CN113122235A - Preparation method of quantum dots - Google Patents
Preparation method of quantum dots Download PDFInfo
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- CN113122235A CN113122235A CN201911423817.9A CN201911423817A CN113122235A CN 113122235 A CN113122235 A CN 113122235A CN 201911423817 A CN201911423817 A CN 201911423817A CN 113122235 A CN113122235 A CN 113122235A
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- B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
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Abstract
The invention provides a preparation method of quantum dots, which comprises the following steps: providing a quantum dot crystal nucleus, a shell cation precursor and a shell anion precursor; the shell layer cation precursor comprises a first shell layer cation precursor and a second shell layer cation precursor, and/or the shell layer anion precursor comprises a first shell layer anion precursor and a second shell layer anion precursor; and continuously adding a shell cation precursor and a shell anion precursor into the quantum dot crystal nucleus to form a reaction system, heating for reaction, and growing a shell on the surface of the quantum dot crystal nucleus to prepare the quantum dot.
Description
Technical Field
The invention belongs to the technical field of quantum dots, and particularly relates to a preparation method of a quantum dot.
Background
For semiconductor materials, the valence band electrons are not fixed into bonds, but are completely delocalized throughout the crystal, regardless of the state of the bulk structure or the nanoscale. When excited by external energy light, electricity, or the like, an electron transits from a ground state (valence band) to an excited state (conduction band), leaving a hole in the valence band, and at this time, a part of the electron and the hole in the excited state form a hole-electron pair, i.e., an exciton, and when the electron returns to the ground state from the excited state, the electron and the hole recombine to release energy and emerge in the form of light. But due to the high specific surface area of the quantum dots, atoms not protected by the ligand will exist in a defect state; because the electrons and the holes of the quantum dots are in a delocalized state, and the defects have the capability of capturing the electrons and the holes, some rapid non-radiative channels are introduced into the exciton recombination of the quantum dots, and the recombination rate of the non-radiative channels brought by most of the defects is far greater than that of the radiative channels, so that the luminous efficiency of the quantum dots is greatly reduced.
For solving the problem of fluorescence instability of the quantum dots, the method can be considered from the aspects of changing the ligand coating on the surface of the quantum dots and growing a wide-band gap shell layer on the surface of a quantum dot crystal nucleus. Because excitons of the quantum dots with single components are delocalized in the whole quantum dot, and ligand protection cannot reach one hundred percent, the performance influence caused by defects cannot be solved by a ligand modification method; the property of the quantum dot is improved by growing the material of the shell layer with wide band gap, and electrons and holes are confined in the nuclear material, so that the capability of resisting the environmental influence is greatly improved, mainly in a Type I structure; a core-shell structure with high confinement capacity is selected from an energy band structure, ZnS is used as the shell layer to be the best, but the synthesis difficulty is high due to the huge lattice mismatching degree, so the existing shell layer selection scheme is to grow shell layer quantum dots of an alloy structure in a gradient alloy mode, for example, shell layers CdZnS, CdZnSeS, CdSeS and the like of gradient alloy are coated on the outer layer of a quantum dot core; but with the change of different shell materials and the increase of the shell thickness in the growth process, the defect problem caused by the band gap step between the core and the shell or between the shell and the shell can also be faced.
Currently, an alternating ion-layer adsorption growth method (SILAR) (J AM Chem Soc.2003,125,12567) is used as a general method for coating a shell layer on the surface of a quantum dot crystal nucleus, but only a shell layer material with a fixed component ratio can be grown or a shell layer structure with gradually changed band gap steps can be grown through artificial adjustment.
Disclosure of Invention
The invention aims to provide a preparation method of quantum dots, and aims to solve the problem that a band gap step is generated due to lattice mismatch between a core and a shell or between the shell and the shell in the growth process of a quantum dot shell layer.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a preparation method of quantum dots, which comprises the following steps:
providing a quantum dot crystal nucleus, a shell cation precursor and a shell anion precursor; the shell layer cation precursor comprises a first shell layer cation precursor and a second shell layer cation precursor, and/or the shell layer anion precursor comprises a first shell layer anion precursor and a second shell layer anion precursor;
continuously adding a shell cation precursor and a shell anion precursor into a quantum dot crystal nucleus to form a reaction system, heating for reaction, and growing a shell on the surface of the quantum dot crystal nucleus to prepare the quantum dot, wherein,
in the step of continuously adding the shell cation precursor, adjusting the relative proportion of the first shell cation precursor and the second shell cation precursor so that the content ratio of the first shell cation precursor and the second shell cation precursor is gradually reduced along with the progress of the reaction; and/or
In the step of continuously adding the shell anion precursor, the relative proportions of the first shell anion precursor and the second shell anion precursor are adjusted so that the content ratio of the first shell anion precursor to the second shell anion precursor gradually decreases as the reaction proceeds.
According to the preparation method of the quantum dot, the concentration of two shell cations and/or two shell anions is continuously changed by controlling the reaction concentration of the two shell cations and/or the two shell anions, so that the quantum dot shell with the structure of continuously widening the band gap is grown on the outer layer of the quantum dot crystal nucleus, the crystal boundary defect is reduced, and the problem that a wide band gap protective layer is difficult to grow due to the lattice mismatching is solved. The preparation method of the quantum dot provided by the invention can also form a compact shell layer, so that the light efficiency, the anti-water-oxygen capacity and the anti-photo-oxidation capacity of the obtained quantum dot are obviously improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings needed to be used in the embodiments or the prior art descriptions will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise.
Fig. 1 is a flow chart of a preparation process of quantum dots provided by an embodiment of the invention;
FIG. 2 is a schematic diagram of an apparatus for preparing quantum dots, according to an embodiment of the present invention;
FIG. 3 is a TEM image of the alloy quantum dots prepared in example 1 of the present invention;
fig. 4 is a graph showing an absorption spectrum and an emission spectrum of the alloy quantum dot prepared in example 1 of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the description of the present invention, it is to be understood that the terms "first", "second" and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless specifically defined otherwise.
The weight of the related components mentioned in the description of the embodiments of the present invention may not only refer to the specific content of each component, but also represent the proportional relationship of the weight among the components, and therefore, the content of the related components is scaled up or down within the scope disclosed in the description of the embodiments of the present invention as long as it is in accordance with the description of the embodiments of the present invention. Specifically, the weight described in the description of the embodiment of the present invention may be a unit of mass known in the chemical industry field, such as μ g, mg, g, and kg.
As shown in fig. 1, an embodiment of the present invention provides a method for preparing a quantum dot, including the following steps:
s01, providing a quantum dot crystal nucleus, a shell cation precursor and a shell anion precursor; the shell layer cation precursor comprises a first shell layer cation precursor and a second shell layer cation precursor, and/or the shell layer anion precursor comprises a first shell layer anion precursor and a second shell layer anion precursor;
s02, continuously adding a shell cation precursor and a shell anion precursor into a quantum dot crystal nucleus to form a reaction system, heating for reaction, growing a shell on the surface of the quantum dot crystal nucleus, and preparing to obtain the quantum dot, wherein,
in the step of continuously adding the shell cation precursor, adjusting the relative proportion of the first shell cation precursor and the second shell cation precursor so that the content ratio of the first shell cation precursor and the second shell cation precursor is gradually reduced along with the progress of the reaction; and/or
In the step of continuously adding the shell anion precursor, the relative proportions of the first shell anion precursor and the second shell anion precursor are adjusted so that the content ratio of the first shell anion precursor to the second shell anion precursor gradually decreases as the reaction proceeds.
According to the preparation method of the quantum dot provided by the embodiment of the invention, the concentrations of the two shell cations and/or the two shell anions are continuously changed by controlling the reaction concentrations of the two shell cations and/or the two shell anions, so that the quantum dot shell with the structure of continuously widening the band gap is grown on the outer layer of the quantum dot crystal nucleus, the crystal boundary defect is reduced, and the problem that a wide band gap protective layer is difficult to grow due to the lattice mismatching degree is avoided. The preparation method of the quantum dot provided by the invention can also form a compact shell layer, so that the light efficiency, the anti-water-oxygen capacity and the anti-photo-oxidation capacity of the obtained quantum dot are obviously improved.
Specifically, in step S01, a quantum dot crystal nucleus of the surface shell to be grown is provided, and the selection of the quantum dot crystal nucleus is not critical and may be a quantum dot crystal nucleus conventional in the art. In some embodiments, the quantum dot nuclei are selected from binary, multiple, and multiple nuclei of group II-VI, III-V, and IV-VI elements. The quantum dot crystal nucleus can be a gradient alloy or a quantum dot with a core-shell structure. In some embodiments, the quantum dot nuclei are spherical quantum dot nuclei. When the quantum dot crystal nucleus is spherical, the control of the crystal interface activity is facilitated in the process of growing the shell layer on the surface of the quantum dot, so that the quantum dot with the core-shell structure with minimized crystal boundary defects is obtained.
A shell cation precursor and a shell anion precursor for growing the shell are provided. The shell cation precursor at least comprises a first shell cation precursor, and the shell anion precursor at least comprises a first shell anion precursor. In addition, the shell cation precursor further comprises at least a second shell cation precursor, and/or the shell anion precursor further comprises a second shell anion precursor. In some embodiments, the shell cation precursor comprises a first shell cation precursor and a second shell cation precursor, the shell anion precursor comprising a first shell anion precursor; in some embodiments, the shell cation precursor comprises a first shell cation precursor, the shell anion precursor comprises a first shell anion precursor and a second shell anion precursor; in some embodiments, the shell cation precursor comprises a first shell cation precursor and a second shell cation precursor, and the shell anion precursor comprises a first shell anion precursor and a second shell anion precursor.
The selection of the first and second shell anion precursors is not critical, and anion precursors conventionally used in the art for forming quantum dot shells may be selected, and in some embodiments, the first and second shell anion precursors are each independently selected from one of inorganic substances containing selenium or/and sulfur elements, organic phosphorus complexes, fatty amine compounds, fatty acid compounds, organic compounds, and organic alcohol compounds.
The selection of the first shell cation precursor and the second shell cation precursor is not strictly limited, and cation precursors conventionally used in the field for forming quantum dot shells can be selected, and in some embodiments, the first shell cation precursor and the second shell cation precursor are each independently selected from one of cadmium element compounds and zinc element compounds.
In the step S02, a shell cation precursor and a shell anion precursor are continuously added to the quantum dot crystal nucleus to form a reaction system, and a shell is grown on the surface of the quantum dot crystal nucleus by heating and reacting.
Because at least one of the shell cation and the shell anion comprises two ion types, in order to avoid the problem that lattice mismatch between a shell and a shell is caused in the process of generating the shell and a band gap step is generated, in the embodiment of the invention, in the process of continuously adding the shell cation and the shell anion, the addition amount of the two shell cations and/or the two shell cations is regulated and controlled, so that the concentration of the two shell cations and/or the two shell anions is continuously changed, the quantum dot shell with the continuously widened band gap structure is grown on the outer layer of the quantum dot crystal nucleus, and the defect of a crystal boundary is reduced.
Specifically, when the shell cation precursor includes a first shell cation precursor and a second shell cation precursor, in the step of continuously adding the shell cation precursor, the relative proportion of the first shell cation precursor to the second shell cation precursor is adjusted so that the content ratio of the first shell cation precursor to the second shell cation precursor gradually decreases as the reaction proceeds. Namely: in the step of continuously adding the shell cation precursor, with the total amount of the shell cation precursor to be added as 100, the content of the first shell cation precursor is gradually reduced, and the content of the second shell cation precursor is gradually increased, so that the concentration of the first shell cation precursor is unchanged, but the concentration of the second shell cation precursor is continuously increased in the shell cation precursor participating in the reaction.
In some embodiments, the molar content of the second shell cation precursor increases at a rate of 1% to 50%/h, based on 100 total moles of the shell cation precursor to be added. In some embodiments, the molar content increase rate of the second shell cation precursor is 1%/h, 5%/h, 10%/h, 15%/h, 20%/h, 25%/h, 30%/h, 35%/h, 40%/h, 45%/h, 50%/h, based on the total molar amount of the shell cation precursors to be added being 100.
When the shell-layer anion precursor includes a first shell-layer anion precursor and a second shell-layer anion precursor, in the step of continuously adding the shell-layer anion precursor, the relative ratio of the first shell-layer anion precursor to the second shell-layer anion precursor is adjusted so that the content ratio of the first shell-layer anion precursor to the second shell-layer anion precursor gradually decreases as the reaction proceeds. Namely: in the step of continuously adding the shell anion precursor, with the total amount of the shell anion precursor to be added as 100, the content of the first shell anion precursor is gradually reduced, and the content of the second shell anion precursor is gradually increased, so that the concentration of the first shell anion precursor is unchanged, but the concentration of the second shell anion precursor is continuously increased in the shell cation precursor participating in the reaction.
In some embodiments, the molar content of the second shell anion precursor increases at a rate of 1% to 50%/h, based on 100 total moles of the shell anion precursor to be added. In some embodiments, the molar content of the second shell anion precursor increases by 1%/h, 5%/h, 10%/h, 15%/h, 20%/h, 25%/h, 30%/h, 35%/h, 40%/h, 45%/h, 50%/h, based on 100 total molar amount of the shell anion precursor to be added.
When the shell cation precursor comprises a first shell cation precursor and a second shell cation precursor, and when the shell anion precursor comprises a first shell anion precursor and a second shell anion precursor, adjusting the relative proportion of the first shell cation precursor and the second shell cation precursor, so that the content ratio of the first shell cation precursor and the second shell cation precursor is gradually reduced along with the reaction; in the step of continuously adding the shell anion precursor, the relative proportions of the first shell anion precursor and the second shell anion precursor are adjusted so that the content ratio of the first shell anion precursor to the second shell anion precursor gradually decreases as the reaction proceeds. Namely: in the step of continuously adding the shell cation precursor, with the total amount of the shell cation precursor to be added as 100, the content of the first shell cation precursor is gradually reduced, and the content of the second shell cation precursor is gradually increased, so that the concentration of the first shell cation precursor is unchanged, but the concentration of the second shell cation precursor is continuously increased in the shell cation precursor participating in the reaction; meanwhile, in the step of continuously adding the shell anion precursor, with the total amount of the shell anion precursor to be added as 100, the content of the first shell anion precursor is gradually reduced, and the content of the second shell anion precursor is gradually increased, so that the concentration of the first shell anion precursor is unchanged, but the concentration of the second shell anion precursor is continuously increased in the shell cation precursor participating in the reaction.
In some embodiments, the molar content of the second shell cation precursor increases by 1% to 50%/h, based on 100 total moles of the shell cation precursor to be added; and the molar content acceleration rate of the anion precursor of the second shell layer is 1-50%/h, wherein the total molar weight of the anion precursor of the shell layer to be added is 100. In some embodiments, the molar content increase rate of the second shell cation precursor is 25%/h, based on the total molar amount of the shell cation precursors to be added being 100; and the molar content acceleration rate of the second shell layer anion precursor is 25%/h, wherein the total molar weight of the shell layer anion precursor to be added is 100.
In the embodiment of the invention, the selection of the first shell cation precursor and the second shell cation precursor can be randomly selected from different shell cation precursors. In some embodiments, the first shell cation precursor and the second shell cation precursor satisfy: the band gap of the shell layer formed by the first shell layer cation precursor and the anion precursor is smaller than the band gap of the shell layer formed by the second shell layer cation precursor and the same anion precursor. The band gap of the shell layer obtained by the method is gradually increased, the quantum dot shell layer with the continuously widened band gap structure can grow on the outer layer of the quantum dot crystal nucleus by controlling the continuous change of the concentration of the precursor, and the defect of a crystal boundary is reduced, so that the problem that a wide band gap protective layer is difficult to grow due to the lattice mismatching degree is solved. In some embodiments, the first shell cation precursor is selected from a cadmium source and the second shell cation is selected from a zinc source.
In the embodiment of the invention, the selection of the first shell layer anion precursor and the second shell layer anion precursor can be randomly selected from different shell layer anion precursors. In some embodiments, the first shell anion precursor and the second shell anion precursor satisfy: the band gap of the shell layer formed by the first shell layer anion precursor and the cation precursor is smaller than the band gap of the shell layer formed by the second shell layer anion precursor and the same cation precursor. The band gap of the obtained shell layer is gradually increased, and the quantum dot shell layer with the continuously widened band gap structure can grow on the outer layer of the quantum dot crystal nucleus by controlling the continuous change of the concentration of the precursor, so that the defect of a crystal boundary is reduced, and the problem that a wide band gap protective layer is difficult to grow due to the lattice mismatching degree is avoided; in some embodiments, the first shell anion and/or the second shell anion is selected from at least one of selenium or/and sulfur-containing inorganic substances, organic phosphorus complexes, fatty amine compounds, fatty acid compounds, organic compounds, and organic alcohol compounds.
In some embodiments, the first shell cation precursor and the second shell cation precursor satisfy: the band gap of a shell layer formed by the first shell layer cation precursor and the anion precursor is smaller than the band gap of a shell layer formed by the second shell layer cation precursor and the same anion precursor; and the first shell layer anion precursor and the second shell layer anion precursor satisfy: the band gap of the shell layer formed by the first shell layer anion precursor and the cation precursor is smaller than the band gap of the shell layer formed by the second shell layer anion precursor and the same cation precursor.
In the examples of the present invention, the amounts of the shell cation precursor and the shell anion to be added were calculated, and in some examples, the amounts of the shell cation precursor and the shell anion to be added were determined by quantifying crystal nuclei according to an extinction coefficient measurement method reported in the literature (Chem mater.2003,15,2854). On this basis, it is preferable that the sum of the products of the molar amount and the valence of the shell cation precursor is larger than the sum of the products of the molar amount and the valence of the shell anion precursor. Thereby, the content of the cationic precursor can be made higher than that of the anionic precursor. Because the surface ligand of the quantum dot is in an anion type and forms a bond with the quantum dot through cation coordination, the stability and the photoelectric property of the quantum dot are improved when the surface of the quantum dot is rich in cations.
On the basis of the above embodiment, the reaction system further comprises a coordination solvent and a non-coordination solvent. The coordination solvent is used for providing a surface ligand for the prepared core-shell quantum dot; the non-coordinating solvent serves as a dissolving and dispersing solvent and also as a reaction medium.
In some embodiments, the coordinating solvent is selected from at least one of saturated or unsaturated fatty acids having 6 or more carbon atoms. In this case, the formed ligand chain has a relatively long length, and can improve the dispersibility of the quantum dots and prevent the agglomeration of the quantum dots.
In some embodiments, the non-coordinating solvent is at least one selected from the group consisting of alkanes having 10 to 22 carbon atoms, alkenes, ethers, and aromatics. In this case, the boiling point of the solvent is high, and the upper limit of the reaction temperature is increased, thereby reducing the limitation of the reaction temperature on the selection of the crystal nucleus or shell material.
It should be understood that, in the step of continuously adding the shell cation precursor and the shell anion precursor to form the reaction system in the quantum dot crystal nucleus, the shell cation precursor and the shell anion precursor may be continuously added to the quantum dot crystal nucleus solution to form the reaction system, or the shell cation precursor solution and the shell anion precursor solution may be continuously added to the quantum dot crystal nucleus solution to form the reaction system. At this time, the quantum dot crystal nucleus solution comprises quantum dot crystal nuclei, a ligand solvent and/or a non-coordinating solvent; the shell layer cation precursor solution comprises a shell layer cation precursor, a ligand solvent and/or a non-coordination solvent; the shell layer anion precursor solution comprises a shell layer anion precursor, a ligand solvent and/or a non-coordinating solvent.
In some embodiments, the shell cation precursor solution comprises a first metal source or/and a second metal source, a ligand solvent, and a non-coordinating solvent; in some embodiments, the shell anion precursor solution comprises elemental or compound of tellurium, selenium, elemental sulfur, a coordinating solvent, or/and a non-coordinating solvent.
On the basis of the above examples, the reaction system was subjected to heat treatment to grow a shell layer having a continuously widened band gap on the surface of the quantum dot crystal nucleus. In some embodiments, the temperature of the heating reaction is 260 ℃ or less. In this case, the shell layer cation and anion can orderly react and be combined on the surface of the quantum dot crystal nucleus. If the temperature of the heating reaction is too high, the activity of anions and cations of the shell is too high, and the anions and the cations form nuclei independently, so that the growth of the shell is not facilitated.
In a particularly preferred embodiment, as shown in fig. 2, a shell cation precursor and a shell anion precursor are continuously added to a quantum dot crystal nucleus to form a reaction system, and the reaction is heated to grow a shell on the surface of the quantum dot crystal nucleus in a reaction device; the reaction device comprises a reactor at least provided with a first opening and a second opening, a first shell layer cation precursor liquid storage container communicated with the first opening, a first anion precursor liquid storage container identical to the second opening, a second shell layer cation precursor liquid storage container communicated with the first shell layer cation precursor liquid storage container and/or a second anion precursor liquid storage container communicated with the first anion precursor liquid storage container. In this case, the continuous addition of the respective solutions can be effected by means of syringe pumps.
In some embodiments, a second cation (anion) precursor is continuously added into a liquid storage container of a first cation (anion) precursor by a syringe pump to be uniformly mixed, the component content of the second cation (anion) precursor in the liquid storage container of the first cation (anion) precursor is linearly increased, and simultaneously, the uniformly mixed cation precursor and anion precursor are simultaneously dripped into a reaction device containing quantum dot crystal nuclei to grow a gradient shell layer. Under the condition, the total amount of the cation (anion) precursor mixing process can be effectively controlled, and the gradient change of the cation and the anion can be adjusted, so that the gradient shell with continuously gradient-changed shell components can be obtained. Therefore, the quantum dot shell material with the structure of minimizing crystal boundary defects and continuously widening band gaps can grow on the outer layer of the quantum dot crystal nucleus, the problem that a wide band gap protective layer is difficult to grow due to the fact that the degree of lattice mismatching is avoided, a compact shell can be formed, and the luminous efficiency, the anti-water-oxygen capacity and the anti-photooxidation capacity of the quantum dot material are improved obviously.
In some embodiments, the first shell cation precursor is placed in a first shell cation precursor reservoir, the second shell cation precursor is placed in a second shell cation precursor reservoir, the first shell cation precursor is continuously added to the reactor containing the quantum dot nuclei, and the second shell cation precursor is continuously added to the first shell cation precursor reservoir.
In some embodiments, the first shell anion precursor is placed in a first anion precursor reservoir, the second shell anion precursor is placed in a second anion precursor reservoir, the first anion precursor is continuously added to the reactor containing the quantum dot nuclei, and the second anion precursor is continuously added to the first shell cation precursor reservoir.
In some embodiments, the first shell cation precursor is placed in a first shell cation precursor reservoir, the second shell cation precursor is placed in a second shell cation precursor reservoir, the first shell anion precursor is placed in a first anion precursor reservoir, the second shell anion precursor is placed in a second anion precursor reservoir, the first shell cation precursor and the first anion precursor are continuously added to the reactor containing the quantum dot nuclei, the second shell cation precursor is continuously added to the first shell cation precursor reservoir, and the second anion precursor is continuously added to the first shell cation precursor reservoir.
In the embodiment of the invention, the shell structure with proper thickness can be obtained by controlling the addition amount of the anion precursor and the cation precursor of the shell. In some embodiments, the quantum dot crystal nuclei have a size of 2nm to 10nm, and the shell layer has a thickness of 1nm to 8 nm.
The method can be used for preparing the core-shell structure quantum dot with the emission peak wavelength range of 450nm-650nm, the quantum efficiency of more than 85%, the half-peak width of less than 25nm and the spherical quantum dot particle size of 6-18 nm.
The following description will be given with reference to specific examples.
Example 1
CdSe/CdxZn1-xThe preparation method of S comprises the following steps:
1mmol of cadmium oxide, 1ml of oleic acid and 9ml of octadecene were weighed out to prepare 0.1M cadmium oleate [ Cd (OA)2]A cationic precursor solution; weighing 2mmol of cadmium oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
2ml of cadmium oleate with the concentration of 0.1M is taken and placed in a first cation liquid storage container; 4ml of 0.1M zinc oleate is taken and placed in a second cation liquid storage container; 3ml of 0.2M S/TOP was placed in an anionic reservoir;
take 5X 10-2Dispersing mmol CdSe nanocrystal core in homogeneous solution of 1ml oleic acid and 5ml octadecene, vacuumizing, heating to 100 deg.C, introducing argon, and heating to 240 deg.C after water and oxygen are completely treated; when the temperature is stable, adding the cation and anion precursor solution into the reaction system at a preset speed to grow CdxZn1-xS, a gradient shell layer;
after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, precipitating and purifying the quantum dots for three times to obtain CdSe/CdxZn1-xAnd (4) S quantum dots.
CdSe/Cd prepared in embodiment 1 of the inventionxZn1-xThe TEM image of S is shown in FIG. 3, from which it can be seen: example 1 preparation of CdSe/CdxZn1-xThe S particle size is about 12nm, and the appearance is uniform.
CdSe/Cd prepared in embodiment 1 of the inventionxZn1-xThe absorption spectrum and the emission spectrum of S are shown in FIG. 4, and it can be seen from the figure that: PL 621nm, FWHM 23nm, quantum dot has better particle size uniformity.
Comparative example 1
A preparation method of CdSe/CdSnS comprises the following steps:
1mmol of cadmium oxide, 1ml of oleic acid and 9ml of octadecene were weighed out to prepare 0.1M cadmium oleate [ Cd (OA)2]A cationic precursor solution; weighing 2mmol of cadmium oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
take 3X 10-2Dispersing mmol CdSe nanocrystal core in homogeneous solution of 1ml oleic acid and 5ml octadecene, vacuumizing, heating to 100 deg.C, introducing argon, and heating to 240 deg.C after water and oxygen are completely treated; adding the cation and anion precursor solution into the reaction system when the temperature is stable,growing a CdZnS shell layer;
and after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, and precipitating and purifying the quantum dots for three times to obtain the CdSe/CdSnS quantum dots.
The CdSe/CdZnS quantum dots prepared in comparative example 1 of the present invention have PL of 628nm, FWHM of 29nm and particle size of about 10 nm.
Example 2
CdZnSe/CdxZn1-xSeyS1-yThe preparation method comprises the following steps:
1mmol of cadmium oxide, 1ml of oleic acid and 9ml of octadecene were weighed out to prepare 0.1M cadmium oleate [ Cd (OA)2]A cationic precursor solution; weighing 2mmol of cadmium oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of selenium simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
3ml of cadmium oleate with the concentration of 0.1M is taken and placed in a first cation liquid storage container; 3ml of 0.1M zinc oleate is taken and placed in a second cation liquid storage container; 1.5ml of 0.2M Se/TOP was taken and placed in a first anionic reservoir; taking 1.5ml of 0.2M S/TOP and placing the solution in a second anion liquid storage container;
will be 9X 10-2Dispersing the mmolCdZnSe nanocrystal cores in a homogeneous solution of 1ml of oleic acid and 5ml of octadecene, vacuumizing, heating to 100 ℃, introducing argon, and heating to 260 ℃ after complete water-oxygen treatment; when the temperature is stable, adding the cation and anion precursor solution into the reaction system at a preset speed to grow CdxZn1-xSeyS1-yA gradient shell layer;
after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, precipitating and purifying the quantum dots for three times to obtain CdSe/CdxZn1-xSeyS1-yAnd (4) quantum dots.
CdSe/Cd prepared in embodiment 2 of the inventionxZn1-xSeyS1-yQuantum dots, PL 634nm, FWHM 23nm, and the particle size is about 15 nm.
Comparative example 2
A preparation method of CdSe/CdZnSeS comprises the following steps:
1mmol of cadmium oxide, 1ml of oleic acid and 9ml of octadecene were weighed out to prepare 0.1M cadmium oleate [ Cd (OA)2]A cationic precursor solution; weighing 2mmol of cadmium oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of selenium simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
will be 1 × 10-1Dispersing the mmolCdZnSe nanocrystal cores in a homogeneous solution of 1ml of oleic acid and 5ml of octadecene, vacuumizing, heating to 100 ℃, introducing argon, and heating to 260 ℃ after complete water-oxygen treatment; when the temperature is stable, respectively adding a cadmium cation precursor, a zinc cation precursor, a selenium anion precursor and a sulfur anion precursor solution into a reaction system at a preset speed to grow a CdZnSeS gradient shell layer;
and after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, and precipitating and purifying the quantum dots for three times to obtain the CdSe/CdZnSeS quantum dots.
The CdSe/CdZnSeS quantum dots prepared by the comparative example 2 of the invention have the PL of 640nm, the FWHM of 36nm and the particle size of about 16 nm.
Example 3
CdSe/ZnSexS1-xThe preparation method comprises the following steps:
weighing 2mmol of zinc oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of selenium simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
2ml of cadmium oleate with the concentration of 0.1M is taken and placed in a first cation liquid storage container; 4ml of 0.1M zinc oleate is taken and placed in a second cation liquid storage container; 3ml of 0.2M S/TOP was placed in a first anionic reservoir;
take 3X 10-2Dispersing the mmolCdSe nanocrystal cores in a homogeneous solution of 1ml of oleic acid and 5ml of octadecene, vacuumizing, heating to 100 ℃, introducing argon, and heating to 250 ℃ after complete water-oxygen treatment; adding the cation and anion precursor solution into the reaction system at a constant speed when the temperature is stable, and growing ZnSexS1-xA gradient shell layer;
after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, precipitating and purifying the quantum dots for three times to obtain CdSe/ZnSexS1-xAnd (4) quantum dots.
CdSe/ZnSe prepared in embodiment 3 of the inventionxS1-xQuantum dots, PL 533nm, FWHM 22nm, with a particle size of about 9 nm.
Comparative example 3
A preparation method of CdSe/ZnSe comprises the following steps:
weighing 2mmol of zinc oxide, 2ml of oleic acid and 18ml of octadecene, 0.1M zinc oleate [ Zn (OA) ]was prepared2]A cationic precursor solution; weighing 2mmol of selenium simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution; weighing 2mmol of sulfur simple substance and 10ml of TOP, and mixing to prepare 0.2M S/TOP anion precursor solution;
take 4.5X 10-2Dispersing the mmolCdSe nanocrystal cores in a homogeneous solution of 1ml of oleic acid and 5ml of octadecene, vacuumizing, heating to 100 ℃, introducing argon, and heating to 250 ℃ after complete water-oxygen treatment; adding the zinc cation and selenium and sulfur anion precursor solution into a reaction system at a constant speed when the temperature is stable, and growing a ZnSeS shell layer;
and after the reaction is finished, cooling to room temperature, taking n-heptane as a solvent and ethanol as a non-solvent, and precipitating and purifying the quantum dots for three times to obtain the CdSe/ZnSeS quantum dots.
The CdSe/ZnSeS quantum dots prepared in comparative example 3 of the present invention had PL & lt540 nm, FWHM & lt30 nm, and particle size of about 7 nm.
The quantum dots prepared in the above examples 1 to 3 and comparative examples 1 to 3 were applied to a quantum dot light emitting diode, and the manufacturing method of the quantum dot light emitting diode was as follows:
substrate cleaning: rubbing and washing the ITO substrate glass with isopropanol and acetone, washing with a detergent if necessary, then sequentially ultrasonically washing with acetone, deionized water and absolute ethyl alcohol for 15min, then rapidly drying with a nitrogen gun, and finally treating for 10min under air plasma.
And (3) spin-coating PEDOT (PSS) on the ITO substrate at the rotating speed of 4000rpm for 40 s. After completion of the spin coating, the hole injection layer was prepared by annealing at 150 ℃ for 15min in air, and then transferred to a glove box filled with nitrogen.
Spin-coating a 10mg/mLTFB chlorobenzene solution on glass/ITO/PEDOT: PSS at a rotating speed of 2000rpm for 35s, and annealing in a glove box at 140-160 ℃ for 30min after the spin-coating is finished to prepare a hole transport layer.
The quantum dots dissolved in the n-octane solution were spin coated on the hole transport layer at 2000rpm for 50 s. The concentration of the blue light quantum dots is 15-30mg/mL, annealing is carried out for 10min at 100 ℃, and the quantum dot light-emitting layer is prepared. Wherein the quantum dots are the quantum dots prepared in examples 1-3 and comparative examples 1-3, respectively.
An ethanol solution of ZnO was spin-coated on the quantum dot layer at 2000rpm for 30 s. The concentration of ZnO was 25 mg/mL. After the spin coating was completed, annealing was performed in a glove box at 80 ℃ for 15min to prepare an electron transport layer.
And putting the sample subjected to spin coating into a vacuum cavity, and evaporating a top electrode Al, wherein the thickness of the electrode is 80 nm.
And packaging with curing glue after evaporation, and isolating water and oxygen.
Testing the quantum dots prepared in the above examples 1 to 3 and comparative examples 1 to 3 were used as the quantum dot light emitting layer materials, respectively, and the quantum dot light emitting diodes prepared according to the above methods were subjected to performance testing.
Wherein eqe (external Quantum efficiency) represents external Quantum efficiency; diameter represents the particle Diameter; QY (quantum yield) denotes the quantum yield; fwhm (full width at half maximum) denotes the half-width; pl (photoluminescence) photoluminescence; el (electroluminescence) electroluminescence.
The test results are shown in table 1 below.
TABLE 1
| PL(nm) | FWHM(nm) | QY(％) | Diameter(nm) | EQE(％) | |
| Example 1 | 621 | 23 | 90 | 12 | 18.5 |
| Example 2 | 634 | 23 | 88 | 15 | 15 |
| Example 3 | 533 | 22 | 95 | 9 | 17.3 |
| Comparative example 1 | 628 | 29 | 75 | 10 | 5.5 |
| Comparative example 2 | 640 | 36 | 78 | 16 | 3.3 |
| Comparative example 3 | 540 | 30 | 80 | 7 | 6 |
As can be seen from the above table, the quantum dot light emitting diode prepared by using the quantum dots prepared in examples 1 to 3 as the quantum dot light emitting layer material has better photoelectric properties, and the EQE of the quantum dot light emitting diode is greatly improved compared with that of comparative examples 1 to 3, which is directly related to the quantum dot shell layer of the quantum dot crystal nucleus outer layer growth band gap continuous widening structure in the examples, so that the light efficiency, the anti-aqueous oxygen capacity and the anti-photooxidation capacity of the synthesized quantum dot are obviously improved compared with that of comparative examples 1 to 3.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (10)
1. The preparation method of the quantum dot is characterized by comprising the following steps:
providing a quantum dot crystal nucleus, a shell cation precursor and a shell anion precursor; the shell cation precursor comprises a first shell cation precursor, and the shell anion precursor comprises a first shell anion precursor; the shell layer cation precursor further comprises a second shell layer cation precursor and/or the shell layer anion precursor further comprises a second shell layer anion precursor;
continuously adding a shell cation precursor and a shell anion precursor into a quantum dot crystal nucleus to form a reaction system, heating for reaction, and growing a shell on the surface of the quantum dot crystal nucleus to prepare the quantum dot, wherein,
in the step of continuously adding the shell cation precursor, adjusting the relative proportion of the first shell cation precursor and the second shell cation precursor so that the content ratio of the first shell cation precursor and the second shell cation precursor is gradually reduced along with the progress of the reaction; and/or
In the step of continuously adding the shell anion precursor, the relative proportions of the first shell anion precursor and the second shell anion precursor are adjusted so that the content ratio of the first shell anion precursor to the second shell anion precursor gradually decreases as the reaction proceeds.
2. The method for preparing a quantum dot according to claim 1, wherein the first shell cation precursor and the second shell cation precursor satisfy: the band gap of a shell layer formed by the first shell layer cation precursor and the anion precursor is smaller than the band gap of a shell layer formed by the second shell layer cation precursor and the same anion precursor; and/or
The first shell layer anion precursor and the second shell layer anion precursor satisfy the following conditions: the band gap of the shell layer formed by the first shell layer anion precursor and the cation precursor is smaller than the band gap of the shell layer formed by the second shell layer anion precursor and the same cation precursor.
3. The method of claim 1, wherein the temperature of the heating reaction is 260 ℃ or less.
4. The method of preparing a quantum dot according to claim 1, wherein the molar content of the second shell cation precursor is increased by 1% to 50%/h, based on 100 total molar amount of the shell cation precursor to be added; and/or
And the molar content acceleration rate of the anion precursor of the second shell layer is 1-50%/h, wherein the total molar amount of the anion precursor of the shell layer to be added is 100.
5. The method of any one of claims 1 to 4, wherein the reaction system further comprises a coordinating solvent and a non-coordinating solvent.
6. The method for preparing a quantum dot according to claim 5, wherein the coordinating solvent is at least one selected from saturated or unsaturated fatty acids having 6 or more carbon atoms.
7. The method according to claim 5, wherein the non-coordinating solvent is at least one selected from the group consisting of alkanes having 10 to 22 carbon atoms, alkenes, ethers, and aromatics.
8. The method of any one of claims 1 to 4, 6 and 7, wherein the sum of products of molar quantity and valence of the shell cation precursor is greater than the sum of products of molar quantity and valence of the shell anion precursor.
9. The method of any one of claims 1 to 4, 6 or 7, wherein the first shell cation precursor is selected from a cadmium source and the second shell cation is selected from a zinc source; and/or
The first shell anion and/or the second shell anion is/are selected from at least one of inorganic substances containing selenium or/and sulfur elements, organic phosphorus complexes, fatty amine compounds, fatty acid compounds, organic compounds and organic alcohol compounds.
10. The method of any one of claims 1 to 4, 6 and 7, wherein the step of continuously adding a shell cation precursor and a shell anion precursor to the quantum dot crystal nucleus to form a reaction system, heating the reaction system to grow the shell on the surface of the quantum dot crystal nucleus is performed in a reaction apparatus; the reaction device comprises a reactor at least provided with a first opening and a second opening, a first shell layer cation precursor liquid storage container communicated with the first opening, a first anion precursor liquid storage container identical to the second opening, a second shell layer cation precursor liquid storage container communicated with the first shell layer cation precursor liquid storage container and/or a second anion precursor liquid storage container communicated with the first anion precursor liquid storage container.
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