, the quantum dot shell layer comprises Cd x -Zn 1-x -VI shell and Cd-coated x -Zn 1-x Cd of the-VI shell y -Zn 1-y -VI shell, cd as described above x -Zn 1-x the-VI shell layer may be selected from Cd x1 Zn 1-x1 Se and Cd x1 Zn 1- x1 Any of the SeS, cd as described above y -Zn 1-y the-VI shell layer can be Cd Y1 Zn 1-Y1 S，0＜X 1 ≤0.1，0＜Y 1 ≤0.1。
According to another aspect of the present invention, there is also provided a quantum dot composition, such as a quantum dot ink, comprising a core-shell quantum dot, the core-shell quantum dot being prepared by the above-described preparation method, or the core-shell quantum dot being the above-described core-shell quantum dot.
According to another aspect of the present invention, there is also provided a quantum dot light emitting device, including a core-shell quantum dot, the core-shell quantum dot being prepared by the above preparation method, or the core-shell quantum dot being the above core-shell quantum dot. The quantum dot light-emitting device can be an electroluminescent device or a photoluminescent device. In some embodiments the quantum dot light emitting device is a display device or a lighting device.
The above-described core-shell quantum dot of the present invention and the method of preparing the same will be further described below with reference to examples and comparative examples.
Example 1
The embodiment provides a preparation method of a quantum dot core, which comprises the following steps:
synthesis of CdSe core:
1) 0.533g (2 mmol) of Cd (Ac) was reacted 2 ·2H 2 O, 2.28g (8 mmol) of Oleic Acid (OA) and 12g of Octadecene (ODE) are sequentially weighed and placed in a 100mL three-necked flask, a magneton is added, nitrogen is introduced, the temperature of the system is raised to 170 ℃, and the stirring speed is 60rpm;
2) 39.5mg of selenium powder (Se, 0.5 mmol) was weighed, 2mL of ODE was added, and the mixture was subjected to ultrasonic dispersion treatment for 2min;
3) After deoxidizing the system, raising the temperature of the system to 230 ℃, quickly injecting 1mL Se-ODE, reacting at 220 ℃, monitoring the UV value, and reacting for 15min to obtain a first exciton peak UV=488 nm of CdSe;
4) And dropwise adding 0.1mL of 0.5M Se-ODE in batches, wherein the adding interval is 10min, sampling and monitoring after adding for 5min, stopping the reaction after the UV first exciton peak reaches the target position, and synthesizing CdSe cores with the first exciton peak between 495 and 645nm by the method, wherein the CdSe cores are used for synthesizing green quantum dots.
Purification of quantum dot core:
5) Pouring the prepared CdSe core into a separating funnel, adding 20mL of normal hexane, adding 70mL of methanol, uniformly mixing, removing lower methanol, washing 2-3 times with methanol, and keeping the volume of the upper solution between 10 and 15 mL;
6) Transferring the solution with the CdSe core into a centrifuge tube, adding 30-40mL of acetone, uniformly mixing, centrifuging at 4900rpm for 3min, discarding the liquid solution, and dissolving the solid precipitate with ODE;
7) Centrifuging at 4900rpm for 3min, collecting ODE solution, and measuring the first exciton peak OD.
Example 2
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 Se (under each element in the chemical formula)The scale does not refer to gradual change of elements in the shell layer in the product, but rather refers to initial proportion and final proportion change of the elements in the shell layer and total cations of the shell layer; in this example, the molar number of Cd is 1.2mL/h×0.2M×6 min=0.024 mmol, the molar number of Se is 1mL×0.5 M=0.5 mmol, the anionic and cationic reactions are equal substances, the molar number of Zn participating in the reaction is the molar number of Se minus the molar number of Cd, and 0.476mmol, since Cd ions gradually react into the shell layer in a dropwise manner, zn ions are always present in the reaction system, and the reactivity of Cd ions is higher than that of Zn ions, the Cd ions preferentially react with anions. Therefore, in the shell layer, the initial proportion of Cd is 0, the final proportion of Cd is 0.024/0.5=0.05, the initial proportion of Zn is 1, the final proportion of Zn is 0.476/0.5=0.95, and the following examples are calculated in the same manner, and are not repeated), the preparation method of the core-shell quantum dot comprises the following steps:
1) 550mg (3 mmol) of zinc acetate Zn (Ac) 2 3.45g (12 mmol) of OA and 10g of ODE are weighed in sequence and placed in a three-mouth bottle with 0.1L, a magnet is added, nitrogen is introduced, the temperature is increased to 180 ℃, the stirring speed is 60rpm, and the nitrogen is introduced to discharge air and acetic acid for at least 0.5h;
2) Weighing 0.5mmol of Se powder, adding 1mL of TBP ligand solvent for ultrasonic treatment to dissolve the Se powder;
3) After the system was deoxygenated, the temperature was raised to 305 ℃, cdSe cores obtained by the preparation method in example 1 were added, the first exciton peak uv=495 nm, od=50, 25nmol;
4) Injecting 1mL of 0.5M Se-TBP prepared in the step 2);
5) Step 4) after 1min of reaction, 0.2M Cd (OA) was added dropwise at a dropping rate of 1.2mL/h 2 (1.2mL/h×0.2M＝0.24mmol/h，0.24mmol/h÷25nmol＝9.6×10 3 mol/h, cd (OA) under the condition of calculating one mole of quantum dot core 2 The drop velocity of (2) was 9.6X10 3 mol/h), dropwise adding for 6min, and reacting at 300 ℃;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent OA is 1:125:250 (ligand solvents used herein are understood to remove Zn to form Zn (OA) with Zn) 2 Mole number of free OA after a part of the reaction, zn (Ac) in this example 2 3mmol,6mmol of OA with Zn will form Zn (OA) 2 There is still 6mmol of OA remaining; cd (OA) used herein 2 The mole number of Cd in the system is calculated by the mole total amount of quantum dot cores in the system, and is not Cd (OA) under the condition of one mole of quantum dot cores 2 Calculated based on the drop velocity of (2), cd (OA) was used in this example based on the total molar amount of quantum dot nuclei added 2 The drop rate of (2) was 1.2mL/h, and Cd (OA) was calculated 2 The molar number of Cd was 1.2 mL/h.times.0.2Mtimes.6min=0.024 mmol, cd (OA) used in each of the following examples 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and the ligand solvent OA is calculated in the same way, and is not repeated;
6) After the dripping is finished, stopping the reaction, cooling to below 100 ℃, transferring the prepared core-shell quantum dots into a 50mL centrifuge tube, adding 30mL of acetone, uniformly mixing, centrifuging at 4900rpm for 3min, discarding the liquid solution, airing the solid, and dissolving with n-hexane.
Example 3
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot comprises the following steps:
(1)Cd 0→0.1 Zn 1→0.9 the coating of Se layer was performed in the same manner as in example 2, with the difference from example 2 that:
in step 3), the CdSe core has uv=505nm, od=50, 25nmol;
in step 5), 0.2M Cd (OA) 2 The drop rate of (A) is 2mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 The drop velocity of (2) was 1.6X10 4 mol/h), the dropwise adding duration is 7.5min;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent is 1:60:120.
(2)Cd 0→0.1 Zn 1→0.9 coating of S layer：
1) 275mg (1.5 mmol) of zinc acetate Zn (Ac) 2 Sequentially weighing 1.7g (6 mmol) of OA and 5g of ODE, placing into a three-mouth bottle of 0.1L, adding a magnet, introducing nitrogen, heating to 180 ℃, stirring at 60rpm, and introducing nitrogen to discharge air and acetic acid for at least 0.5h;
2) Weighing 0.5mmol of S powder, adding 1mL of TBP for ultrasonic treatment to dissolve the S powder;
3) After deoxidizing the system, the temperature is increased to 300 ℃, and CdSe/Cd synthesized in the step (1) is added 0→0.1 Zn 1→ 0.9 Se QD；
4) Injecting the S-TBP prepared in the step 2);
5) After 1min of reaction, 0.2M Cd (OA) was added dropwise at a dropping rate of 1mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 8X 10 3 mol/h), the dripping duration is 15min;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent is 1:30:60;
6) After the dripping is finished, stopping the reaction, cooling to below 100 ℃, transferring the prepared core-shell quantum dots into a 50mL centrifuge tube, adding 30mL of acetone, uniformly mixing, centrifuging at 4900rpm for 3min, discarding the liquid solution, airing the solid, and dissolving with n-hexane.
Example 4
The embodiment provides a CdSe/Cd 0→0.2 Zn 1→0.8 Se/Cd 0→0.2 Zn 1→0.8 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
(1)Cd 0→0.2 Zn 1→0.8 coating of Se layer:
in step 3), the CdSe core is uv=525nm, od=50, 25nmol;
in step 5), 0.2M Cd (OA) 2 The dropping speed is 2.5mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 Is 2X 10 4 mol/h), the dripping duration is 12min;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:30:60.
(2)Cd 0→0.2 Zn 1→0.8 coating of an S layer:
in step 5), 0.2M Cd (OA) 2 The dropping speed is 2.5mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 Is 2X 10 4 mol/h), the dripping duration is 12min;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:15:30.
example 5
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 SeS/Cd 0→0.15 Zn 1→0.85 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
(1)Cd 0→0.1 Zn 1→0.9 coating of SeS layer:
in the step 2), the Se powder is 0.5mmol, the S powder is 0.25mmol, and the Se powder is dissolved in 1mL TBP;
In step 5), 0.2M Cd (OA) 2 The dropping speed is 1.8mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 The drop velocity of (2) was 1.44X10 4 mol/h), the dropwise adding duration is 8.5min;
wherein, cd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:59:118.
(2)Cd 0→0.15 Zn 1→0.85 coating of an S layer:
in the step 2), the S powder consumption is increased to 0.5mmol and is dissolved in 1mL TBP;
in step 5), 0.2M Cd (OA) 2 The dropping speed is 1.8mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 The drop velocity of (2) was 1.44X10 4 mol/h), the dropwise adding duration is 12.5min;
wherein, stepCd (OA) used in step 1) and step 5) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:29.5:59.
example 6
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
Cd 0→0.1 Zn 1→0.9 in the coating process of Se layer, 0.2M Cd (OA) 2 The drop rates were 0.625mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 Is 5×10 3 mol/h), the duration of the dropwise addition was 30min, cd (OA) was used 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:48:96;
Cd 0→0.1 Zn 1→0.9 In the S layer coating process, 0.2M Cd (OA) 2 The drop rates were 0.625mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 Is 5×10 3 mol/h), the duration of the dropwise addition was 30min, cd (OA) was used 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:24:48.
example 7
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
Cd 0→0.1 Zn 1→0.9 in the coating process of Se layer, 0.2M Cd (OA) 2 The drop rate is 12.5mL/h (Cd (OA) under the condition of obtaining one mole of quantum dot core by the same calculation) 2 The drop velocity of (2) is 1×10 5 mol/h), cd (OA) is used 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:72:144 (144);
Cd 0→0.1 Zn 1→0.9 in the S layer coating process, 0.2M Cd (OA) 2 The dropping speed is 12.5mL/h (one mole is obtained by calculation in the same way)Cd (OA) under quantum dot nuclei 2 The drop velocity of (2) is 1×10 5 mol/h), cd (OA) is used 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and ligand solvent was 1:36:72.
example 8
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the reaction temperature in step (1) and step (2) was 250 ℃.
Example 9
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the reaction temperature in both step (1) and step (2) was 310 ℃.
Example 10
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the ligand solvent used in the step (1) and the step (2) is dodecanoic acid, cd (OA) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and dodecanoic acid was 1:1:10.
Example 11
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the ligand solvent used in step (1) and step (2) is tetradecanoic acid, cd (OA) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and fourteen is 1:200:500.
Example 12
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the ligand solvent used in step (1) and step (2) is hexadecanoic acid, cd (OA) 2 Middle Cd, zn (Ac) 2 The molar ratio between Zn and hexadecanoic acid is 1:50:20.
Example 13
The embodiment provides a CdSe/Cd 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The preparation method of the S core-shell quantum dot has the following operation steps as in example 3, and the difference from example 3 is that:
the Se powder and the S powder in the step 2) are both 0.5mmol.
Example 14
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 20s of reaction in step 5), 0.2M Cd (OA) was added dropwise at a constant rate of 1.2mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 15
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 1min of reaction in step 5), 0.2M Cd (OA) was added dropwise at a constant rate of 1.2mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 16
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 2min of reaction in step 5), 1.2mL of0.2M Cd (OA) was added dropwise at a constant rate/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 17
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 3min of reaction in step 5), 0.2M Cd (OA) was added dropwise at a constant rate of 1.2mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 18
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 5min of reaction in step 5), 0.2M Cd (OA) was added dropwise at a constant rate of 1.2mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 19
The embodiment provides a CdSe/Cd 0→0.05 Zn 1→0.95 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
after 30min of reaction in step 5), 0.2M Cd (OA) was added dropwise at a constant rate of 1.2mL/h 2 (similarly, cd (OA) under the condition of obtaining one mole of quantum dot core by calculation 2 The drop velocity of (2) was 9.6X10 3 mol/h), the duration of the dropwise addition was 6min.
Example 20
This example provides a method for fabricating a QLED device, which selects CdSe/Cd synthesized in example 3 with a wavelength of 530nm 0→0.1 Zn 1→0.9 Se/Cd 0→0.1 Zn 1→0.9 The S core-shell quantum dot is used for preparing a QLED device, and the preparation method comprises the following steps:
on a glass substrate with ITO coating, at 4000rpm, a PEDOT: PSS solution (Baytron PVPAl 4083, filtered through a 0.45mm N66 filter paper) was spin-coated for 1 minute and baked at 140℃for 10 minutes; sequentially spin-coating a chlorobenzene solution of PVK, the core-shell quantum dots and an ethanol solution of ZnO nano particles at a rotating speed of 2000rpm for 45 seconds, wherein the thickness of the core-shell quantum dot coating is about 40nm; then plating a 100nm Ag layer by using a vacuum evaporation method; finally, the device is enclosed in the organic glass by ultraviolet light curing resin.
Comparative example 1
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
cd (OA) in step 5) 2 The addition mode is that 0.2M Cd (OA) is injected at one time 2 The reaction time was 5min.
Comparative example 2
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
Cd (OA) in step 5) 2 The addition mode is that 0.2M Cd (OA) is injected at one time 2 The reaction time was 10min.
Comparative example 3
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
cd (OA) in step 5) 2 The addition mode is that 0.2M Cd (OA) is injected at one time 2 The reaction time was 30min.
Comparative example 4
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
removing step 5), adding steps between step 3) and step 4): disposable injection Cd (OA) 2 The reaction time was 5min.
Comparative example 5
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
removing step 5), adding steps between step 3) and step 4): disposable injection Cd (OA) 2 The reaction time was 10min.
Comparative example 6
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
removing step 5), adding steps between step 3) and step 4): disposable injection Cd (OA) 2 The reaction time was 20min.
Comparative example 7
This comparative example provides a CdSe/Cd 0.1 Zn 0.9 The preparation method of Se core-shell quantum dots has the following operation steps as in example 2, and the difference from example 2 is that:
removing step 5), adding steps between step 3) and step 4): disposable injection Cd (OA) 2 The reaction time was 30min.
An SEM image of CdSe core in example 1 above is shown in fig. 1; SEM images of the core-shell quantum dots in the above example 2 and the above example 19 are shown in (a) and (b) of fig. 2, respectively; the SEM images of the core-shell quantum dots in the above example 3 and the comparative example 1 are respectively shown in fig. 3 and fig. 4, and the SEM images of the core-shell quantum dots in the above comparative example 7 are respectively shown in fig. 5. Comparing the electron microscope images of fig. 1 to 3 (corresponding to example 2,3,19) and fig. 4 to 5 (corresponding to comparative examples 1 and 7), it is obvious that the particle morphology is more regular and uniform when the shell coating is performed by dripping Cd, the size morphology is controllable, and the particle morphology is obviously worse and the particle size distribution is wider when the shell coating is performed by injecting.
The core-shell quantum dots of examples 2 to 19 and examples 1 to 7 were tested for fluorescence emission peak, half-width, QY and average particle size, respectively, in examples 3 to 13 The performance of the core-shell quantum dots obtained after step (1) and step (2) was tested and the External Quantum Efficiency (EQE) and 100cd m of the QLED of example 20 were measured -2 T of brightness 50 The life was measured and the test results are shown in the following table.
Figure BDA0002213703000000151
Figure BDA0002213703000000161
As can be seen from the above test results, compared with comparative examples 1 to 7, the quantum dots of examples 1 to 19 have higher quantum efficiency (QY) and can reach 90 to 100%, and the half-peak width of the core-shell quantum dots can be stabilized below 25 nm; in addition, the QLEDs prepared by using the quantum dots in example 3 as the light-emitting layer have EQEs of 10% or more and 100cd m -2 The T50 life of the brightness is above 10,000 hours.
From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:
1. the invention takes CdSe as a core, synthesizes a shell layer by adding Cd cations at a constant speed, thereby realizing the preparation of green core-shell quantum dots under the condition of doping more Cd;
2. compared with the method for injecting Cd cations at a time, the method reduces the overlarge concentration of the local Cd cations caused by the injection at a constant speed by adding the Cd cations at a constant speed, thereby reducing the generation of CdSe small particles, ensuring the relatively narrow particle size distribution of the synthesized quantum dots in the coating process, and further maintaining the half-peak width of the quantum dots;
3. Because the reactivity of Cd cations is obviously higher than that of Zn cations, anions react preferentially to Cd in the reaction system at the same time, so that the Cd content in the shell layer is enriched near the core, and the Cd content in the outer shell layer is very low; the method can uniformly distribute the Cd content in the shell layer in the whole shell layer range by uniformly adding Cd, ensures that the Cd content of the quantum dot shell layer in the coating process is uniform and controllable, and can regulate and control the Cd content doped in each single shell layer by further controlling the adding rate and the adding time so that the thickness of the quantum dot synthesis is more controllable;
4. as each single shell layer is uniformly doped with Cd in the coating process, the valence band energy level of the quantum dot can be effectively regulated, the injection energy barrier of electrons and holes of the quantum dot during the operation of the device is reduced, the performance of the electroluminescent device with the quantum dot is further improved, experiments show that the EQE of the QLED prepared by taking the quantum dot as a light-emitting layer is more than 10 percent and 100Cd m -2 T of brightness 50 The service life is more than 10,000 hours (minimum requirement of commercial standard).
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (14)

1. The preparation method of the core-shell quantum dot is characterized by comprising the following steps of:
step S1, mixing and heating a first zinc precursor, a first VI element precursor, a first ligand and a CdSe core in a first non-coordinating solvent to obtain a first reactant system;
step S2, adding a first cadmium precursor into the first reactant system at a constant speed, and coating a cadmium-doped first Cd on the CdSe core x -Zn 1-x Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI quantum dots;
step S3, a second zinc precursor, a second VI element precursor, a second ligand and the CdSe/Cd x -Zn 1-x -mixing and heating VI quantum dots in a second non-coordinating solvent to obtain a second reactant system, wherein the second group VI element precursor is different from the first group VI element precursor;
step S4, adding the second cadmium precursor at uniform speedInto the second reactant system and in the CdSe/Cd x -Zn 1-x Cladding cadmium ion doped second Cd on-VI quantum dot y -Zn 1-y Purifying the shell of the-VI to obtain CdSe/Cd x -Zn 1-x -VI/Cd y -Zn 1-y -VI quantum dots,
wherein X is more than 0 and less than or equal to 0.1, Y is more than 0 and less than or equal to 0.1.
2. The method according to claim 1, wherein the step S1 comprises:
step S11, mixing and heating the first zinc precursor, the CdSe core, the first ligand and the first non-coordinating solvent to obtain a first mixed solution;
And step S12, adding the first VI element precursor into the first mixed solution under the heating condition to react, so as to obtain the first reactant system.
3. The method according to claim 2, wherein the reaction time in the step S12 is 20S to 5min.
4. The method according to claim 1, wherein the step S3 comprises:
step S31, the second zinc precursor, the second ligand and the CdSe/Cd are mixed x -Zn 1-x -VI quantum dots and the second non-coordinating solvent are mixed and heated to obtain a second mixed solution;
and step S32, adding the second VI element precursor into the second mixed solution under the heating condition to react, so as to obtain the second reactant system.
5. The method according to claim 4, wherein the reaction time in the step S32 is 20S to 5min.
6. The method of claim 1, wherein the first cadmium precursor and/or the first cadmium precursor is/are selected from the group consisting of a cadmium halide, and a cadmium halideThe uniform speed of the second cadmium precursor is 5 multiplied by 10 3 ～1×10 5 mol/h。
7. The method according to claim 6, wherein the uniform addition is dropwise addition, and the duration of the dropwise addition is 1min to 30min.
8. The method according to any one of claims 1 to 7, wherein the reaction temperature of step S1 to step S4 is independently selected from any one of 250 to 310 ℃.
9. The method according to any one of claims 1 to 7, wherein the molar ratio of Cd in the first cadmium precursor, zn in the first zinc precursor, free first ligand is 1:1:10-1: 200:500, wherein the molar ratio of Cd in the second cadmium precursor, zn in the second zinc precursor and the free second ligand is 1:1:10-1:200:500.
10. The production method according to any one of claims 1 to 7, wherein the first group VI element precursor is a Se precursor or a mixed precursor of Se and S, the second group VI element precursor is an S precursor, and the first zinc precursor and the second zinc precursor are the same or different.
11. The production method according to claim 10, wherein when the first group VI element precursor is a mixed precursor of Se and S, a molar ratio of the Se precursor and the S precursor is 1 or more.
12. The method of any one of claims 1 to 7, wherein the first exciton peak of the CdSe core is selected from 495 to 545nm.
13. A quantum dot composition comprising core-shell quantum dots, wherein the core-shell quantum dots are prepared by the preparation method of any one of claims 1 to 12.
14. A quantum dot light emitting device comprising core-shell quantum dots, characterized in that the core-shell quantum dots are prepared by the preparation method of any one of claims 1 to 12.
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Citations (2)

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Publication number Priority date Publication date Assignee Title
CN108251117A (en) * 2018-02-09 2018-07-06 纳晶科技股份有限公司 Core-shell quanta dots and preparation method thereof and the electroluminescent device containing it
CN108841373A (en) * 2018-05-11 2018-11-20 纳晶科技股份有限公司 A kind of red light quantum point, its synthetic method and light emitting diode with quantum dots

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN108251117A (en) * 2018-02-09 2018-07-06 纳晶科技股份有限公司 Core-shell quanta dots and preparation method thereof and the electroluminescent device containing it
CN108841373A (en) * 2018-05-11 2018-11-20 纳晶科技股份有限公司 A kind of red light quantum point, its synthetic method and light emitting diode with quantum dots

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