WO2020029780A1

WO2020029780A1 - Green quantum dot, preparation method and application thereof

Info

Publication number: WO2020029780A1
Application number: PCT/CN2019/097048
Authority: WO
Inventors: 陈小朋; 赵海洋; 谢阳腊; 苏叶华
Original assignee: 纳晶科技股份有限公司
Priority date: 2018-08-09
Filing date: 2019-07-22
Publication date: 2020-02-13
Also published as: CN110819348B; CN110819348A

Abstract

Provided is a green quantum dot, a preparation method, and an application thereof. The green quantum dot has a CdSe/ZnSe _XS _1-X/ZnS structure, comprising: a CdSe core; a ZnSe _XS _1-X shell coated on the periphery of the CdSe core, where 0<X≤1; and a ZnS shell coated on the periphery of the ZnSe _XS _1-X shell. The green quantum dot has characteristics of a quantum efficiency greater than 90%, a half-peak width between 20-26 nm, monodispersity, and the like. A QLED device employing the green quantum dot has the advantages of high external quantum efficiency and a long device lifetime.

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, a preparation method thereof and an application thereof.

Background technique

Quantum dots (QDs), that is, semiconductor nanocrystals that are usually between 1 and 100 nm in size and have quantum confinement effects. Due to its special optical and optoelectronic properties, such as extremely wide absorption spectrum, very narrow emission spectrum, and high luminous efficiency, by adjusting the size of the quantum dot to adjust the corresponding band gap of the quantum dot, its electrical properties can be significantly adjusted. , Optical characteristics, etc. Quantum dots have a wide range of application prospects in a variety of elements such as light-emitting elements or photoelectric conversion elements. At present, they have been used in many fields such as display, lighting, solar energy, anti-counterfeiting, and biological fluorescent labeling.

Quantum dot-based light-emitting diodes (QLEDs) have the advantages of low lighting voltage, good light-emitting monochromaticity, low energy consumption, and light-emitting colors that can be prepared by quantum dot size adjustment and low-cost solution methods. The display field and solid-state lighting field have huge application potential. However, from the current research and development results, there are two main synthesis methods of quantum dots for green QLED:

(1) Green core-shell structure quantum dots synthesized by traditional methods, such as CdSe / ZnSe, CdSe / CdS, CdSe / ZnS and other core-shell structure quantum dots. Although their fluorescence quantum efficiency can reach 50-80%, this structure exists Many disadvantages. Taking the most commonly used CdSe core quantum dots as an example, the more suitable shell materials are ZnS, ZnSe, and CdS. However, the inventor found the following problems:

(1) The lattice mismatch of ZnS and CdSe is high, and there are large tension and defects on the surface of the core-shell material, which makes the morphology distribution of CdSe / ZnS irregular, which in turn leads to the green quantum dots of CdSe / ZnS structure. Low fluorescence quantum efficiency;

(2) The lattice mismatch between CdS and CdSe is low, but CdS as a shell can only generate a small potential barrier, and the electron wave function can be easily leaked to the surface of the shell, which leads to the CdSe / CdS structure not stable;

(3) Growing a ZnSe shell on the surface of a CdSe quantum dot often requires a higher reaction temperature, and it is difficult to satisfy the stability and optical performance of the quantum dot at the same time.

(2) There are also green quantum dots with alloy structures synthesized by a one-pot method. For example: CdSe @ ZnS alloy quantum dots reported by Qian Lei's research group in 2015. The device results are at a brightness of 100cd · m ^-2 and a T50 life of 90,000h, which can meet commercial applications. However, this kind of quantum dot material The half-width of the peak is close to 30nm, which greatly limits its application in the display field. In the previous work, Li Linsong's research group in China and Heesun Yang and Heeyeop Chae's research group in South Korea also reported CdSe @ with a half-peak width of about 22 nm (the industry believes that the half-peak width <26 nm is the standard for monodispersity). The quantum dots of ZnS / ZnS alloy structure, and EQE can reach more than 10%, but they have not shown good performance in terms of life. This is mainly due to the quantum dots of this type of CdSe @ ZnS / ZnS alloy structure. The alloyed CdSe @ ZnS core size is generally between 8 and 10 nm, and it is necessary to achieve a more ideal quantum confinement based on such a large core. Effect, suppressing the Auger effect under the action of the electric field. The thickness of the ZnS layer required for its shell layer is usually 3 to 5 nm or even thicker, and such a thickness of ZnS will greatly increase the startup voltage of QLEDs, thereby accelerating QLED The aging process of the device cannot obtain the ideal device life. In addition, it has been found in practical applications that large-sized green quantum dots have poor solubility in high-viscosity inks used for printing, which will further limit the CdSe @ ZnS / ZnS green quantum dots of such alloy structures. Application prospects in QLED.

Therefore, developing a class of quantum dots that can emit green light for QLED with monodispersity, high EQE (external quantum efficiency), and high device lifetime is very meaningful and has broad market prospects.

Summary of the invention

The main purpose of the present invention is to provide a green quantum dot, a preparation method thereof, and an application thereof, in order to solve the problems of stability, quantum efficiency, device life, and solubility in high-viscosity inks used for printing of green quantum dots in the prior art. There are problems with lower levels.

In order to achieve the above object, according to an aspect of the present invention, a green quantum dot is provided. The green quantum dot has a CdSe / ZnSe _X S _1-X / ZnS structure, including a CdSe core; a ZnSe _X S _1-X shell layer, CdSe core is coated on the periphery, where 0 <X≤1; ZnS shell is coated on the periphery of ZnSe _X S _1-X shell.

Further, in the ZnSe _X S _1-X shell layer, 0 <X <1.

Further, in the ZnSe _X S _1-X shell layer, 0.2 ≦ _X ≦ 1.

Further, in the ZnSe _X S _1-X shell layer, 0.2 ≦ _X <1.

Further, the particle size of the CdSe / ZnSe _X S _1-X quantum dot composed of the CdSe core and the ZnSe _X S _1-X shell layer is 5-9 nm, and the particle size of the green quantum dot is 8-14 nm.

Further, the UV wavelength corresponding to the first exciton peak of the CdSe core is 495-545 nm.

Further, the emission wavelength PL of the CdSe / ZnSe _X S _1-X quantum dot is 496 to 556 nm, and the half-width of the peak is 19 to 25 nm. Preferably, the half-width of the CdSe / ZnSe _X S _1-X quantum dot is 19 to 22 nm.

Further, the emission wavelength PL of the green quantum dots is 490 to 550 nm, and the half-peak width is 20 to 26 nm. The half-width width of the green quantum dots is preferably 20 to 23 nm.

According to another aspect of the present invention, a method for preparing green quantum dots is provided, including the following steps: S1, preparing CdSe quantum dots as a CdSe core; S2, forming a ZnSe _X S _1-X shell layer on the periphery of the CdSe core, CdSe / ZnSe _X S _1-X quantum dots are obtained, where 0 <X≤1; S3, a ZnS shell is formed on the periphery of the CdSe / ZnSe _X S _1-X quantum dots, and the green quantum dots are obtained.

Further, 0 <X <1.

Further, 0.2 ≦ X ≦ 1.

Further, 0.2 ≦ X <1.

Further, step S2 further includes: S21, mixing the Zn source with the first ligand and the first organic solvent, and heating up to 150-200 ° C to obtain a mixed solution C; S22, mixing the Se source with the second organic solvent, A mixed solution D is obtained; S23, the S source is mixed with a third organic solvent to obtain a mixed solution E; S24, the mixed solution C is heated to 280-310 ° C, and then a CdSe quantum dot solution containing CdSe quantum dots is added thereto, and mixed The solution D and the mixed solution E were incubated for 10 to 60 minutes to obtain a CdSe / ZnSe _X S _1-X quantum dot solution containing CdSe / ZnSe _X S _1-X quantum dots.

Further, step S3 further includes: S31, mixing the Zn source with the second ligand and the fourth organic solvent, and heating up to 150-200 ° C to obtain a mixed solution F; S32, mixing the S source with the fifth organic solvent, A mixed solution G is obtained; S33. Under the protection of an inert gas, the mixed solution F is heated to 280-310 ° C, and then a CdSe / ZnSe _X S _1-X quantum dot solution and a mixed solution G are added thereto, and the reaction is held for 10 to 60 minutes. A green quantum dot solution containing green quantum dots was obtained.

Further, in step S2, in the process of preparing the ZnSe _X S _1-X 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 to 1: 0 to 0.9.

Further, in step S3, the molar ratio of Zn in the Zn source to S in the S source during the preparation of the ZnS shell is 1: 0.1 to 1.

Further, the molar ratio of the CdSe quantum dot core, the Zn in the Zn source in step S2 and the Zn in the Zn source in step S3 is 1: 1 × 10 ⁴ to 5 × 10 ⁵ : 1 × 10 ⁴ to 5 × 10 ⁵ .

According to another aspect of the present invention, a quantum dot light emitting diode is provided, using any one of the above-mentioned green quantum dots.

Further, the external quantum efficiency of the quantum dot light emitting diode is greater than 10%, and the T50 lifetime of the quantum dot light emitting diode at a brightness of 100 cd · m ^-2 is greater than or equal to 10,000 hours.

According to another aspect of the present invention, a quantum dot composition is provided. The quantum dot composition includes any one of the green quantum dots described above.

The present application provides a green quantum dot having a CdSe / ZnSe _X S _1-X / ZnS structure, which includes a CdSe core, and a ZnSe _X S _1-X shell layer and a ZnS shell layer sequentially covering the periphery of the CdSe core. Where 0 <X≤1. In ZnSe _X S _1-X , the lattice matching between ZnSe and CdSe is high, and it can form a good alloyed structure with the outer layer of ZnS, and the outer layer of ZnS can improve the stability of the coating. Therefore, by covering the core of CdSe with a certain thickness of ZnSe _X S _1-X as a shell, and then coating ZnS, it can ensure that the quantum dots form a perfect core-shell structure during the entire synthesis process, which improves the stability of the core. And the monodispersity of quantum dots; and by selecting CdSe with different absorption wavelengths as the nucleus, adjusting the reactivity and coating amount of the precursors of Se and S, it is relatively easy to adjust the position of their emission wavelengths, and finally get high Green quantum dots with CdSe / ZnSe _X S _1-X / ZnS structure with optical quality (quantum efficiency above 90% and half-value width below 26 nm).

detailed description

It should be noted that, in the case of no conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be described in detail with reference to the following embodiments.

As described in the background art, green quantum dots in the prior art have problems with low degrees of stability, quantum efficiency, and device life. In order to solve the above problems, the present invention provides a green quantum dot, which has a CdSe / ZnSe _X S _1-X / ZnS structure, and specifically includes: a CdSe core; and a ZnSe _X S ₁ covering a periphery of the CdSe core. _{An X} shell layer, where 0 < _X ≦ 1; and a ZnS shell layer covering the periphery of the ZnSe _X S _1-X shell layer.

The green quantum dots provided in the present application are coated with ZnSe _X S _1-X with a certain thickness on the CdSe core as a shell, and then coated with ZnS. CdSe quantum dots have a wider absorption wavelength band, higher emission intensity, and better light stability. The emission and absorption wavelengths can be controlled by adjusting their size; the lattices of ZnSe and CdSe in ZnSe _X S _1-X The degree of matching is high, and it can form a good alloyed structure with the outer layer of ZnS. Therefore, it can ensure that the quantum dots form a perfect core-shell structure during the entire synthesis process, which improves the stability of the core and the monodispersity of the quantum dots. ; ZnS can provide a range of energy levels for the doping of various metals and transition metal ions, and at the same time epitaxially grow a shell on the quantum dot core to passivate the surface, thereby greatly improving the luminous efficiency and optical stability. The toxic ZnS shell is coated on the outermost layer and is environmentally friendly. With CdSe as the nucleus, and by adjusting the reactivity of the precursors of Se and S and the amount of coating, the position of its emission wavelength can be adjusted relatively easily, and finally high optical quality (efficiency above 90%, half-width at 25nm) Below) green quantum dots with CdSe / ZnSe _X S _1-X / ZnS structure.

In order to better balance the alloyed structure with the outer layer ZnS and the lattice matching with CdSe, 0 <X <1 is preferred in the ZnSe _X S _1-X shell layer. In addition, in order to further reduce the degree of lattice mismatch between CdSe and ZnS, and thereby more easily eliminate internal defects of the quantum dots and improve their optical quality, in a preferred embodiment, the above-mentioned ZnSe _X S _1-X In the shell layer, 0.2≤X≤1; more preferably 0.2≤X <1.

In one embodiment, the average particle size of the CdSe / ZnSe _X S _1-X quantum dots composed of the CdSe core and the ZnSe _X S _1-X shell is 5-9 nm, and the average particle size of the green quantum dots is 8-14 nm. . The particle size of the quantum dot can achieve a more ideal quantum confinement effect, suppress the Auger effect of the quantum dot under the action of the electric field, thereby reducing the startup voltage of the QLED device made by the quantum dot, slowing the aging process of the QLED device, and obtaining the life. Longer QLED devices.

In order to improve the luminescence monochromaticity of the green quantum dots and the optical performance of the green quantum dots, in one 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 and affects the purity of the quantum dots' emission color. In order to improve the luminosity and optical properties of the green quantum dots, in a preferred embodiment, CdSe / ZnSe _X S ₁ The emission wavelength PL of the _-X quantum dot is 496 to 556 nm, and the half-peak width is 19 to 25 nm. In a preferred embodiment, the half-peak width of the CdSe / ZnSe _X S _1-X quantum dot is 19-22 nm.

In one embodiment, the emission wavelength PL (maximum emission peak position) of the green quantum dot is 490 to 550 nm, and the half-peak width is 20 to 26 nm. In a preferred embodiment, the half-peak width of the green quantum dot is 20 to 23 nm.

In another typical embodiment, the present application provides a method for preparing green quantum dots, including the following steps: S1, preparing CdSe quantum dots as CdSe cores; S2, forming ZnSe _X S _{1- The X-} shell layer is obtained to obtain CdSe / ZnSe _X S _1-X quantum dots, where 0 < _X ≦ 1; S3, a ZnS shell layer is formed on the periphery of the CdSe / ZnSe _X S _1-X quantum dots to obtain the green quantum dots described above.

The green quantum dot preparation method provided in the present application firstly prepares a CdSe quantum dot by a two-step coating method, and uses the CdSe quantum dot as a CdSe core, and sequentially coats a ZnSe _X S _1-X shell (0 <X ≤1) and ZnS shell. This makes the prepared green quantum dots have different absorption wavelength characteristics from that of CdSe cores, and then adjusts the reactivity and coating amount of the precursors of Se and S in the ZnSe _X S _1-X shell to regulate its emission. The position of the wavelength finally results in green quantum dots with high optical quality, high brightness lifetime and high quantum efficiency in QLED devices. The green quantum dots obtained by this preparation method have high controllability of the emission wavelength and can achieve kilogram level. The production scale of quantum dots, and its photobleaching resistance and high air stability, can meet the requirements for the preparation of QLED devices in the air, which greatly reduces the equipment requirements and preparation costs when preparing green QLEDs. The preparation method has simple and reliable operation, good controllability, is suitable for large-scale production, and has great value for the development of quantum dot applications.

In a preferred embodiment, the above-mentioned step S1 includes: S11, mixing the Cd source with the third ligand and the sixth organic solvent, and raising the temperature to 160-180 ° C under the protection of an inert gas to obtain a mixed solution A; S12 S13 is mixed with a seventh organic solvent to obtain a mixed solution B; S13, under the protection of an inert gas, the mixed solution A is heated to 220-240 ° C, and then the mixture B is added thereto, and the reaction is held for 10-20 minutes to obtain CdSe quantum dot solution of CdSe quantum dots.

In order to make the Cd source and the Se source sufficiently dispersed in the organic solvent, so as to prepare the CdSe quantum dots by mixing the two, in a preferred embodiment, in the above step S11, the mixed solution A is obtained by magnetic stirring, wherein the stirring speed is 60 rpm / min; mixed solution C was obtained by dispersing Se powder in a seventh organic solvent by ultrasonic vibration for 2 min.

In some embodiments, in order to remove the organic solvents and ligands remaining after the CdSe quantum dots are prepared, and to improve the purity of the CdSe quantum dot solution, so as to facilitate the subsequent coating process and thereby further improve the optical properties of the green quantum dots, In a preferred embodiment, after the CdSe quantum dot solution is obtained in step S1, the process of purifying the CdSe quantum dot solution is further included as follows: the CdSe quantum dot solution and n-hexane are placed in a first liquid separation In the device, wash with methanol 2 to 3 times, move the upper solution to a centrifugal device, add acetone, remove the solid precipitate after centrifugation, and dissolve it in a non-polar solvent such as octadecene (ODE). After purification, CdSe quantum dot solution. The specific purification method is not limited to this, and other purification methods may also be adopted.

In a preferred embodiment, the above step S2 includes: S21, mixing the Zn source with the first ligand and the first organic solvent, and heating up to 150-200 ° C under the protection of an inert gas to obtain a mixed solution C; S22 S source is mixed with a second organic solvent to obtain a mixed solution D; S23, S source is mixed with a third organic solvent to obtain a mixed solution E; S24, under the protection of an inert gas, the mixed solution C is heated to 280-310 CdSe, and then add CdSe quantum dot solution, mixed solution D and mixed solution E, and hold the reaction for 10-60 minutes to obtain a CdSe / ZnSe _X S _1-X quantum dot solution containing CdSe / ZnSe _X S _1-X quantum dots.

In some embodiments, in order to sufficiently disperse the Zn source, the Se source, and the S source in an organic solvent, so that the three are mixed to prepare a CdSe / ZnSe _X S _1-X shell layer, in the above step S11, the mixed solution C is passed through a magnetic force. Obtained by stirring, the stirring speed is 60 rpm / min; the Se powder and the S powder are dispersed in their corresponding organic solvents by ultrasonic vibration for 2 min to obtain mixed solutions D and E.

In order to remove the organic solvents and ligands remaining after the preparation of CdSe / ZnSe _X S _1-X quantum dots, the purity of the CdSe / ZnSe _X S _1-X quantum dot solution was improved to facilitate the subsequent coating process and improve the green quantum dots. The purpose of optical performance. In a preferred embodiment, after step S2 and before step S3, a process of purifying the CdSe / ZnSe _X S _1-X quantum dot solution is further included as follows: CdSe / ZnSe _X S _1-X quantum The spot solution and acetone were placed in a centrifugal device. After centrifugation, the solid precipitate was taken out and dissolved in an ODE solution to obtain a purified CdSe / ZnSe _X S _1-X quantum dot solution.

In a preferred embodiment, the above-mentioned step S3 includes: S31, mixing the Zn source with the second ligand and the fourth organic solvent, and heating up to 150-200 ° C under the protection of an inert gas to obtain a mixed solution F; S32 S source is mixed with a fifth organic solvent to obtain a mixed solution G; S33, under the protection of an inert gas, the mixed solution F is heated to 280-310 ° C, and then a CdSe / ZnSe _X S _1-X quantum dot solution is added thereto It is mixed with the solution G and incubated for 10 to 60 minutes to obtain a green quantum dot solution containing green quantum dots.

In some embodiments, in order to sufficiently disperse the Zn source and the S source in an organic solvent, so that the two can be mixed to prepare a ZnS shell layer, in the above step S31, the mixed solution F is obtained by magnetic stirring, and the stirring speed is 60 rpm / min. ; The mixed solution G was obtained by dispersing S powder in its corresponding organic solvent by ultrasonic shaking for 2 min.

In order to remove the organic solvents and ligands remaining after the preparation of green quantum dots (CdSe / ZnSe _X S _1-X / ZnS quantum dots), the purity of the CdSe / ZnSe _X S _1-X quantum dot solution was improved to realize the improvement of green quantum dots. The purpose of dot optical performance, in a preferred embodiment, after step S3, the purification process of the green quantum dot solution is further included as follows: the green quantum dot solution and acetone are placed in a centrifugal device, and after centrifugation The solid precipitate was taken out, and the precipitate was dissolved in a toluene solution 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 dimethyl cadmium, preferably cadmium acetate dihydrate; the Zn source includes, but is not limited to, zinc acetate; the source of Se is selected from Se powder ; S source is selected from S powder; the first ligand, the second ligand and the third ligand are independently selected from olive oil or oleic acid, preferably oleic acid; the first organic solvent, the fourth organic solvent, the first The six organic solvents and the seventh organic solvent are each independently selected from one or more of liquid paraffin, oleylamine, and octadecene, and preferably all are octadecene; the second organic solvent, the third organic solvent, and the fifth organic solvent The solvent is selected from one or more of tributyl phosphate, tributylphosphine, triphenylphosphine, tri-n-octylphosphine, diphenylphosphine or dioctylphosphine, preferably trioctylphosphine and / or Tributylphosphine.

The ligand can adjust the dynamic rate of the adsorption and shedding of the quantum dot crystal plane and the coordination solvent, so that one crystal plane of the quantum dot can grow faster than other crystal planes, change the shape of the quantum dot, control the crystal form, and make the energy level of the quantum dot. And the forbidden band width can be matched with the forbidden band width of the energy level of zinc oxide nanocrystals (as electron transport material) in the QLED device, that is, an orderly stepped structure is formed.

In a preferred embodiment, in step S2, during the preparation of the ZnSe _X S _1-X 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 to 1: 0 to 0.9. This can further improve the stability of the CdSe core and the ZnS shell, reduce the overall lattice mismatch of the green quantum dots, and further improve the quantum efficiency of the green quantum dots. At the same time, the half-peak width of the green quantum dots is prevented from being affected by an excessively thick shell layer, thereby further ensuring the lifetime of the quantum dots.

In order to form a ZnS shell layer with a suitable thickness, so that the green quantum dots simultaneously satisfy high stability, high quantum efficiency, and half-peak width with monodispersity, in a preferred embodiment, in step S3, the ZnS shell layer is prepared. In the process, the molar ratio of Zn in the Zn source to S in the S source is 1: 0.1 to 1.

In a preferred embodiment, the molar ratio of the CdSe quantum dot core, the Zn in the Zn source in step S2 and the Zn in the Zn source in step S3 is 1: 1 × 10 ⁴ to 5 × 10 ⁵ : 1 × 10 ⁴ to 5 × 10 ⁵ . By controlling the molar ratio of each element in the core, the first shell layer and the second shell layer, the size or overall particle size of each layer can be controlled, thereby achieving a better quantum confinement effect and obtaining a more ideal device life.

In another typical embodiment, the present application provides a quantum dot light emitting diode, which adopts any one of the above-mentioned green quantum dots or a green quantum dot prepared by any of the above methods. The quantum dot light emitting diode includes an anode, a light emitting layer, and a cathode. The light emitting layer includes any of the green quantum dots described above, and optionally further includes an electron or hole functional layer.

In some embodiments, the quantum dot light emitting diode provided in the present application, the external quantum efficiency of the quantum dot light emitting diode is greater than 10%, and the T50 of the quantum dot light emitting diode at a brightness of 100 cd · m ^-2 (the device brightness is reduced to an initial 50% Time) life is greater than or equal to 10,000 hours, which can meet the needs of commercial applications.

In another typical embodiment, a display device is provided, including at least one quantum dot light emitting diode.

In another typical embodiment, the present application provides a quantum dot composition including any one of the above-mentioned green quantum dots. The quantum dot composition may be a quantum dot ink for making a QLED device.

The following further describes the present application in detail with reference to specific embodiments, which cannot be understood as limiting the scope of protection claimed by the present application.

Synthesis of CdSe Quantum Dot Nuclei

1) Weigh 0.533g of Cd (Ac ₂ ) ₂ · 2H ₂ O (2mmol), 2.28g of oleic acid (OA) (8mmol), and 12g of octadecene (ODE) in order and place them in a 100mL three-necked bottle, add Magnet, increase the temperature of the system to 170 ° C under the protection of nitrogen, and then perform magnetic stirring at a stirring speed of 60 rpm / min;

2) Weigh 39.5mg of Se powder (0.5mmol), add it to 2mLODE, and sonicate for 2min to disperse it;

3) Under the protection of nitrogen, raise the temperature of the system to 230 ° C., quickly inject 1 mL of the Se-ODE mixed solution, and hold the reaction for 15 minutes to measure the first exciton peak UV of CdSe = 488 nm;

4) Then 0.1 mL of Se-ODE mixed solution is added dropwise in portions, and the dropwise addition interval is 10 minutes. After 5 minutes, the sample is monitored. After the first exciton peak of UV reaches the target position, the reaction is stopped. According to this method, a CdSe core with a first exciton peak of 495 nm was synthesized for the synthesis of green quantum dots;

5) Pour the prepared CdSe core into a separatory funnel, add 20 mL of n-hexane and 70 mL of methanol, mix well, remove the lower layer of methanol, repeat the operation, and wash with methanol 2 to 3 times until the volume of the upper layer solution is 10 ~ 15mL;

6) Transfer the upper solution containing the CdSe core to a centrifuge tube, add 30 to 40 mL of acetone, mix well, centrifuge at 4900 rpm / min for 3 minutes, discard the liquid solution, dissolve the solid precipitate with ODE, and obtain purified CdSe quantum dot solution containing CdSe quantum dots;

7) Centrifuge at 4900 rpm for 3 min, take the ODE solution, measure the first exciton peak optical density (OD), and reserve.

In this way, by controlling the amount of Se-ODE added, a CdSe quantum dot core with a UV wavelength of 495-545 nm corresponding to the first exciton peak can be synthesized.

Example 1

Preparation of CdSe / ZnSe _0.5 S _0.5 / ZnS quantum dots

(1) Synthesis of CdSe / ZnSe _0.5 S _0.5 quantum dots

1) Weigh 0.183g zinc acetate (1mmol), 1.12g OA (4mmol), and 5g ODE in a 100mL three-necked flask, add magnets, and increase the temperature of the system to 160 ° C under the protection of nitrogen. Then magnetic stirring is performed, the stirring speed is 60 rpm / min, and the time of exhausting nitrogen and acetic acid for at least 0.5h;

2) Weigh 20 mg of Se powder (0.25 mmol), add 0.5 mL of TOP (trioctylphosphine), and dissolve it with ultrasound; weigh 8 mg of S powder (0.25 mmol), and add 0.5 mL of TBP (tributylphosphine) ), Sonicate to dissolve it; then, mix Se-TOP and S-TBP and set aside;

3) After deoxidizing the system, raise the temperature of the system to 305 ° C, and add the purified CdSe quantum dot solution (CdSe, UV = 495nm, OD = 50, 25nmol);

4) Inject the mixed solution of Se-TOP and S-TBP prepared in step 2 and incubate for 20 minutes. Sample and monitor the PL and half-peak width every 5 minutes. The final PL of CdSe / ZnSe _0.5 S _0.5 quantum dots is 496 nm, half The peak width is 19nm and the average mirror size is 6.2nm;

5) Remove the heat source and cool down the system to below 100 ℃;

6) Transfer the prepared CdSe / ZnSe _0.5 S _0.5 quantum dots to a 50 mL centrifuge tube, add 30 mL of acetone, mix well, centrifuge at 4900 rpm / min for 3 minutes, discard the liquid solution, and dry the solid. with ODE dissolved to obtain comprising CdSe / ZnSe _{_0.5} S _0.5 quantum dot CdSe / ZnSe _{_0.5} S _0.5 quantum dot solution;

7) Centrifuge the ODE solution of CdSe / ZnSe _0.5 S _0.5 quantum dots at 4900 rpm for 3 min, and take the upper layer of ODE solution for later use.

(2) Synthesis of CdSe / ZnSe _0.5 S _0.5 / ZnS quantum dots

1) Weigh 0.183g ZnAc ₂ (1mmol), 1.12g OA (4mmol), and 5g ODE in a 100mL three-necked flask, add magnets, and raise the temperature of the system to 160 ° C under the protection of nitrogen. Then magnetic stirring is performed, the stirring speed is 60 rpm / min, and the time of exhausting nitrogen and acetic acid for at least 0.5h;

2) Weigh 8mg of S powder (0.25mmol), add 0.5mL of TBP, and dissolve it with ultrasound;

3) After deoxidizing the system, raise the temperature of the system to 305 ° C, and add the purified CdSe / ZnSe _0.5 S _0.5 quantum dot solution;

4) The S-TBP solution prepared in step 2 was injected and reacted for 20 minutes. The PL and half-peak width were sampled every 5 minutes. The final PL of CdSe / ZnSe _0.5 S _0.5 / ZnS quantum dots was 491 nm, and the half-peak width was 20 nm. QY ( Quantum efficiency) is 95.9%, the average size of the electron microscope is 8.0nm, and the maximum dissolvable 200mg quantum dots in the corresponding 1mL printing ink;

5) Remove the heat source and cool down the system to below 100 ℃;

6) Transfer the prepared quantum dot stock solution to a 50 mL centrifuge tube, add 30 mL of acetone, mix well, centrifuge at 4900 rpm / min for 3 min, discard the liquid solution, dry the solid, and dissolve it in toluene. comprising CdSe / ZnSe _{_0.5} S _0.5 / ZnS quantum dots obtained after purification CdSe / ZnSe _{_0.5} S _0.5 / ZnS quantum dot solution;

7) The toluene solution containing CdSe / ZnSe _0.5 S _0.5 / ZnS was centrifuged at a speed of 4900 rpm / min for 3 minutes, the upper toluene solution was taken, and the OD value at UV 450 nm was measured and stored for future use.

Example 2

Preparation of CdSe / ZnSe _0.8 S _0.2 / ZnS quantum dots

The difference from Example 1 is that the CdSe core used in step (1) is UV = 545nm, OD = 50, 25nmol _{; the} amount of ZnAc ₂ is reduced to 0.8mmol, the amount of Se powder is increased to 0.4mmol, and it is dissolved in 0.8mL TOP Solution; the amount of S powder was reduced to 0.1mmol and dissolved in 0.2mL of TBP; the temperature of preparing the Zn source precursor solution (mixed solution C) was 150 ° C, and the temperature for synthesizing CdSe / ZnSe _0.8 S _0.2 quantum dots was 280 ° C; After 10 minutes of reaction, the PL of the CdSe / ZnSe _0.8 S _0.2 quantum dots was measured to be 556 nm, the half-width of the peak was 22 nm, and the average size of the electron microscope was 8.7 nm;

In step (2), the amount of ZnAc ₂ is increased to ₂ mmol, the amount of OA is increased to 8 mmol, the amount of S powder is increased to 1 mmol, dissolved in 2 ml of TBP, and the temperature of preparing the precursor solution (mixed solution F) of Zn source is 150 ° C. The synthesis temperature of the synthesized CdSe / ZnSe _0.8 S _0.2 / ZnS quantum dots is 280 ° C, and the reaction is held for 10 min. The final CdSe / ZnSe _0.8 S _0.2 / ZnS PL is 550 nm, the half-value width is 23 nm, the QY is 91.8%, and the average size of the electron microscope It is 12.0nm. Up to 83 mg of quantum dots can be dissolved in the corresponding 1 mL of printing ink.

Example 3

Preparation of CdSe / ZnSe _0.2 S _0.8 / ZnS quantum dots

The difference from Example 1 is that the CdSe core used in step (1) is UV = 538nm, OD = 50, 25nmol _{; the} amount of ZnAc ₂ is increased to 1.2mmol, the amount of Se powder is reduced to 0.1mmol, and it is dissolved in 0.2mL TOP solution ; The amount of S powder was reduced to 0.4 mmol and dissolved in 0.8 mL of TBP; the temperature of preparing a Zn source precursor solution (mixed solution C) was 200 ° C, and the temperature for synthesizing CdSe / ZnSe _0.2 S _0.8 quantum dots was 310 ° C; At 60 min, the PL of CdSe / ZnSe _0.2 S _0.8 quantum dots was measured at 534 nm, the half-width at half maximum was 22 nm, and the average size of the electron microscope was 7.6 nm;

In step (2), the amount of ZnAc _{2 was} increased to 1.5 mmol, the amount of OA was increased to 6 mmol, the amount of S powder was increased to 0.5 mmol, dissolved in 1 ml of TBP, and the temperature of preparing a precursor solution of Zn source (mixed solution F) was 200 ° C. The reaction temperature for the synthesis of CdSe / ZnSe _0.8 S _0.2 / ZnS quantum dots was 310 ° C, and the reaction was held for 60 minutes. The final PL of CdSe / ZnSe _0.2 S _0.8 / ZnS was 529 nm, the half-value width was 23 nm, and the QY was 96.7%. The size is 10.2 nm. A maximum of 156 mg of quantum dots can be dissolved in the corresponding 1 mL of printing ink.

Example 4

Preparation of CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dots

The difference from Example 1 is that the CdSe core used in step (1) has UV = 523nm, OD = 50, and 25nmol; the amount of Se powder is reduced to 0.2mmol and dissolved in 0.4mL TOP solution; the amount of S powder is increased to 0.3mmol , Dissolved in 0.6mL TBP; measured PL of CdSe / ZnSe _0.4 S _0.6 quantum dots is 526nm, half-width at 21nm, average size of electron microscope is 7.1nm;

In step (3), the amount of ZnAc _{2 was} increased to 1.2 mmol, the amount of OA was increased to 4.8 mmol, the amount of S powder was increased to 0.4 mmol, dissolved in 0.8 ml of TBP, and the final CdSe / ZnSe _0.4 S _0.6 / ZnS PL was 520 nm. The peak width was 22 nm, QY was 94.8%, and the average size of the electron microscope was 9.3 nm. A maximum of 178 mg of quantum dots can be dissolved in the corresponding 1 mL of printing ink.

Example 5

Preparation of CdSe / ZnSe / ZnS quantum dots

The difference from Example 1 is that the CdSe core used in step (1) is UV = 525nm, OD = 50, 25nmol; the amount of Se powder is 0.5mmol, dissolved in 1mL TBP solution; the reaction is held for 60min, and the CdSe / The PL of ZnSe quantum dots is 530nm, the half-width at half maximum is 20nm, and the average size of the electron microscope is 6.4nm;

In step (2), the amount of ZnAc _{2 was} increased to 1.2 mmol, the amount of OA was increased to 4.8 mmol, the amount of S powder was 1 mmol, dissolved in 2 ml of TBP, and the temperature was maintained for 60 min. The PL of CdSe / ZnSe / ZnS was 524 nm and the half-peak width It was 23 nm, QY was 93.6%, and the average size of the electron microscope was 10.8 nm. A maximum of 138 mg of quantum dots can be dissolved in the corresponding 1 mL of printing ink.

Example 6

Preparation of CdSe / ZnSe / ZnS quantum dots

The difference from Example 1 is that the amount of Se powder is 0.5 mmol, dissolved in 1 mL of TBP solution, and no S-TBP solution is added; the reaction is maintained for 60 minutes, and the PL of CdSe / ZnSe quantum dots is measured to be 501 nm and the half-width It is 24nm, the average size of the electron microscope is 5.4nm; the PL of the final CdSe / ZnSe / ZnS quantum dot is 496nm, the half-value width is 25nm, and the QY is 90.6%.

Example 7

Preparation of CdSe / ZnSe _0.2 S _0.8 / ZnS quantum dots

It differs from Example 1 only in that the amount of Se powder was reduced to 0.1 mmol and dissolved in 0.2 mL of TOP solution; the amount of S powder was reduced to 0.4 mmol and dissolved in 0.8 mL of TBP; the reaction was held for 60 min, and CdSe / ZnSe _{0.2 was} measured. The PL of the S _0.8 quantum dots is 499 nm, the half-value width is 23 nm, and the average size of the electron microscope is 5.7 nm. The PL of the CdSe / ZnSe _0.2 S _0.8 / ZnS quantum dots is 496 nm, the half-width is 23 nm, and QY is 92.4%.

Example 8 QLED based on 520nm CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dot

CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dots with a wavelength of 520 nm prepared in Example 4 were used for the preparation of QLED devices. The entire process was performed in an air atmosphere. The specific operation steps were as follows: in a glass with an ITO coating Spin-coat the PEDOT: PSS solution (BaytronPVPAl 4083, filtered through 0.45mm N66 filter paper) at 1 minute at 4000 rpm / min on the substrate, bake at 140 ° C for 10 minutes, and rotate at 2000 rpm / min within 45 seconds in order. Spin-coated PVK chlorobenzene solution, CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dots, ethanol solution of ZnO nanocrystals, and then vacuum-plated a 100 nm Ag layer, and finally sealed the device with a UV-curable resin Inside the plexiglass. The CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dot layer is about 40 nm. After testing, QLEDs based on CdSe / ZnSe _0.4 S _0.6 / ZnS quantum dots in the air process have an external quantum efficiency (EQE) of 18% and a T50 life of 100 cd · m ^-2 brightness of more than 100,000 hours.

Comparative Example 1

520nm synthesized according to the literature (K. Lee, et al., Over 40cd / A, Efficient, Green, Quantum, Dot, Electroluminescent, Device, Computing, Unique, Large-Sized, Quantum Dots, ACS Nano, 8, 4893 (2014). CdSe @ ZnS / ZnS quantum dots. The average size of CdSe @ ZnS electron microscope is 9.5nm, and the average size of CdSe @ ZnS / ZnS electron microscope is 12.7nm. Up to 43 mg of quantum dots can be dissolved in the corresponding 1 ml of printing ink.

Comparative Example 2

535nmCdSe @ synthesized according to the method of the literature (Y. Yang, et al., High-efficiency light-emitting devices based on quantum quantum dots with tailored nanostructures, Nature Photon., 9,259 (2015). ZnS quantum dots, in which the average electron microscope size of CdSe @ ZnS is 8.2nm. A maximum of 195 mg of quantum dots can be dissolved in the corresponding 1 ml of printing ink.

Comparative Example 3:

Preparation of CdSe / ZnS quantum dots

Different from Example 1, only S-TBP (0.5mmolS in 1mL TBP) was injected in step (2). The final PL of CdSe / ZnS was 526nm, the half-width of the peak was 38nm, the QY was 56.8%, and the average size of the electron microscope It is 6.8nm.

Comparative Example 4: QLED based on 520nm CdSe @ ZnS / ZnS quantum dots of Comparative Example 1

After testing, a QLED prepared in the air based on the 520nmCdSe @ ZnS / ZnS quantum dots of Comparative Example 1 (the preparation process is the same as in Example 6), and its external quantum efficiency (EQE) can reach 12%, and the brightness is 100 cd · m ^-2 The T50 life is about 1000 hours.

Comparative Example 5: QLED based on 535nm CdSe @ ZnS quantum dots of Comparative Example 2

After testing, the QLED prepared in the air based on 535nmCdSe @ ZnS / ZnS quantum dots of Comparative Example 2 has an external quantum efficiency (EQE) of 8%, and a T50 life of 100cd · m ^-2 brightness is about 8000 hours.

From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects: using the green quantum dots provided in the present application, firstly preparing CdSe quantum dots through a two-step coating method, and using this as a CdSe core A ZnSe _X S _1-X shell layer (0 <X≤1) and a ZnS shell layer are formed by coating on the periphery in order. This makes the prepared green quantum dots possess the characteristics of different absorption wavelengths of CdSe cores, and then adjusts their emission wavelengths by adjusting the reactivity and coating amount of the precursors of Se and S in the ZnSe _X S _1-X shell. In the end, green quantum dots with high optical quality (more than 90% quantum efficiency and half-peak width below 26nm) and high quantum efficiency (more than 80%) are obtained. The size of the electron microscope of the particles is between 8-12nm. Moreover, the green quantum dots obtained by the preparation method have high controllability of the emission wavelength, can realize the production scale of kilogram-level quantum dots, and have high photobleaching resistance and high air stability, which can meet the requirements for preparing devices in the air, greatly reducing The requirements and equipment cost of green QLED preparation are also discussed. The preparation method has simple and reliable operation, good controllability, is suitable for large-scale production, and has great value for the development of quantum dot applications. At the same time, QLEDs prepared using this kind of green quantum dots have ideal device lifetime (100cd · m ^-2 brightness T50 lifetime greater than 10,000 hours) and quantum efficiency (greater than 10%), meeting the needs of commercial applications.

The above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

A green quantum dot, characterized in that the green quantum dot has a CdSe / ZnSe X S 1-X / ZnS structure and includes:

CdSe core;

A ZnSe X S 1-X shell layer, covering the periphery of the CdSe core, where 0 < X ≦ 1;

A ZnS shell layer covers the periphery of the ZnSe X S 1-X shell layer.
The green quantum dot according to claim 1, wherein in the ZnSe X S 1-X shell layer, 0 <X <1.
The green quantum dot according to claim 1, wherein in the ZnSe X S 1-X shell layer, 0.2≤X≤1.
The green quantum dot according to claim 3, wherein in the ZnSe X S 1-X shell layer, 0.2 ≦ X <1.
The green quantum dot according to claim 1, wherein a particle size of the CdSe / ZnSe X S 1-X quantum dot composed of the CdSe core and the ZnSe X S 1-X shell is 5-9 nm, The particle size of the green quantum dot is 8 to 14 nm.
The green quantum dot according to claim 5, wherein the UV wavelength corresponding to the first exciton peak of the CdSe core is 495-545 nm.
The green quantum dot according to claim 6, characterized in that the emission wavelength PL of the CdSe / ZnSe X S 1-X quantum dot is 496 to 556 nm and the half-value width is 19 to 25 nm, preferably the CdSe / ZnSe The full width at half maximum of the X S 1-X quantum dots is 19 to 22 nm.
The green quantum dot according to any one of claims 1 to 7, characterized in that the light emission wavelength PL of the green quantum dot is 490 to 550 nm and the half-value width is 20 to 26 nm, preferably the green quantum dot is half. The peak width is 20 to 23 nm.
A method for preparing a green quantum dot, which comprises the following steps:

S1, preparing CdSe quantum dots as CdSe cores;

S2, forming a ZnSe X S 1-X shell layer on the periphery of the CdSe core to obtain CdSe / ZnSe X S 1-X quantum dots, where 0 < X ≦ 1;

S3. A ZnS shell layer is formed on the periphery of the CdSe / ZnSe X S 1-X quantum dot to obtain the green quantum dot according to any one of claims 1 to 6.
The method according to claim 9, wherein 0 <X <1.
The preparation method according to claim 9, wherein 0.2≤X≤1.
The method according to claim 9, wherein 0.2 ≦ X <1.
The method according to claim 9, wherein the step S2 further comprises:

S21, mixing the Zn source with the first ligand and the first organic solvent, and heating up to 150-200 ° C to obtain a mixed solution C;

S22. Mix the Se source and the 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: The mixed solution C is heated to 280-310 ° C, and then a CdSe quantum dot solution containing the CdSe quantum dots, the mixed solution D, and the mixed solution E are added thereto, and the reaction is maintained for 10 to 60 minutes to obtain containing the CdSe / ZnSe X S 1-X quantum dot CdSe / ZnSe X S 1-X quantum dot solution.
The method according to claim 13, wherein the step S3 further comprises:

S31. Mix the Zn source with the second ligand and the fourth organic solvent, and raise the temperature to 150-200 ° C to obtain a mixed solution F;

S32, mixing the S source and the fifth organic solvent to obtain a mixed solution G;

S33: The mixed solution F is heated to 280-310 ° C under the protection of an inert gas, and then the CdSe / ZnSe X S 1-X quantum dot solution and the mixed solution G are added thereto, and the temperature is maintained for 10 to 60 minutes. To obtain a green quantum dot solution containing the green quantum dot.
The method according to claim 13 or 14, wherein in the step S2, during the preparation of the ZnSe X S 1-X shell layer, Zn in the Zn source, and Zn in the Se source The molar ratio of Se to S in the S source is 1: 0.1 to 1: 0 to 0.9.
The preparation method according to claim 15, wherein in the step S3, the molar ratio of Zn in the Zn source and S in the S source during the preparation of the ZnS shell layer is 1: 0.1 to 1.
The method according to claim 16, wherein a molar ratio of the CdSe quantum dot core, the Zn in the Zn source in step S2 and the Zn in the Zn source in step S3 is 1: 1 × 10 4 to 5 × 10 5 : 1 × 10 4 to 5 × 10 5 .
A quantum dot light emitting diode, characterized by using the green quantum dot according to any one of claims 1 to 8.
The quantum dot light emitting diode according to claim 18, wherein an external quantum efficiency of the quantum dot light emitting diode is greater than 10%, and a T50 lifetime of the quantum dot light emitting diode at a brightness of 100 cd · m -2 is 10,000 hours or more.
A quantum dot composition, characterized in that the quantum dot composition comprises the green quantum dot according to any one of claims 1 to 8.