CN110819348B - Green quantum dot, preparation method and application thereof - Google Patents

Green quantum dot, preparation method and application thereof Download PDF

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CN110819348B
CN110819348B CN201810904568.4A CN201810904568A CN110819348B CN 110819348 B CN110819348 B CN 110819348B CN 201810904568 A CN201810904568 A CN 201810904568A CN 110819348 B CN110819348 B CN 110819348B
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CN110819348A (en
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陈小朋
赵海洋
谢阳腊
苏叶华
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Najing Technology Corp Ltd
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Abstract

The invention discloses a green quantum dot, a preparation method and application thereof. The green quantum dot has CdSe/ZnSeXS1‑Xa/ZnS structure comprising: a CdSe core; ZnSeXS1‑XA shell layer coated on the periphery of the CdSe core, wherein 0<X is less than or equal to 1; a ZnS shell layer coated with ZnSeXS1‑XThe periphery of the shell layer. The green quantum dot has the characteristics of quantum efficiency of more than 90%, half-peak width of between 20 and 26nm, monodispersity and the like, and the QLED device based on the green quantum dot has the advantages of high external quantum efficiency, long device service life and the like.

Description

Green quantum dot, preparation method and application thereof
Technical Field
The invention relates to the technical field of functional materials, in particular to a green quantum dot, and a preparation method and application thereof.
Background
Quantum Dot (QD), a semiconductor nanocrystal with a size of 1-100 nm and Quantum confinement effect. Due to its special optical and optoelectronic properties, such as extremely wide absorption spectrum, very narrow emission spectrum, very high luminous efficiency, the electrical and optical properties can be significantly adjusted by adjusting the size of the quantum dots to adjust the corresponding band gaps of the quantum dots. Quantum dots have a wide application prospect in various elements such as light-emitting elements or photoelectric conversion elements, and are currently applied to the fields of display, illumination, solar energy, anti-counterfeiting, bioluminescence labeling and the like.
The quantum dot-based light-emitting diodes (QLEDs) have the advantages of low lighting voltage, good light-emitting monochromaticity, low energy consumption, capability of adjusting the size of the luminescent color through quantum dots, low-cost solution method preparation and the like, and have great application potential in the display field and the solid-state lighting field. However, from the current development results, there are two main synthetic methods for quantum dots used in green QLEDs:
although the fluorescence quantum efficiency of the green core-shell structure quantum dots synthesized by the traditional method, such as CdSe/ZnSe, CdSe/CdS, CdSe/ZnS and other core-shell structure quantum dots, can reach 50-80%, the structure has many defects. Taking the most commonly used CdSe core quantum dots as an example, the more suitable shell materials include ZnS, ZnSe and CdS. However, the inventors have found that the following problems exist:
(1) the lattice mismatch degree of ZnS and CdSe is high, and the surface of the core-shell material has large tension and defects, so that the shape distribution of CdSe/ZnS is irregular, and the fluorescence quantum efficiency of green quantum dots of the CdSe/ZnS structure is low;
(2) the lattice mismatch degree of CdS and CdSe is low, but CdS as a shell can only generate a very small potential barrier, and an electron wave function can be easily leaked to the surface of the shell, so that the CdSe/CdS structure is unstable;
(3) growing a ZnSe shell layer on the surface of a CdSe quantum dot often requires a higher reaction temperature, and it is difficult to satisfy both the stability and the optical performance of the quantum dot.
And (II) green quantum dots with alloy structures synthesized by a one-pot method. Such as: qianlie subject is set in CdSe @ ZnS alloy quantum dots reported in 2015, and the device result is 100 cd.m-2At brightness, the T50 lifetime is 90,000h, which is already satisfactory for commercial application, however, the half-peak width of the quantum dot material is close to 30nm, which greatly limits the application of the quantum dot material in the display field. In the previous work, the Lilinsong group in China and the Heesun Yang and Heeyeop Chae group in Korea have reported a half-peak width of about 22nm (considered as half-peak width in the industry)<26nm is the standard of monodispersity), and the EQE can reach more than 10 percent, but does not show good performance in the aspect of service life. The quantum dots with the CdSe @ ZnS/ZnS alloy structure have the advantages that the size of an alloyed CdSe @ ZnS core is generally 8-10 nm, and the comparison is realized on the basis of the large coreThe ideal quantum confinement effect inhibits the Auger effect of the quantum confinement effect under the action of an electric field, the thickness of the ZnS layer required by the shell layer is always required to be 3-5 nm or even thicker, and the ZnS with the thickness can greatly improve the starting voltage of the QLED, so that the aging process of the QLED device is accelerated, and the service life of the device cannot be ideal. In addition, in practical application, the problem of poor solubility of the green quantum dots with large particle size in high-viscosity ink used for printing is also found, which further limits the application prospect of the CdSe @ ZnS/ZnS green quantum dots with such alloy structures in QLEDs.
Therefore, the development of quantum dots which are suitable for QLEDs and have monodispersity, high EQE (external quantum efficiency) and long device life and can emit green light is very significant and has wide market prospect.
Disclosure of Invention
The invention mainly aims to provide a green quantum dot, a preparation method and an application thereof, and aims to solve the problems that the green quantum dot in the prior art is low in stability, quantum efficiency, device life and solubility in high-viscosity ink used for printing to different degrees.
To achieve the above object, according to one aspect of the present invention, there is provided a green quantum dot having CdSe/ZnSeXS1-Xa/ZnS structure comprising a CdSe core; ZnSeXS1-XA shell layer coated on the periphery of the CdSe core, wherein 0<X is less than or equal to 1; a ZnS shell layer coated with ZnSeXS1-XThe periphery of the shell layer.
Further, ZnSeXS1-XIn the shell layer, X is more than or equal to 0.2 and less than or equal to 1.
Further, CdSe core and ZnSeXS1-XCdSe/ZnSe composed of shell layerXS1-XThe particle size of the quantum dots is 5-9 nm, and the particle size of the green quantum dots is 8-14 nm.
Furthermore, the UV wavelength corresponding to the first exciton peak of the CdSe core is 495-545 nm.
Further, CdSe/ZnSeXS1-XThe quantum dots have the light-emitting wavelength PL of 496-556 nm, the half-peak width of 19-25 nm, and the preferred CdSe/ZnSeXS1-XThe half-peak width of the quantum dots is 19-22 nm.
Furthermore, the green quantum dots have the light-emitting wavelength PL of 490-550 nm and the half-peak width of 20-26nm, and the half-peak width of the green quantum dots is preferably 20-23 nm.
According to another aspect of the present invention, there is provided a method for preparing green quantum dots, comprising the steps of: s1, preparing CdSe quantum dots as CdSe cores; s2, forming ZnSe around the CdSe coreXS1-XShell layer to obtain CdSe/ZnSeXS1-XQuantum dots of which 0<X is less than or equal to 1; s3 in CdSe/ZnSeXS1-XForming a ZnS shell layer at the periphery of the quantum dot to obtain the green quantum dot according to any one of claims 1 to 6.
Further, step S2 further includes: s21, mixing a Zn source with a first ligand and a first organic solvent, and heating to 150-200 ℃ to obtain a mixed solution C; s22, mixing the Se source with a second organic solvent to obtain a mixed solution D; s23, mixing the S source with a third organic solvent to obtain a mixed solution E; s24, heating the mixed solution C to 280-310 ℃, adding the CdSe quantum dot solution containing CdSe quantum dots, the mixed solution D and the mixed solution E, and reacting for 10-60 min under heat preservation to obtain the solution containing CdSe/ZnSeXS1-XCdSe/ZnSe of quantum dotsXS1-XA quantum dot solution.
Further, step S3 further includes: s31, mixing a Zn source with a second ligand and a fourth organic solvent, and heating to 150-200 ℃ to obtain a mixed solution F; s32, mixing the S source with a fifth organic solvent to obtain a mixed solution G; s33, heating the mixed solution F to 280-310 ℃ under the protection of inert gas, and then adding CdSe/ZnSe into the mixed solutionXS1-XAnd (3) carrying out heat preservation reaction on the quantum dot solution and the mixed solution G for 10-60 min to obtain a green quantum dot solution containing green quantum dots.
Further, in step S2, ZnSe is preparedXS1-XIn the process of the shell layer, the molar ratio of Zn in the Zn source, Se in the Se source and S in the S source is 1: 0.1-1: 0-0.9.
Further, in step S3, the molar ratio of Zn in the Zn source to S in the S source in the process of preparing the ZnS shell layer is 1: 0.1-1.
Further, the molar ratio of the CdSe quantum dot core, Zn in the Zn source in step S2, and Zn in the Zn source in step S3 is 1:1 × 104～5×105:1×104～5×105。
According to another aspect of the present invention, there is provided a quantum dot light emitting diode using any one of the green quantum dots.
Furthermore, the external quantum efficiency of the quantum dot light emitting diode is more than 10%, and the external quantum efficiency of the quantum dot light emitting diode is 100 cd.m-2T50 life at luminance is 10000 hours or more.
According to another aspect of the present invention, there is provided a quantum dot composition comprising any one of the green quantum dots described above.
The application provides a catalyst having CdSe/ZnSeXS1-XThe green quantum dot with the/ZnS structure comprises a CdSe core and ZnSe sequentially coated on the periphery of the CdSe coreXS1-XA shell layer and a ZnS shell layer of 0<X≤1。ZnSeXS1-XThe lattice matching degree of the ZnSe and the CdSe in the coating is higher, a good alloying structure can be formed between the ZnSe and the CdSe, and the outer ZnS can improve the coating stability. Therefore, a certain thickness of ZnSe is firstly coated on the CdSe coreXS1-XThe quantum dots are used as shell layers and are coated with ZnS, so that a perfect core-shell structure can be formed in the whole synthesis process of the quantum dots, and the stability of the core and the monodispersity of the quantum dots are improved; and by selecting CdSe with different absorption wavelengths as cores and adjusting the reactivity and the coating dosage of precursors of Se and S, the position of the emission wavelength can be easily regulated and controlled, and CdSe/ZnSe with high optical quality (the quantum efficiency is more than 90 percent and the half-peak width is less than 26 nm) is finally obtainedXS1-XGreen quantum dots of/ZnS structure.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present invention will be described in detail with reference to examples.
As described in the background art, the green quantum dots in the prior art have problems of low stability, quantum efficiency, device lifetime, and the like. In order to solve the above problems, the present invention provides a green quantum dot having CdSe/ZnSeXS1-Xthe/ZnS structure specifically comprises: a CdSe core; ZnSe coated on the periphery of CdSe coreXS1-XShell layer of which 0<X is less than or equal to 1; and coating with ZnSeXS1-XA ZnS shell layer at the periphery of the shell layer.
The green quantum dot provided by the application is formed by coating ZnSe with a certain thickness on a CdSe coreXS1-XAnd as a shell layer, the ZnS is coated. The CdSe quantum dots have wider absorption wavelength band, higher emission intensity and better light stability, and the emission and absorption wavelengths can be controlled by adjusting the size of the CdSe quantum dots; ZnSeXS1-XThe lattice matching degree of the ZnSe and the CdSe in the quantum dot is high, and a good alloying structure can be formed with the outer ZnS, so that a perfect core-shell structure can be formed in the whole synthesis process of the quantum dot, and the stability of the core and the monodispersity of the quantum dot are improved; the ZnS can provide an energy level range for doping of various metals and transition metal ions, and a shell layer is epitaxially grown on the quantum dot core to passivate the surface, so that the luminous efficiency and the optical stability are greatly improved, and the non-toxic ZnS shell layer is coated on the outermost layer and is environment-friendly. CdSe is taken as a core, and the position of the emission wavelength can be easily regulated and controlled by regulating the reactivity and the coating dosage of precursors of Se and S, so that CdSe/ZnSe with high optical quality (the efficiency is more than 90 percent and the half-peak width is less than 25 nm) is finally obtainedXS1-XGreen quantum dots of/ZnS structure.
In order to improve the reactivity of Se and S and further more easily regulate the position of the emission wavelength of the quantum dots and improve the optical quality of the quantum dots, in a preferred embodiment, the ZnSe isXS1-XIn the shell layer, X is more than or equal to 0.2 and less than or equal to 1.
In a preferred embodiment, the CdSe core and ZnSeXS1-XComposition of shell layerCdSe/ZnSe ofXS1-XThe average particle size of the quantum dots is 5-9 nm, and the average particle size of the green quantum dots is 8-14 nm. The particle size of the quantum dots can realize a relatively ideal quantum confinement effect, and inhibit the Auger effect of the quantum dots under the action of an electric field, so that the starting voltage of the QLED device manufactured by the quantum dots is reduced, the aging process of the QLED device is slowed down, and the QLED device with a longer service life is obtained.
In order to improve the light emission monochromaticity of the green quantum dots and improve the optical performance of the green quantum dots, in a preferred embodiment, the UV wavelength corresponding to the first exciton peak of the CdSe core is 495-545 nm.
The half-peak width represents the particle size distribution of the quantum dots, influences the purity of the luminescent color of the quantum dots, and in order to improve the luminescent monochromaticity and the optical performance of the green quantum dots, in a preferred embodiment, CdSe/ZnSeXS1-XThe quantum dots have the light-emitting wavelength PL of 496-556 nm and the half-peak width of 19-25 nm, and CdSe/ZnSe is preferredXS1-XThe half-peak width of the quantum dots is 19-22 nm.
Preferably, the green quantum dots have an emission wavelength PL (maximum emission peak position) of 490 to 550nm, a half-peak width of 20 to 26nm, and preferably a half-peak width of 20 to 23 nm.
In another exemplary embodiment, the present application provides a method for preparing green quantum dots, comprising the steps of: s1, preparing CdSe quantum dots as CdSe cores; s2, forming ZnSe around the CdSe coreXS1-XShell layer to obtain CdSe/ZnSeXS1-XQuantum dots of which 0<X is less than or equal to 1; s3 in CdSe/ZnSeXS1-XAnd forming a ZnS shell layer at the periphery of the quantum dot to obtain the green quantum dot.
According to the preparation method of the green quantum dots, the CdSe quantum dots are firstly prepared through a two-step coating method and are used as CdSe cores, and ZnSe is sequentially coated and formed on the peripheries of the CdSe coresXS1-XShell layer (0)<X is less than or equal to 1) and a ZnS shell layer. The prepared green quantum dot has the characteristic of different absorption wavelengths from the CdSe core, and then the ZnSe is adjustedXS1-XReactivity of precursors of Se and S in shell layer andthe coating amount is further adjusted and controlled, the position of the emission wavelength is finally adjusted, the green quantum dots which have high optical quality and are high in brightness service life and high in quantum efficiency in the QLED device are finally obtained, the green quantum dots obtained by the preparation method are high in light-emitting wavelength controllability, the kilogram-level quantum dot production scale can be realized, the photobleaching resistance and the air stability are high, the QLED device can be prepared in the air, and the requirements on equipment and the preparation cost during preparation of the green QLED are greatly reduced. The preparation method is simple and reliable to operate, good in controllability, suitable for large-scale production and has a high value for application and development of quantum dots.
In a preferred embodiment, the step S1 includes: s11, mixing the Cd source with a third ligand and a sixth organic solvent, and heating to 160-180 ℃ under the protection of inert gas to obtain a mixed solution A; s12, mixing the Se source with a seventh organic solvent to obtain a mixed solution B; and S13, under the protection of inert gas, heating the mixed solution A to 220-240 ℃, then adding the mixture B into the mixed solution A, and carrying out heat preservation reaction for 10-20 min to obtain the CdSe quantum dot solution containing CdSe quantum dots.
In order to fully disperse the Cd source and the Se source in the organic solvent so as to mix the Cd source and the Se source to prepare the CdSe quantum dots, in a preferred embodiment, in the step S11, the mixed solution A is obtained by magnetic stirring, wherein the stirring speed is 60 rpm/min; the mixed solution C is obtained by dispersing Se powder in a seventh organic solvent through ultrasonic oscillation for 2 min.
In order to remove the organic solvent, the ligand and the like remaining after the preparation of the CdSe quantum dot, and improve the purity of the CdSe quantum dot solution, so as to facilitate the subsequent coating process to achieve the purpose of further improving the optical performance of the green quantum dot, in a preferred embodiment, in step S1, after obtaining the CdSe quantum dot solution, the method further includes a process of purifying the CdSe quantum dot solution, specifically as follows: and (3) placing the CdSe quantum dot solution and n-hexane in a first liquid separation device, washing for 2-3 times by using methanol, transferring the upper layer solution into a centrifugal device, adding acetone, centrifuging, taking out a solid precipitate, and placing the solid precipitate in an Octadecene (ODE) solution for dissolving to obtain the purified CdSe quantum dot solution.
In a preferred embodiment, the step S2 includes: s21, mixing a Zn source with a first ligand and a first organic solvent, and heating to 150-200 ℃ under the protection of inert gas to obtain a mixed solution C; s22, mixing the Se source with a second organic solvent to obtain a mixed solution D; s23, mixing the S source with a third organic solvent to obtain a mixed solution E; s24, heating the mixed solution C to 280-310 ℃ under the protection of inert gas, adding the CdSe quantum dot solution, the mixed solution D and the mixed solution E, and reacting for 10-60 min under heat preservation to obtain the product containing CdSe/ZnSeXS1-XCdSe/ZnSe of quantum dotsXS1-XA quantum dot solution.
In order to fully disperse the Zn source, the Se source and the S source in the organic solvent so as to be convenient for the mixture of the Zn source, the Se source and the S source to prepare CdSe/ZnSeXS1-XAnd (4) shell layer. In step S11, the mixed solution C is obtained by magnetic stirring, and the stirring speed is 60 rpm/min; and dispersing Se powder and S powder in corresponding organic solvents by ultrasonic oscillation for 2min to obtain mixed solutions D and E.
For the removal preparation of CdSe/ZnSeXS1-XOrganic solvent and ligand left after quantum dots increase CdSe/ZnSeXS1-XThe purity of the quantum dot solution is favorable for the subsequent coating process, and the purpose of improving the optical performance of the green quantum dots is achieved. In a preferred embodiment, after step S2 and before step S3, the method further comprises the step of adding CdSe/ZnSeXS1-XThe process of purifying the quantum dot solution specifically comprises the following steps: mixing CdSe/ZnSeXS1-XPutting the quantum dot solution and acetone into a centrifugal device, centrifuging, taking out solid precipitate, putting the solid precipitate into an ODE solution for dissolving to obtain purified CdSe/ZnSeXS1-XA quantum dot solution.
In a preferred embodiment, the step S3 includes: s31, mixing a Zn source with a second ligand and a fourth organic solvent, and heating to 150-200 ℃ under the protection of inert gas to obtain a mixed solution F; s32, mixing the S source with a fifth organic solvent to obtain a mixed solution G; s33, under the protection of inert gas, the mixed solution F is liftedHeating to 280-310 ℃, and then adding CdSe/ZnSe into the mixtureXS1-XAnd (3) carrying out heat preservation reaction on the quantum dot solution and the mixed solution G for 10-60 min to obtain a green quantum dot solution containing green quantum dots.
In order to sufficiently disperse the Zn source and the S source in the organic solvent so that the both are mixed to prepare the ZnS shell layer. In step S31, the mixed solution F is obtained by magnetic stirring, and the stirring speed is 60 rpm/min; the mixed solution G is obtained by dispersing S powder in the corresponding organic solvent through ultrasonic oscillation for 2 min.
Preparation of Green Quantum dots (CdSe/ZnSe) for EliminationXS1-X/ZnS quantum dots), organic solvent and ligand remaining after the preparation, and the like, and improves CdSe/ZnSeXS1-XIn a preferred embodiment, after step S3, a purification process of the green quantum dot solution is further included, specifically as follows: and placing the green quantum dot solution and acetone in a centrifugal device, centrifuging, taking out a solid precipitate, and placing the precipitate in a toluene solution for dissolving to obtain a purified green quantum dot solution.
In a preferred embodiment, the Cd source includes, but is not limited to, cadmium acetate dihydrate, cadmium oxide, or cadmium dimethyl, preferably cadmium acetate dihydrate; sources of Zn include, but are not limited to, zinc acetate; the Se source is selected from Se powder; the S source is selected from S powder; the first ligand, the second ligand and the third ligand are respectively and independently selected from olive oil or oleic acid, preferably oleic acid; the first organic solvent, the fourth organic solvent, the sixth organic solvent and the seventh organic solvent are respectively and independently one or more selected from liquid paraffin, oleylamine and octadecene, and preferably are octadecene; the second organic solvent, the third organic solvent and the fifth organic solvent are selected from one or more of tributyl phosphate, tributyl phosphine, triphenyl phosphine, tri-n-octyl phosphine, diphenyl phosphine or dioctyl phosphine, and preferably trioctyl phosphine and/or tributyl phosphine.
The ligand can adjust the dynamic rate of adsorption and falling of crystal faces of the quantum dots and the coordination solvent, so that the growth speed of a certain crystal face of the quantum dots is higher than that of other crystal faces, the shape of the quantum dots is changed, the crystal form is controlled, and the energy level and the energy gap width of the quantum dots are matched with the energy level and the energy gap width of zinc oxide nanocrystals (used as an electron transmission material) in the QLED device, namely an ordered stepped structure is formed.
In a preferred embodiment, in step S2, ZnSe is preparedXS1-XIn the process of the shell layer, the molar ratio of Zn in the Zn source, Se in the Se source and S in the S source is 1: 0.1-1: 0-0.9. Therefore, the stability of the CdSe core and the ZnS shell layer can be further improved, the integral lattice mismatch degree of the green quantum dots is reduced, and the quantum efficiency of the green quantum dots is improved. Meanwhile, the half-peak width of the green quantum dots is prevented from being influenced by the excessively thick shell layer, so that the service life of the quantum dots is further ensured.
In order to form a ZnS shell layer with a suitable thickness such that the green quantum dots satisfy high stability, high quantum efficiency and half-peak width with monodispersity at the same time, in a preferred embodiment, in step S3, the molar ratio of Zn in the Zn source and S in the S source in the process of preparing the ZnS shell layer is 1: 0.1-1.
In a preferred embodiment, the molar ratio of the CdSe quantum dot core, Zn in the Zn source in step S2, and Zn in the Zn source in step S3 is 1:1 × 104～5×105:1×104～5×105. The particle size of each layer can be controlled by controlling the molar ratio of each element forming the core, the shell layer and the shell layer, so that a better quantum confinement effect is realized, and a more ideal service life of the device is obtained.
In another exemplary embodiment, the present application provides a quantum dot light emitting diode using any of the green quantum dots described above.
The quantum dot light-emitting diode provided by the application has the external quantum efficiency of more than 10 percent and is 100 cd.m-2T50 (time for the luminance of the device to decrease to 50% of the initial) lifetime of 10000 hours or more at luminance can satisfy the demand of commercial application.
In another exemplary embodiment, the present application provides a quantum dot composition comprising any one of the green quantum dots described above. The quantum dot composition may be a quantum dot ink for preparing a QLED device.
The present application is described in further detail below with reference to specific examples, which should not be construed as limiting the scope of the invention as claimed.
Synthesis of CdSe quantum dot cores
1) 0.533gCd (Ac)2)2·2H2O (2mmol), 2.28g of Oleic Acid (OA) (8mmol) and 12g of Octadecene (ODE) are weighed in sequence and placed in a 100mL three-necked bottle, a magneton is added, the temperature of the system is raised to 170 ℃ under the protection of nitrogen, and then magnetic stirring is carried out, wherein the stirring speed is 60 rpm/min;
2) 39.5mg of Se powder (0.5mmol) is weighed and added into 2mLODE, and the Se powder is dispersed by ultrasonic oscillation for 2 min;
3) under the protection of nitrogen, raising the temperature of the system to 230 ℃, quickly injecting 1mLSe-ODE mixed solution, keeping the temperature for reaction for 15min, and measuring a first exciton peak UV (ultraviolet) of CdSe to 488 nm;
4) and then, dropwise adding 0.1mL of Se-ODE mixed solution in batches, wherein the dropwise adding interval is 10min each time, sampling and monitoring after 5min, and stopping the reaction after the first UV exciton peak reaches a target position. According to the method, a CdSe core with a first exciton peak of 495nm is synthesized and used for synthesizing green quantum dots;
5) pouring the prepared CdSe core into a separating funnel, adding 20mL of n-hexane and 70mL of methanol, uniformly mixing, removing the lower layer of methanol, repeating the operation, washing for 2-3 times by using the methanol, and keeping the volume of the solution at the upper layer between 10-15 mL;
6) transferring the upper layer solution containing the CdSe core into a centrifuge tube, adding 30-40 mL of acetone, uniformly mixing, centrifuging at the speed of 4900rpm/min for 3min, discarding the liquid solution, and dissolving the solid precipitate by using ODE to obtain a purified CdSe quantum dot solution containing the CdSe quantum dots;
7) and centrifuging at 4900rpm for 3min, taking ODE solution, and measuring the OD of the first exciton peak for later use.
According to the mode, by controlling the dropping amount of the Se-ODE, the CdSe quantum dot core with the UV wavelength of 495-545 nm corresponding to the first exciton peak can be synthesized.
Example 1
Preparation of CdSe/ZnSe0.5S0.5/ZnS quantum dot
(1)CdSe/ZnSe0.5S0.5Synthesis of quantum dots
1) Weighing 0.183g of zinc acetate (1mmol), 1.12g of OA (4mmol) and 5g of ODE in sequence, placing the weighed materials in a 100mL three-necked bottle, adding magnetons, raising the temperature of the system to 160 ℃ under the protection of nitrogen, then carrying out magnetic stirring at the stirring speed of 60rpm/min, and introducing nitrogen to exhaust air and acetic acid for at least 0.5 h;
2) weighing 20mg Se powder (0.25mmol), adding 0.5mL of TOP (trioctylphosphine), and dissolving by ultrasonic wave; weighing 8mg of S powder (0.25mmol), adding 0.5mL of TBP (tributylphosphine), and dissolving by ultrasonic wave; subsequently, Se-TOP and S-TBP are mixed for standby;
3) after the system was deoxygenated, the temperature of the system was raised to 305 ℃ and the purified CdSe quantum dot solution (CdSe, UV-495 nm, OD-50, 25nmol) was added;
4) injecting the mixed solution of Se-TOP and S-TBP prepared in the step 2, carrying out heat preservation reaction for 20min, sampling every 5min and monitoring PL and half peak width to finally obtain CdSe/ZnSe0.5S0.5The PL of the quantum dot is 496nm, the half-peak width is 19nm, and the average size of the mirror is 6.2 nm;
5) removing the heat source, cooling the system to below 100 ℃, and cooling;
6) the prepared CdSe/ZnSe0.5S0.5Transferring the quantum dots to a 50mL centrifuge tube, adding 30mL acetone, mixing uniformly, centrifuging at 4900rpm/min for 3min, discarding the liquid solution, air drying the solid, and dissolving with ODE to obtain the product containing CdSe/ZnSe0.5S0.5CdSe/ZnSe of quantum dots0.5S0.5A quantum dot solution;
7) mixing CdSe/ZnSe0.5S0.5And centrifuging the ODE solution of the quantum dots for 3min at 4900rpm, and taking the upper ODE solution for later use.
(2)CdSe/ZnSe0.5S0.5Synthesis of/ZnS quantum dot
1) 0.183g of ZnAc2(1mmol), 1.12g OA (4mmol) and 5g ODE are weighed in turn and placed in a 100mL three-necked flask, a magneton is added, the temperature of the system is raised to 160 ℃ under the protection of nitrogen, and thenThen magnetic stirring is carried out, the stirring speed is 60rpm/min, and the time for introducing nitrogen to exhaust air and acetic acid is at least 0.5 h;
2) weighing 8mg of S powder (0.25mmol), adding 0.5mL of TBP, and dissolving by ultrasonic treatment;
3) after the system is deoxygenated, the temperature of the system is raised to 305 ℃, and the purified CdSe/ZnSe is added0.5S0.5A quantum dot solution;
4) injecting the S-TBP solution prepared in the step 2, reacting for 20min, sampling every 5min to monitor PL and half peak width, and finally CdSe/ZnSe0.5S0.5The PL of the quantum dot is 491nm, the half-peak width is 20nm, the QY (quantum efficiency) is 95.9%, the average size of an electron microscope is 8.0nm, and the maximum soluble quantum dot of 200mg in corresponding 1mL of printing ink;
5) removing the heat source, cooling the system to below 100 ℃, and cooling;
6) transferring the prepared quantum dot stock solution into a 50mL centrifuge tube, adding 30mL acetone, mixing uniformly, centrifuging at 4900rpm/min for 3min, discarding the liquid solution, air drying the solid, dissolving with toluene to obtain the purified CdSe/ZnSe-containing solution0.5S0.5CdSe/ZnSe of/ZnS quantum dots0.5S0.5a/ZnS quantum dot solution;
7) will contain CdSe/ZnSe0.5S0.5The toluene solution of/ZnS was centrifuged at 4900rpm/min for 3min, and the upper toluene solution was collected and the OD at UV450nm was measured and stored for further use.
Example 2
Preparation of CdSe/ZnSe0.8S0.2/ZnS quantum dot
In contrast to example 1, the CdSe core used in step (1) was 545nm, OD 50, 25 nmol; ZnAc2The dosage is reduced to 0.8mmol, the dosage of Se powder is increased to 0.4mmol, and the Se powder is dissolved in 0.8mL of TOP solution; reducing the dosage of S powder to 0.1mmol, and dissolving in 0.2mL TBP; the temperature of the precursor solution (mixed solution C) for preparing the Zn source is 150 ℃, and CdSe/ZnSe is synthesized0.8S0.2The temperature of the quantum dots is 280 ℃, the reaction is carried out for 10min under the condition of heat preservation, and the CdSe/ZnSe is measured0.8S0.2The PL of the quantum dot is 556nm, the half-peak width is 22nm, and the average size of an electron microscope is 8.7 nm;
in the step (2), ZnAc is added2The dosage is increased to 2mmol, the dosage of OA is increased to 8mmol, the dosage of S powder is increased to 1mmol, the mixture is dissolved in 2ml of TBP, the temperature of precursor solution (mixed solution F) for preparing the Zn source is 150 ℃, and the CdSe/ZnSe is synthesized0.8S0.2The reaction temperature of the/ZnS quantum dots is 280 ℃, the heat preservation reaction is carried out for 10min, and finally the CdSe/ZnSe0.8S0.2The PL of/ZnS was 550nm, the half-peak width was 23nm, the QY was 91.8%, and the average size of electron microscopy was 12.0 nm. The highest soluble 83mg quantum dots in the corresponding 1mL printing ink.
Example 3
Preparation of CdSe/ZnSe0.2S0.8/ZnS quantum dot
In contrast to example 1, the CdSe core used in step (1) was UV 538nm, OD 50, 25 nmol; ZnAc2Increasing the dosage to 1.2mmol, reducing the dosage of Se powder to 0.1mmol, and dissolving in 0.2ml of TOP solution; the dosage of S powder is reduced to 0.4mmol, and the S powder is dissolved in 0.8mL of LTBP; the temperature of the precursor solution (mixed solution C) for preparing the Zn source is 200 ℃, and CdSe/ZnSe is synthesized0.2S0.8The temperature of the quantum dots is 310 ℃, the reaction is carried out for 60min under the condition of heat preservation, and the CdSe/ZnSe is measured0.2S0.8The PL of the quantum dot is 534nm, the half-peak width is 22nm, and the average size of an electron microscope is 7.6 nm;
ZnAc is subjected to the step (2)2The dosage is increased to 1.5mmol, the dosage of OA is increased to 6mmol, the dosage of S powder is increased to 0.5mmol, the mixture is dissolved in 1ml of TBP, the temperature for preparing the precursor solution (mixed solution F) of the Zn source is 200 ℃, and CdSe/ZnSe is synthesized0.8S0.2The reaction temperature of the/ZnS quantum dots is 310 ℃, the heat preservation reaction is carried out for 60min, and finally the CdSe/ZnSe0.2S0.8The PL of/ZnS was 529nm, the half-peak width was 23nm, QY was 96.7%, and the average size of electron microscopy was 10.2 nm. The highest soluble 156mg quantum dots in the corresponding 1mL printing ink.
Example 4
Preparation of CdSe/ZnSe0.4S0.6/ZnS quantum dot
In contrast to example 1, the CdSe core used in step (1) had UV 523nm, OD 50, 25 nmol; the dosage of Se powder is reduced to 0.2mmol, and the Se powder is dissolved in 0.4ml of TOP solution; the amount of S powder was increased to 0.3mmol and dissolved in 0.6 mLTBP; the CdSe/ZnSe is measured0.4S0.6The PL of the quantum dot is 526nm, the half-peak width is 21nm, and the average size of an electron microscope is 7.1 nm;
ZnAc is subjected to the step (3)2The dosage is increased to 1.2mmol, the dosage of OA is increased to 4.8mmol, the dosage of S powder is increased to 0.4mmol, the S powder is dissolved in 0.8ml of TBP, and finally CdSe/ZnSe0.4S0.6The PL of/ZnS was 520nm, the half-peak width was 22nm, the QY was 94.8%, and the average size of electron microscopy was 9.3 nm. The highest soluble 178mg quantum dots in the corresponding 1mL printing ink.
Example 5
Preparation of CdSe/ZnSe/ZnS quantum dots
In contrast to example 1, the CdSe core used in step (1) was UV 525nm, OD 50, 25 nmol; the dosage of Se powder is 0.5mmol, and the Se powder is dissolved in 1ml of LTBP solution; keeping the temperature for reaction for 60min, and measuring that the PL of the CdSe/ZnSe quantum dots is 530nm, the half-peak width is 20nm, and the average size of an electron microscope is 6.4 nm;
ZnAc is subjected to the step (2)2The dosage is increased to 1.2mmol, the dosage of OA is increased to 4.8mmol, the dosage of S powder is 1mmol, the mixture is dissolved in 2ml of TBP, the reaction is carried out for 60min under the condition of heat preservation, the PL of the CdSe/ZnSe/ZnS is 524nm, the half-peak width is 23nm, the QY is 93.6%, and the average size of an electron microscope is 10.8 nm. The highest soluble 138mg quantum dot in the corresponding 1mL printing ink.
Example 6 is based on 520nm CdSe/ZnSe0.4S0.6QLED of/ZnS quantum dot
The CdSe/ZnSe with the wavelength of 520nm prepared in example 4 was selected0.4S0.6The method is characterized in that the/ZnS quantum dots are used for preparing the QLED device, the whole process is carried out in the air atmosphere, and the specific operation steps are as follows: on a glass substrate with an ITO coating, a PSS solution (Baytron PVPAl 4083, filtered through 0.45mmN66 filter paper) was spin coated with PEDOT within 1 minute, a chlorobenzene solution of PVK, CdSe/ZnSe, was spin coated sequentially within 45 seconds at 2000rpm/min for 10 minutes at 140 deg.C0.4S0.6The preparation method comprises the steps of preparing ethanol solution of/ZnS quantum dots and ZnO nanocrystals, plating a 100nm Ag layer by using a vacuum evaporation method, and finally sealing the device in organic glass by using ultraviolet curing resin. Among them, CdSe/ZnSe0.4S0.6/ZnS quantum dot layerIs 40 nm. Detected based on CdSe/ZnSe0.4S0.6The External Quantum Efficiency (EQE) of the air-processed QLED of the/ZnS quantum dot can reach 18 percent and is 100 cd.m-2The T50 life of the luminance was 100,000 hours or more.
Comparative example 1
520nm CdSe @ ZnS/ZnS Quantum Dots synthesized according to the literature (K.Lee, et al, Over 40cd/A Efficient Green Quantum Dot electrolyte Device sharing Uniform Large-Sized Quantum Dots, ACS Nano,8,4893(2014) doi:10.1021/nn500852g) with an electron-microscopic average size of 9.5nm and a final CdSe @ ZnS/ZnS electron-microscopic average size of 12.7 nm. Up to 43mg of quantum dots are soluble in the corresponding 1ml of printing ink.
Comparative example 2
535nm CdSe @ ZnS quantum dots synthesized according to the methods of the literature (Y.Yang, et al, High-efficiency light-emitting devices based on quantum dots with patterned nanoparticles, Nature photon, 9,259(2015), doi:10.1038/NPHOTON.2015.36), wherein the average electron microscopic size of CdSe @ ZnS is 8.2 nm. The highest possible soluble 195mg quantum dots in the corresponding 1ml printing ink.
Comparative example 3:
preparation of CdSe/ZnS quantum dots
Unlike example 1, only S-TBP (0.5 mmoleS in 1mL TBP) was injected in step (2), and the final CdSe/ZnS had a PL of 526nm, a half-peak width of 38nm, a QY of 56.8%, and an electron-microscopic average size of 6.8 nm.
Comparative example 4: QLED based on 520nm CdSe @ ZnS/ZnS quantum dots of comparative example 1
Through detection, the QLED prepared in the air atmosphere based on the 520nmCDSe @ ZnS/ZnS quantum dots of the comparative example 1 (the preparation process is the same as the example 6) has the External Quantum Efficiency (EQE) of 12 percent and 100 cd.m-2The T50 lifetime at brightness was about 1000 hours.
Comparative example 5: QLED based on 535nm CdSe @ ZnS quantum dots of comparative example 2
The detection proves that the External Quantum Efficiency (EQE) of the QLED prepared by 535nmCDSe @ ZnS/ZnS quantum dots based on the comparative example 2 in the air atmosphere can reach 8 percent, and 100 cd.m-2T50 Life of luminanceAbout 8000 hours
From the above description, it can be seen that the above-described embodiments of the present invention achieve the following technical effects: by adopting the green quantum dot provided by the application, the CdSe quantum dot is prepared firstly through a two-step coating method, is taken as a CdSe core, and is sequentially coated on the periphery of the CdSe core to form ZnSeXS1-XShell layer (0)<X is less than or equal to 1) and a ZnS shell layer. The prepared green quantum dots have the characteristics of different absorption wavelengths of CdSe cores, and then the ZnSe is adjustedXS1-XThe position of emission wavelength of the precursor of Se and S in the shell layer is regulated and controlled by the reactivity and the coating dosage of the precursor of Se and S in the shell layer, and finally the green quantum dot with high optical quality (the quantum efficiency is more than 90 percent, the half-peak width is less than 26 nm) and high quantum efficiency (more than 80 percent) is obtained, and the electron microscope size of the particle is between 8 and 12 nm. The green quantum dots obtained by the preparation method have high controllability of light-emitting wavelength, can realize the production scale of kilogram-level quantum dots, have high photobleaching resistance and air stability, can meet the requirement of preparing devices in the air, and greatly reduce the requirement on equipment and the preparation cost during the preparation of green QLEDs. The preparation method is simple and reliable to operate, good in controllability, suitable for large-scale production and has a high value for application and development of quantum dots. Meanwhile, the QLED prepared by the green quantum dots has ideal device life (100 cd.m)-2Luminance T50 lifetime greater than 10000 hours) and quantum efficiency (greater than 10%), meeting the needs of commercial applications.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (16)

1. A green quantum dot, wherein the green quantum dot has CdSe/ZnSeXS1-Xa/ZnS structure comprising:
a CdSe core;
ZnSeXS1-Xa shell layer coated on the periphery of the CdSe core, wherein X is more than or equal to 0.2<1；
A ZnS shell layer covering the ZnSeXS1-XThe periphery of the shell layer;
the CdSe core and the ZnSeXS1-XCdSe/ZnSe composed of shell layerXS1-XThe particle size of the quantum dots is 5-9 nm; the half-peak width of the green quantum dots is 20-26 nm.
2. The green quantum dot according to claim 1, wherein the particle size of the green quantum dot is 8 to 14 nm.
3. The green quantum dot of claim 2, wherein the first exciton peak of the CdSe core corresponds to a UV wavelength of 495-545 nm.
4. The green quantum dot of claim 3, wherein the CdSe/ZnSeXS1-XThe quantum dots have an emission wavelength PL of 496-556 nm and a half-peak width of 19-25 nm.
5. The green quantum dot of claim 4, wherein the CdSe/ZnSeXS1-XThe half-peak width of the quantum dots is 19-22 nm.
6. The green quantum dot according to any one of claims 1 to 4, wherein the green quantum dot has an emission wavelength PL of 490 to 550 nm.
7. The green quantum dot according to claim 6, wherein the green quantum dot has a half-peak width of 20-23 nm.
8. A preparation method of a green quantum dot, wherein the green quantum dot is the green quantum dot of any one of claims 1 to 7, and the method comprises the following steps:
s1, preparing CdSe quantum dots as CdSe cores;
s2, forming ZnSe around the CdSe coreXS1-XShell layer to obtain CdSe/ZnSeXS1-XQuantum dots of which 0.2. ltoreq. X<1；
S3, in the CdSe/ZnSeXS1-XForming a ZnS shell layer at the periphery of the quantum dot to obtain the green quantum dot as claimed in any one of claims 1 to 7.
9. The method for preparing as claimed in claim 8, wherein the step S2 further comprises:
s21, mixing a Zn source with a first ligand and a first organic solvent, and heating to 150-200 ℃ to obtain a mixed solution C;
s22, mixing the Se source with a second organic solvent to obtain a mixed solution D;
s23, mixing the S source with a third organic solvent to obtain a mixed solution E;
s24, heating the mixed solution C to 280-310 ℃, adding a CdSe quantum dot solution containing CdSe quantum dots, the mixed solution D and the mixed solution E, and reacting for 10-60 min under heat preservation to obtain the solution containing CdSe/ZnSeXS1-XCdSe/ZnSe of quantum dotsXS1-XA quantum dot solution.
10. The method for preparing as claimed in claim 9, wherein the step S3 further comprises:
s31, mixing a Zn source with a second ligand and a fourth organic solvent, and heating to 150-200 ℃ to obtain a mixed solution F;
s32, mixing the S source with a fifth organic solvent to obtain a mixed solution G;
s33, heating the mixed solution F to 280-310 ℃ under the protection of inert gas, and then adding the CdSe/ZnSeXS1-XAnd (3) carrying out heat preservation reaction on the quantum dot solution and the mixed solution G for 10-60 min to obtain a green quantum dot solution containing the green quantum dots.
11. According toThe production method according to any one of claims 9 to 10, wherein in the step S2, the ZnSe is producedXS1-XIn the process of the shell layer, the molar ratio of Zn in the Zn source, Se in the Se source and S in the S source is 1: 0.2-1: 0-0.8, and the molar ratio is not equal to 1:1: 0.
12. The method according to claim 11, wherein in step S3, the molar ratio of Zn in the Zn source and S in the S source in the production of the ZnS shell layer is 1:0.1 to 1.
13. The preparation method of claim 12, wherein the molar ratio of the CdSe quantum dot core, Zn in the Zn source in the step S2 and Zn in the Zn source in the step S3 is 1:1 x 104～5×105:1×104～5×105。
14. A quantum dot light-emitting diode characterized in that the green quantum dot according to any one of claims 1 to 7 is used.
15. The qd-led of claim 14, wherein the external quantum efficiency of the qd-led is greater than 10%, and the qd-led is at 100 cd-m-2T50 life at luminance is 10000 hours or more.
16. A quantum dot composition, wherein the quantum dot composition comprises the green quantum dot of any one of claims 1 to 7.
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