WO2022143435A1

WO2022143435A1 - Quantum dot screening method and quantum dot light-emitting diode

Info

Publication number: WO2022143435A1
Application number: PCT/CN2021/141020
Authority: WO
Inventors: 周礼宽; 杨一行
Original assignee: Tcl科技集团股份有限公司
Priority date: 2020-12-30
Filing date: 2021-12-24
Publication date: 2022-07-07
Also published as: CN114686232A; CN114686232B

Abstract

Disclosed in the present disclosure are a quantum dot screening method and a quantum dot light-emitting diode. The screening method comprises the following steps: dispersing initial quantum dots with the surfaces connected to an organic ligand in a first solvent to obtain an initial quantum dot solution; and gradually adding a non-soluble solvent into the initial quantum dot solution and mixing, gradually precipitating the initial quantum dots according to the descending order of the particle size, and sequentially collecting the precipitates according to a time order in stages so as to obtain screened quantum dots, wherein the non-soluble solvent is miscible with the first solvent, and is not miscible with the organic ligand. The minimum size deviation of the quantum dots obtained by means of separation in the present disclosure can be controlled within 5%, thereby obtaining a quantum dot material with uniform size; and using the quantum dots with uniform size as a quantum dot light-emitting layer material can effectively improve the photoelectric properties of a quantum dot light-emitting diode.

Description

A kind of sieving method of quantum dot and quantum dot light-emitting diode

priority

The present disclosure claims the priority of the Chinese patent application with the application date of December 30, 2020 and the application number of "202011617614.6" and the application title of "A method for sieving of quantum dots and quantum dot light-emitting diodes" , the entire contents of which are incorporated by reference in this disclosure.

technical field

The present disclosure relates to the field of quantum dot preparation, and in particular, to a quantum dot screening method and a quantum dot light-emitting diode.

Background technique

Quantum dots are a low-dimensional nano-semiconductor material. By applying a certain electric field or light pressure to the nano-semiconductor material, they will emit light of a specific wavelength, and the wavelength of the emitted light will vary with the size of the semiconductor. change to change. In recent years, quantum dots have attracted extensive attention from researchers at home and abroad due to their narrow emission half-peak width, high color purity, wide spectral coverage, high luminous efficiency, and good stability. Quantum dots are generally spherical or spherical-like semiconductor nanocrystals with diameters between 2 and 20 nm. Due to the small particle size, large specific surface area and strong surface activity of quantum dots, agglomeration between quantum dots is prone to occur. Therefore, when synthesizing quantum dots, the problem of particle agglomeration is avoided by connecting organic ligands on the surface of quantum dots. At the same time, it is necessary to ensure that the quantum dots can be dispersed in a specific solvent. The quantum dots can be stable without agglomeration because the repulsive force provided by the encapsulation layer formed by the organic ligands is equivalent to the van der Waals force between them, and the encapsulation layer and the solvent provide a potential barrier to prevent the agglomeration between the quantum dots.

The preparation of quantum dots is divided into two processes: nucleation and growth, mainly through the adjustment of reaction time and temperature to obtain the desired size of quantum dot particles. The resulting particle size deviation is about 20%, which is the half-peak of the quantum dot emission spectrum. In addition, in quantum dot light-emitting diode devices, the large particle size deviation of quantum dots leads to poor film flatness of the light-emitting layer, increased leakage current of the device, and may cause short-circuit problems in the functional layer.

Therefore, the existing technology still needs to be improved and developed.

SUMMARY OF THE INVENTION

In view of the above-mentioned deficiencies of the prior art, the purpose of the present disclosure is to provide a method for sieving quantum dots, which aims to solve the problem that the particle size deviation of the quantum dots prepared in the prior art is large, which causes the quality of the film formation of the light-emitting layer of the quantum dot light-emitting diode device. poor, resulting in poor optoelectronic properties.

The technical solutions of the present disclosure are as follows:

A method for sieving quantum dots, comprising the steps of:

Dispersing the initial quantum dots with organic ligands connected on the surface in the first solvent to obtain the initial quantum dot solution;

Gradually adding an insoluble solvent to the initial quantum dot solution and mixing, so that the initial quantum dots are gradually precipitated according to the order of particle size from large to small, and the precipitates are collected in sections in chronological order to obtain the sieved quantum dots, The insoluble solvent is miscible with the first solvent and immiscible with the organic ligand.

A quantum dot light-emitting diode, comprising a cathode, an anode, and a quantum dot light-emitting layer disposed between the cathode and the anode, and the quantum dot light-emitting layer material is the sieved quantum dots described in the present disclosure.

Beneficial effect: the present disclosure gradually adds an insoluble solvent that is mutually soluble with the first solvent but immiscible with the organic ligand into the initial quantum dot solution, and in a state of constant stirring, when the insoluble solvent is added dropwise to a certain amount , the initial quantum dot solution begins to flocculate, continue to stir to make the large particles completely precipitate, and then separate them by centrifugation, and then continue to add the insoluble solvent dropwise to the supernatant, repeat this several times, and collect the particles in sections The size deviation of the separated quantum dots can be controlled within 5%, so as to obtain uniform size quantum dot materials; using the uniform size quantum dots as the quantum dot light-emitting layer material can effectively Improve the optoelectronic properties of quantum dot light-emitting diodes.

Description of drawings

FIG. 1 is a flow chart of a preferred embodiment of a method for sieving quantum dots provided by the present disclosure.

FIG. 2 is a schematic structural diagram of a quantum dot light-emitting diode provided by the present disclosure.

FIG. 3 is a scanning electron microscope photograph of the original sample in Example 1 provided by the present disclosure.

FIG. 4 is a scanning electron microscope photograph of the sample of the front section in Example 1 provided by the present disclosure.

FIG. 5 is a scanning electron microscope photograph of the middle-section sample in Example 1 provided by the present disclosure.

FIG. 6 is a scanning electron microscope photograph of the back-end sample in Example 1 provided by the present disclosure.

FIG. 7 is a fluorescence emission spectrum diagram of the original sample of Example 1 and the quantum dots after sieving provided by the present disclosure.

Detailed ways

The present disclosure provides a method for sieving quantum dots and a quantum dot light-emitting diode. In order to make the purpose, technical solutions and effects of the present disclosure clearer and clearer, the present disclosure will be described in further detail below. It should be understood that the specific embodiments described herein are only used to explain the present disclosure, but not to limit the present disclosure.

The synthesis and preparation of quantum dots is divided into two processes: nucleation and growth. By controlling the reaction time, reaction temperature and composition ratio, quantum dot particles of different wavelengths can be obtained; The difference in activity, as the size of the quantum dot particles grows, the size deviation of each quantum dot particle is about 20%, which is directly manifested as the increase of the half-peak width of the quantum dot emission spectrum. The size difference of quantum dot particles becomes larger, and the surface roughness of the solid-state film of the light-emitting layer of the quantum dot light-emitting diode device prepared by using such quantum dot materials increases, which will lead to an increase in the leakage current of the device and the problem of short-circuit device failure in the functional layer. .

Based on this, the present disclosure provides a method for sieving quantum dots, as shown in FIG. 1 , which includes the steps:

S10, dispersing the initial quantum dots with organic ligands connected to the surface in the first solvent to obtain an initial quantum dot solution;

S20, gradually adding an insoluble solvent to the initial quantum dot solution and mixing, so that the initial quantum dots are gradually precipitated according to the particle size from large to small, and the precipitates are collected in chronological order to obtain the sieved quantum dots At this point, the insoluble solvent is mutually miscible with the first solvent, and is immiscible with the organic ligand.

Specifically, in the research on the preparation and application of quantum dot materials, it was found that the initial quantum dots synthesized were mainly composed of inorganic nanoparticles and an organic coating layer (organic ligand) connected to the surface of the inorganic nanoparticles through coordination bonds. Composition, the initial quantum dots can be stably dispersed in the first solvent without agglomeration and sedimentation due to the mutual repulsive force provided by the surface-coated organic ligands and the van der Waals force between the organic ligands. and the first solvent is equivalent to setting a potential barrier between the initial quantum dots to prevent the quantum dots from agglomerating and settling. When an insoluble solvent that is miscible with the first solvent for dispersing the quantum dots but immiscible with the organic ligand is introduced into the concentrated initial quantum dot solution, as the amount of the insoluble solvent in the initial quantum dot solution gradually increases, the solution The solubility of the organic coating layer decreases, that is, the mutual repulsive force that the organic coating layer can provide is weakened, and the van der Waals force therebetween is unbalanced. Since the larger size quantum dot particles have smaller specific surface area, that is, the surface energy is smaller, the potential barrier effect provided by the organic coating layer and the first solvent to the large size quantum dots is weakened most obviously, making the particles larger The quantum dots aggregate and settle first, and then the quantum dots with smaller particles aggregate and settle.

That is to say, the organic coating layer on the surface of the initial quantum dots is the key factor for the quantum dots to be dispersed in the first solvent. Based on the above analysis, in this embodiment, the initial quantum dot solution is gradually added to the initial quantum dot solution. The insoluble solvent that is immiscible with the organic ligand, in the state of constant stirring, when the insoluble solvent is added dropwise to a certain amount, the initial quantum dot solution begins to flocculate, and the stirring is continued to completely precipitate the large particles, Then it is separated by centrifugation, and the supernatant is continuously added dropwise to the insoluble solvent. This is repeated several times, and the precipitates with similar particle sizes are collected in sections. The size deviation of the isolated quantum dots can be controlled at a minimum. within 5%, so as to obtain quantum dot materials with uniform size; using the quantum dots with uniform size as quantum dot light-emitting layer material can effectively reduce the roughness of the quantum dot light-emitting layer and increase its film formation flatness, thereby effectively improving the quantum dots. Photoelectric properties of point light-emitting diodes.

In some embodiments, the precipitation is collected in sections in chronological order, and the step of obtaining the sieved quantum dots includes:

The precipitation is collected in sections according to time sequence, so that the sieved quantum dots collected in the previous stage account for 25-35% of the weight of the initial quantum dots, and are recorded as large-particle quantum dots in the previous stage;

The precipitations are collected in chronological order, so that the sieved quantum dots collected in the middle section account for 35-45% of the weight of the initial quantum dots, and are recorded as particle quantum dots in the middle section;

The precipitates are collected in sections in chronological order, so that the sieved quantum dots collected in the latter stage account for 25-35% of the weight of the initial quantum dots, and are recorded as small particle quantum dots in the latter stage.

In this embodiment, since the solubility of the organic ligands on the surface of the initial quantum dots in the first solvent is different, and the sedimentation effects of different insoluble solvents on the organic ligands are also significantly different. Because of this, it is difficult to calculate the amount of insoluble solvent by quantitative addition by choosing different organic ligands and first solvents. In this example, the samples obtained by particle size sieving are divided into large-particle quantum dots in the front section (accounting for 25-35% of the weight of the initial quantum dots) and medium-particle quantum dots in the middle section (accounting for the weight of the initial quantum dots) according to the order of flocculation and sedimentation. 35-45% of the initial quantum dots) and small particle quantum dots (25-35% of the initial quantum dot weight). In this embodiment, by slowly introducing an insoluble solvent into the initial quantum dot solution, and collecting flocculated and settled quantum dot particles in sections, quantum dot particles with different particle size ranges can be sieved. According to the size effect of quantum dots, the emission wavelength and half-peak width of quantum dots have a certain relationship with the particle size distribution of quantum dots, that is, the larger the quantum dot particle size, the longer the emission peak position, the smaller the size distribution, and the narrower the half-peak width. . After the quantum dot particles with larger size distribution are subjected to particle size sieving by the method of this embodiment, the collected flocculation precipitate is divided into a front part, a middle part and a rear part. The front part is the large particle quantum dots in the front part, the main emission peak of which has a red shift of 1-3 nm relative to the initial quantum dots, the emission peak position of the particle quantum dots in the middle part is almost unchanged, and the main emission peak of the small particle quantum dots in the latter part is about 2 nm. The blue shift is consistent with the size effect of quantum dots. As the size becomes larger or smaller, the emission wavelength shows a trend of red shift or blue shift; due to the quantum dot size sieving method, the size distribution deviation of quantum dots is reduced, Therefore, the half-peak widths of the collected three-stage quantum dot particles show a narrowing rule, and all have a narrowing trend of 2-3 nm.

In this example, before the quantum dot screening, the thickness of a fixed amount of initial quantum dots that did not dissolve in the solvent was pre-measured, and then in the process of adding an insoluble solvent to precipitate the initial quantum dots, by observing the precipitation The thickness estimates the proportion of the sieved quantum dots to the weight of the initial quantum dots, so that a predetermined weight of sieved quantum dots can be collected in different time periods.

In some specific embodiments, the precipitates are collected in sections in chronological order, so that the large particle quantum dots in the first section account for 30% of the weight of the initial quantum dots; the particle quantum dots in the middle section account for 30% of the weight of the initial quantum dots 40%; the small particle quantum dots in the latter stage account for 30% of the weight of the initial quantum dots. The size of the quantum dots obtained by the sieving method in this embodiment is uniform, and the size deviation of the quantum dots obtained at each stage is less than 5%.

In some specific embodiments, an initial quantum dot is provided, the position of the main emission peak of the initial quantum dot is 621 nm, the half-peak width is 27 nm, the particle size distribution of the quantum dot is 10±2 nm, and when the size deviation reaches 20%, That is, the difference between the quantum dots with the largest particle size and the smallest particle size can reach 4 nm; by using the quantum dot screening method of the present disclosure to sieve the initial quantum dots, the three-stage quantum dot particles can be obtained. The emission spectra of quantum dot particles were tested, and the emission wavelengths were 622nm, 621nm and 619nm, respectively, and the half-peak widths were 24nm, 25nm and 24nm, respectively. The particle size of the quantum dot particles is 10±0.7 nm, and the particle size of the latter quantum dot particles is 8.8±0.5 nm. The original quantum dot sample and the three groups of samples after sieving were used as light-emitting layer materials to prepare quantum dot light-emitting diode devices. The leakage current of the original sample device was relatively large at 1V voltage, and the photoelectric performance of the device was poor, and the current efficiency was 12cd. /A, mainly due to the large difference in particle size of quantum dots, and the existence of quantum dot particles with relatively large size differences, which aggravates the roughness of the film, and the film formation of the light-emitting layer is poor, resulting in poor interface contact and large leakage current of the device. . The roughness of the luminescent layer film prepared by the spin coating method using the front, middle and rear quantum dots after particle size sieving is obviously better than that of the original sample, mainly because the particle size of the quantum dots is closer and the film formation is better. And the leakage current of the device is significantly improved. The current efficiency of the device is 18cd/A, 17.5cd/A and 20cd/A, which is nearly 1.5 times higher than the original sample.

In some embodiments, during the particle size screening process of quantum dots, since the initial quantum dots and organic ligands are connected by weak coordination bonds, the process of flocculation and precipitation will lead to organic ligands coated on the surface of quantum dots. The body part falls off, thereby affecting the luminescence properties of the quantum dots. Based on this, after the precipitation is collected in stages, it is necessary to disperse the precipitation collected in stages into the first solvent and add organic ligands for mixing, so that the quantum dots whose ligands fall off during the sieving process can be combined with the organic ligands again. , sieved quantum dots with better performance were obtained.

Specifically, the large-particle quantum dots in the front section, the quantum dots in the middle section, and the small-particle quantum dots in the rear section are dispersed in the first solvent, respectively, to obtain a solution of large-particle quantum dots in the front section, a solution with particles in the middle section, and a rear section, respectively. A small particle quantum dot solution; then, respectively adding organic ligands to the front large particle quantum dot solution, the middle particle quantum dot solution and the back small particle quantum dot solution, so that the organic ligands are respectively connected to the The surface of the large particle quantum dots in the front section, the middle particle quantum dots in the middle section, and the small particle quantum dots in the rear section; finally, add the large particle quantum dot solution in the front section, the medium particle quantum dot solution in the middle section, and the small particle quantum dot solution in the rear section respectively. The insoluble solvent is added for cleaning to obtain a pure and uniformly sized solution of large particle quantum dots in the front part of the target, a solution of particle quantum dots in the middle part of the target, and a solution of small particle quantum dots in the rear part of the target.

In some embodiments, the initial quantum dots are II-VI compounds, III-V compounds, II-V compounds, III-VI compounds, IV-VI compounds, I-III-VI compounds, II -One or more of group IV-VI compounds and group IV elements, but not limited thereto.

Specifically, the initial quantum dots include, but are not limited to, nanocrystals of II-VI semiconductors, such as CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, PbS, PbSe, PbTe and other binary, Ternary and quaternary II-VI compounds; nanocrystals of III-V semiconductors, such as GaP, GaAs, InP, InAs and other binary, ternary, and quaternary III-V compounds. The initial quantum dots can also be core-shell quantum dots, and the cores constituting the core-shell quantum dots include CdSe, CdS, CdTe, CdSeTe, CdZnS, PbSe, ZnTe, CdSeS, PbS, PbTe, HgS, HgSe, At least one of HgTe, GaN, GaP, GaAs, InP, InAs, InZnP, InGaP and InGaN; the shell constituting the core-shell structure quantum dot contains at least one of ZnSe, ZnS and ZnSeS.

In some embodiments, the organic ligand is a long-chain organic compound or a short-chain organic compound containing at least one of a carboxyl group, an amine group, a thiol group, and a phosphine group, but is not limited thereto.

In some embodiments, the first solvent is one or more of saturated alkanes, unsaturated alkanes, saturated aromatic hydrocarbons and unsaturated aromatic hydrocarbons, but is not limited thereto. As an example, the first solvent is one or more of methylene chloride, chloroform, toluene, n-hexane, cyclohexane, n-heptane, n-octane, cycloheptane and dioxane, but not limited to this.

In some embodiments, the insoluble solvent is a polar solvent. As an example, the insoluble solvent is one or more of methanol, ethanol, isopropanol, n-butanol, n-amyl alcohol and ethyl acetate, but not limited thereto.

In some embodiments, a quantum dot light-emitting diode is also provided, which includes a quantum dot light-emitting layer, and the material of the quantum dot light-emitting layer is the sieved quantum dots described in the present disclosure.

In some specific embodiments, a quantum dot light-emitting diode is provided, as shown in FIG. 2 , which includes a substrate 10 , an anode 20 , a hole injection layer 30 , and a hole transport layer sequentially stacked from bottom to top 40. A quantum dot light-emitting layer 50, an electron transport layer 60 and a cathode 70, wherein the quantum dot light-emitting layer 50 is the sieved quantum dots described in this disclosure.

In this embodiment, since the size deviation of the sieved quantum dots obtained in the present disclosure can be controlled within 5%, and their sizes are uniform, the sieved quantum dots with uniform size are used as the material of the quantum dot light-emitting layer, which can effectively reduce the The roughness of the quantum dot light-emitting layer increases the flatness of its film formation, thereby effectively improving the photoelectric performance of the quantum dot light-emitting diode.

In some embodiments, the anode is selected from one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, and carbon nanotubes; the material of the hole injection layer is PEDOT:PSS , one or more of nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide and copper oxide; the hole transport layer material is one of PVK, Poly-TPD, CBP, TCTA and TFB or more; the material of the electron transport layer is one or more of n-type ZnO, TiO ₂ , SnO, Ta ₂ O ₃ , AlZnO, ZnSnO, InSnO, Alq ₃ , Ca, Ba, CsF, LiF, CsCO3; The cathode is selected from one or more of Al, Ca, Ba, and Ag.

A method for screening quantum dots, quantum dot light-emitting diodes and their properties of the present disclosure will be further explained below through specific embodiments:

In an embodiment of the present disclosure:

1. A method for screening quantum dots, comprising the following steps:

1), the initial red quantum dot CdZnSe/ZnSe/ZnS obtained by synthesis, the surface organic coating ligand is oleic acid;

2), the initial red quantum dots are concentrated, dispersed in 4ml n-octane solvent with a concentration of 100mg/ml, and in a state of constant stirring, slowly drip the insoluble solvent ethanol, when the quantum dot solution appears flocculation, Continue stirring to completely precipitate the large particles, then separate them by centrifugation, and then continue to add the insoluble solvent dropwise to the supernatant, repeat this several times, collect the 120 mg of quantum dots collected in the previous section, and add 5 ml of n-octane. Solvent and 1ml of oleic acid to obtain a quantum dot solution uniformly dispersed in n-octane solvent; then wash with ethanol once to remove excess impurities to obtain a pure monodisperse, uniform size front quantum dot solution.

3), according to the same operation as step 2), respectively collect 150 mg of the quantum dot solution in the middle section and 110 mg of the quantum dot solution in the rear section, and the weight loss is caused by the loss during the operation.

2. Quantum dot performance test:

The initial red quantum dots and the sieved quantum dots prepared in this example were characterized by scanning electron microscopy, and the results are shown in Figure 3-Figure 6. The emission spectrum was measured, and the results are shown in Figure 7. It can be seen from Figures 3 to 7 that the collected front quantum dots have PL=622nm, FWHM=24nm, and the particle size of the quantum dot particles is 11±0.5nm; the middle quantum dots are PL=621nm, FWHM=25nm, and the The particle size is 10±0.7nm;

The latter quantum dots are PL=619nm, FWHM=24nm, and the particle size of the quantum dot particles is 9.1±0.6nm; the PL=621nm, FWHM=27nm of the initial red quantum dots, and the particle size of the initial red quantum dots is 10±1.5nm, Dimensional deviation is 15%.

3. Performance test of quantum dot light-emitting diodes:

Using the original sample (initial red quantum dots) and the collected front, middle and back quantum dots as light-emitting layers to prepare light-emitting diode devices, the device structure and the selected functional layer materials are: ITO/PEDOT:PSS/TFB/QDs/ZnO/ Al; and the photoelectric properties of quantum dot light-emitting diode devices were tested, and the test results are shown in Table 1.

Table 1

	PL(nm)PL(nm)	FWHM(nm)FWHM(nm)	CE(cd/A)CE(cd/A)
原样品original sample	621621	2727	1212
前段样品Front-end sample	622622	24twenty four	1818
中段样品middle sample	621621	2525	17.517.5
后段样品back-end sample	619619	24twenty four	2020

As can be seen from Table 1, when the initial red quantum dots in this example are used as the material of the quantum dot light-emitting layer, the measured current efficiency of the quantum dot light-emitting diode is 12cd/A, and its photoelectric performance is poor, and when the In Example 1, when the sieved front-stage sample, middle-stage sample and rear-stage sample were used as quantum dot light-emitting layer materials, the current efficiencies of the quantum dot light-emitting diode devices were 18cd/A, 17.5cd/A and 20cd/A, respectively. The photoelectric efficiency is nearly 1.5 times higher than that of the original sample, which is mainly because the particle size of the sieved quantum dots is closer, and the film formation is better, so that the leakage current of the device is significantly improved.

In another embodiment of the present disclosure:

1. A method for sieving quantum dots, comprising the following steps:

1), the synthetically obtained green quantum dots CdZnSe/ZnS, PL=527nm, FWHM=29nm, the surface organic coating ligand is octanethiol, the particle diameter of the quantum dots is 8±1.2nm, and the size deviation is 15%;

2) Concentrate the green quantum dots, disperse them in 5ml n-octane solvent with a concentration of 80mg/ml, slowly add insoluble solvent ethanol dropwise under constant stirring, when the quantum dot solution appears flocculation, continue Stir to make the large particles completely precipitate, then separate them by centrifugation, and then add the insoluble solvent dropwise to the supernatant, repeat this several times, collect 110 mg of quantum dots collected in the previous section, and add 5 ml of n-octane solvent. and 0.5ml of octanethiol to obtain a quantum dot solution uniformly dispersed in the n-octane solvent; add ethanol to wash once, and wash away excess impurities to obtain a pure monodisperse, uniform size front quantum dot solution;

3), according to the same operation as step 2), respectively collect 140 mg of quantum dot solution in the middle and 130 mg of the latter part, and the weight loss is caused by the loss during the operation.

2. Quantum dot performance test:

The sieved quantum dots prepared in this example were characterized by emission spectrum and scanning electron microscope. The collected front-stage quantum dots were PL=529nm, FWHM=25nm, and the particle size of the quantum dot particles was 8.5±0.6nm; the middle-stage quantum dots were PL=527nm , FWHM=24nm, the particle size of quantum dot particles is 8±0.5nm; the latter quantum dot PL=525nm, FWHM=26nm, the particle size of quantum dot particles is 7.4±0.5nm.

3. Performance test of quantum dot light-emitting diodes:

Using the original sample (initial red quantum dots) and the collected front, middle and back quantum dots as light-emitting layers to prepare light-emitting diode devices, the device structure and the selected functional layer materials are: ITO/PEDOT:PSS/TFB/QDs/ZnO/ Al; and the photoelectric properties of quantum dot light-emitting diode devices were tested, and the test results are shown in Table 2.

Table 2

	PL(nm)PL(nm)	FWHM(nm)FWHM(nm)	CE(cd/A)CE(cd/A)
原样品original sample	527527	2929	4545
前段样品Front-end sample	529529	2525	7373
中段样品middle sample	527527	24twenty four	6262
后段样品back-end sample	525525	2626	6868

As can be seen from Table 2, when the initial green quantum dots in this example are used as the material of the quantum dot light-emitting layer, the measured current efficiency of the quantum dot light-emitting diode is 45cd/A, and its photoelectric performance is poor, and when this When the sieved front-stage sample, middle-stage sample and rear-stage sample were used as quantum dot light-emitting layer materials, the current efficiencies of the quantum dot light-emitting diode devices were 73cd/A, 68cd/A, and 62cd/A, respectively. Compared with the original sample, the efficiency is greatly improved, mainly because the particle size of the sieved quantum dots is closer, and the film formation is better, so that the leakage current of the device is significantly improved.

To sum up, the present disclosure gradually adds an insoluble solvent that is mutually soluble with the first solvent but immiscible with the organic ligand into the initial quantum dot solution. When the initial quantum dot solution begins to flocculate, continue to stir to make the large particles completely precipitate, and then separate them by centrifugation, and then continue to drop the supernatant with insoluble solvent, repeat this several times, segment Collect precipitates with similar particle sizes, and the size deviation of the isolated quantum dots can be controlled within 5%, so as to obtain quantum dot materials with uniform size; the quantum dots with uniform size are used as quantum dot light-emitting layer materials, The photoelectric performance of the quantum dot light-emitting diode can be effectively improved.

It should be understood that the application of the present disclosure is not limited to the above examples, and those of ordinary skill in the art can make improvements or transformations according to the above descriptions, and all these improvements and transformations should fall within the protection scope of the appended claims of the present disclosure.

Claims

A method for sieving quantum dots, comprising the steps of:

Dispersing the initial quantum dots with organic ligands connected on the surface in the first solvent to obtain the initial quantum dot solution;

The insoluble solvent is gradually added to the initial quantum dot solution and mixed, so that the initial quantum dots are gradually precipitated according to the order of particle size from large to small, and the precipitates are collected in sections in chronological order to obtain the sieved quantum dots, The insoluble solvent is miscible with the first solvent and immiscible with the organic ligand.
The sieving method of quantum dots according to claim 1, wherein the step of collecting the precipitates in chronological order to obtain the sieved quantum dots comprises:

The precipitation is collected in sections according to time sequence, so that the sieved quantum dots collected in the previous stage account for 25-35% of the weight of the initial quantum dots, and are recorded as large-particle quantum dots in the previous stage;

The precipitations are collected in chronological order, so that the sieved quantum dots collected in the middle section account for 35-45% of the weight of the initial quantum dots, and are recorded as particle quantum dots in the middle section;

The precipitates are collected in sections in chronological order, so that the sieved quantum dots collected in the latter stage account for 25-35% of the weight of the initial quantum dots, and are recorded as small particle quantum dots in the latter stage.
The method for sieving quantum dots according to claim 2, wherein the large particle quantum dots in the front section account for 30% of the weight of the initial quantum dots; the particle quantum dots in the middle section account for 40% of the weight of the initial quantum dots; Duan small particle quantum dots account for 30% of the initial quantum dot weight.
The sieving method of quantum dots according to claim 2, wherein, further comprises the step:

Disperse the large particle quantum dots in the front section, the middle particle quantum dots in the middle section, and the small particle quantum dots in the rear section in the first solvent, respectively, to obtain the large particle quantum dot solution in the front section, the middle particle quantum dot solution in the middle section, and the small particle quantum dots in the rear section. point solution;

Add organic ligands to the large particle quantum dot solution in the front section, the quantum dot solution in the middle section and the small particle quantum dot solution in the back section respectively, so that the organic ligands are connected to the large particle quantum dots in the front section and the particles in the middle section. The surface of quantum dots and the latter small particle quantum dots;

Then add an insoluble solvent to the large particle quantum dot solution in the front section, the quantum dot solution in the middle section and the small particle quantum dot solution in the back section respectively for cleaning to obtain the large particle quantum dot solution in the front section of the target and the quantum dot solution in the middle section of the target. And the small particle quantum dot solution in the rear segment of the target.
The method for sieving quantum dots according to any one of claims 1-4, wherein the initial quantum dots are II-VI compounds, III-V compounds, II-V compounds, III-VI compounds, IV- One or more of group VI compounds, group I-III-VI compounds, group II-IV-VI compounds and group IV elements.
The method for sieving quantum dots according to any one of claims 1-4, wherein the organic ligand is a long-chain organic substance or a short-chain organic substance containing at least one of a carboxyl group, an amine group, a sulfhydryl group and a phosphine group.
The screening method for quantum dots according to any one of claims 1-4, wherein the first solvent is one or more of saturated alkanes, unsaturated alkanes, saturated aromatic hydrocarbons and unsaturated aromatic hydrocarbons.
The sieving method for quantum dots according to any one of claims 1-4, wherein the first solvent is dichloromethane, chloroform, toluene, n-hexane, cyclohexane, n-heptane, n-octane, cycloheptane One or more of alkane and dioxane.
The sieving method of quantum dots according to any one of claims 1-4, wherein the insoluble solvent is one or more of methanol, ethanol, isopropanol, n-butanol, n-amyl alcohol and ethyl acetate .
A quantum dot light-emitting diode, comprising a cathode, an anode, and a quantum dot light-emitting layer disposed between the cathode and the anode, and the quantum dot light-emitting layer material is the sieved material of any one of claims 1-9. quantum dots.
The quantum dot light-emitting diode according to claim 10, wherein the anode is one or more of indium tin oxide, fluorine-doped tin oxide, indium zinc oxide, graphene, and carbon nanotubes.
The quantum dot light-emitting diode according to claim 10, wherein the cathode is one or more of Al, Ca, Ba, and Ag.
The quantum dot light emitting diode of claim 10, further comprising a hole injection layer, a hole transport layer and an electron transport layer.
The quantum dot light-emitting diode according to claim 13, wherein the material of the hole injection layer is one of PEDOT: PSS, nickel oxide, molybdenum oxide, tungsten oxide, vanadium oxide, molybdenum sulfide, tungsten sulfide, and copper oxide. one or more.
The quantum dot light-emitting diode according to claim 13, wherein the hole transport layer material is one or more of PVK, Poly-TPD, CBP, TCTA and TFB.
The quantum dot light-emitting diode according to claim 13, wherein the material of the electron transport layer is n-type ZnO, TiO2, SnO, Ta2O3, AlZnO, ZnSnO, InSnO, Alq3, Ca, Ba, CsF, LiF, CsCO3 one or more of.