CN111876146A

CN111876146A - Quantum dot with stable ligand, preparation method thereof and QLED (quantum light emitting diode) device

Info

Publication number: CN111876146A
Application number: CN202010908339.7A
Authority: CN
Inventors: 梁凯旋; 汪鹏生
Original assignee: Hefei Funa Technology Co ltd
Current assignee: Hefei Funa Technology Co ltd
Priority date: 2020-09-01
Filing date: 2020-09-01
Publication date: 2020-11-03

Abstract

The application relates to the field of quantum dots, in particular to a quantum dot with a stable ligand, a preparation method of the quantum dot and a QLED device. The preparation method comprises the following steps: mixing a tribenzylamine solution and a first quantum dot solution, and heating the mixed solution to 40-80 ℃ for reaction; the first quantum dot comprises a first ligand and a core-shell structure, wherein the first ligand comprises at least one of oleic acid, oleylamine or thiol. Because tribenzylamine has stronger chemical polarity and the chelating capacity with metal ions on the surface of the quantum dot is far stronger than that of conventional ligands such as oleic acid, the conventional ligands of the first quantum dot can be replaced by the tribenzylamine by mixing and reacting the tribenzylamine solution and the first quantum dot solution containing the conventional ligands. The coordinate bond formed by the tribenzylamine and the quantum dots has high strength, so that the chemical potential of Zn ions or Cd ions on the surfaces of the quantum dots is greatly improved, the Zn ions and the Cd ions are difficult to reduce and separate out, and the stability of the QLED device is improved.

Description

Quantum dot with stable ligand, preparation method thereof and QLED (quantum light emitting diode) device

Technical Field

The application relates to the field of quantum dots, in particular to a quantum dot with a stable ligand, a preparation method of the quantum dot and a QLED device.

Background

The II-VI family quantum dots mainly comprise four elements of Cd, Zn, Se and S, and the quantum dots with different structures are prepared by the reaction of precursors of the elements of Cd, Zn, Se, S and the like by a one-pot method or a two-pot method. At present, the ligand of the quantum dot is generally the same as the organic ligand of the precursor used, such as oleic acid, oleylamine and the like.

As shown in fig. 1, the strip tentacles at the periphery of the quantum dot core-shell structure are ligands coated outside the quantum dot spherical structure, and have the main functions of preventing the quantum dots from agglomerating, protecting the internal structure of the quantum dots and reducing the surface defects of the quantum dots. Quantum dots can be used in QLED devices.

The existing QLED device is generally formed by stacking thin film structures such as an electrode, a charge injection layer, a charge transmission layer, a quantum dot light emitting layer and the like, electrons and holes are injected into the quantum dot layer after electrification, so that the electrons and the holes are compositely emitted in quantum dots, the internal quantum dot efficiency of the QLED is 100%, and the External Quantum Efficiency (EQE) of the three-color QLED of red, green and blue (RGB) reaches 20% after years of development.

However, the stability of the QLED is poor at present, and the application and development of the QLED device are restricted. As shown in FIG. 2, the common QLED device structures are all positive bottom emission structures, ITO is an anode, Al is a cathode, PEDOT, PSS and TFB/Poly-TPD are respectively a hole injection layer and a hole transport layer, and a ZnO nanoparticle layer is an electron transport layer. In general, in the QLED device, since the hole injection barrier is much higher than the electron injection barrier (for example, the hole injection barrier is about 1.2eV and the electron injection barrier is only about 0.4eV in fig. 3), the electron injection rate is much higher than the hole injection rate, which easily causes electrons to accumulate at the QD/ETL interface or in the QD layer, resulting in poor stability of the QLED.

Disclosure of Invention

An object of the embodiments of the present application is to provide a quantum dot with a stable ligand, a method for preparing the quantum dot, and a QLED device, which aim to solve the problem of poor stability of the existing QLED.

In a first aspect, the present application provides a method of preparing a quantum dot with a stabilizing ligand, comprising:

mixing a tribenzylamine solution and a first quantum dot solution, and heating the mixed solution to 40-80 ℃ for reaction;

the first quantum dot comprises a first ligand and a core-shell structure, wherein the first ligand comprises at least one of oleic acid, oleylamine or thiol; the components of the core-shell structure comprise Cd, Zn, Se and S.

In another embodiment of the present application, the ratio of the amounts of the tribenzylamine and the first quantum dot is (50-100): 1.

In another embodiment of the present application, the tribenzylamine solution is prepared by mixing tribenzylamine powder with a nonpolar solution and heating at 30 to 50 ℃.

In other embodiments of the present application, the nonpolar solution is at least one selected from a normal hexane solution, a normal heptane solution, and an octadecene solution.

In another embodiment of the present application, the heating at 30 to 50 ℃ includes:

and heating the mixed solution of the tribenzylamine powder and the nonpolar solution to 30-50 ℃, and uniformly stirring until the mixed solution is clear.

In other embodiments of the present application, the step of mixing the tribenzylamine powder with the non-polar solution comprises:

the tribenzylamine powder is mixed with the nonpolar solution so that the concentration of the tribenzylamine in the mixed solution is within the range of 0.2g/ml to 0.6 g/ml.

In another embodiment of the present application, the concentration of the first quantum dot solution is 0.005 to 0.02 mmol/ml.

In other embodiments of the present application, after the mixed solution is heated to 40-80 ℃ for reaction, a polar solution is further added to precipitate the quantum dots with the stable ligands.

In a second aspect, the present application provides a quantum dot with a stabilizing ligand, where the quantum dot with a stabilizing ligand includes a second ligand and a core-shell structure, and the second ligand is tribenzylamine; the components of the core-shell structure comprise Cd, Zn, Se and S.

In a third aspect, the present application provides a QLED device comprising a quantum dot layer;

the quantum dot layer is prepared from the quantum dots prepared by the preparation method of the quantum dots with the stable ligands; or

The quantum dot layer is made of the quantum dots with the stable ligands.

The quantum dot with the stable ligand, the preparation method thereof and the QLED device provided by the embodiment of the application have the beneficial effects that:

because tribenzylamine has stronger chemical polarity, the chelating capacity of the tribenzylamine and metal ions on the surface of quantum dots is far stronger than that of conventional ligands such as oleic acid, oleylamine or mercaptan, the conventional ligands of the first quantum dots can be replaced by the tribenzylamine by mixing the tribenzylamine solution with the first quantum dot solution containing the conventional ligands such as oleic acid, oleylamine or mercaptan, heating the mixed solution to 40-80 ℃ for reaction. The coordinate bond formed by the tribenzylamine and the quantum dots has high strength, so that the chemical potential of Zn ions or Cd ions on the surfaces of the quantum dots is greatly improved, and the Zn ions and the Cd ions are difficult to reduce and separate out. However, the QLED device generally has a characteristic of excessive electron injection, so that the quantum dots are in a reduction environment when the QLED is powered on, metal ions on the surfaces of the quantum dots are easily reduced and separated out to form Zn and Cd atoms, thereby damaging the surface structures of the quantum dots and increasing the surface defects of the quantum dots. The quantum dot with stable ligand that this application embodiment provided, because Zn ion and Cd ion are difficult to reduced and are appeared out, consequently, when being applied to QLED device with it, even under the excessive environment of electron injection, the metal ion on quantum dot surface is difficult to reduce yet and is appeared out and form Zn and Cd atom to can not destroy quantum dot surface structure, thereby can improve the stability of QLED device. Furthermore, the preparation method of the quantum dot with the stable ligand provided by the embodiment of the application is simple in operation process and easy in ligand exchange, and the obtained quantum dot with the stable ligand can be suitable for quantum dot materials with different wave bands.

Drawings

In order to more clearly illustrate the technical solution of the present application, the drawings referred to below are briefly introduced.

FIG. 1 is a schematic diagram of a quantum dot core-shell structure and a ligand commonly used in the art;

FIG. 2 is a schematic diagram of a QLED device structure commonly used in the art;

fig. 3 is a schematic diagram of a hole injection barrier and an electron injection barrier of a conventional QLED device in the art.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application are clearly and completely described below, and it is obvious that the described embodiments are a part of the embodiments of the present application, but not all of the embodiments.

Thus, the detailed description of the embodiments of the present application provided below is not intended to limit the scope of the claimed application, but is merely representative of selected embodiments of the present application. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

Furthermore, the terms "first," "second," "third," and the like are used solely to distinguish one from another and are not to be construed as indicating or implying relative importance.

The embodiment of the application provides a preparation method of quantum dots with stable ligands, the quantum dots prepared by the method have stable ligands, and the quantum dots with the stable ligands are applied to a QLED device, so that the stability of the QLED device can be improved.

The preparation method of the quantum dot with the stable ligand comprises the following steps:

and step S1, preparing a first quantum dot solution.

The first quantum dot can be prepared by reacting and synthesizing precursors of elements such as Cd, Zn, Se, S and the like by a one-pot method or a two-pot method which is common in the art. Or may be purchased directly.

Further, the core-shell structure may be at least the following structure:

CdSe/ZnSe/ZnS, CdZnSe/ZnSe/ZnS, CdZnSe/ZnSe/CdZnS, CdSe/ZnSe/CdZnS, CdZnSe/ZnSe/CdZnS, CdZnS/ZnS, etc.

In some specific embodiments of the present application, the first quantum dot is prepared according to the following steps:

illustratively, precursor solutions of Cd and Zn are prepared, and the cadmium source and the zinc source are CdO, Cd (Ac)₂And Zn (Ac)₂The complexing agent is OA, ODPA, etc., the solvent is ODE (octadecylene), and the common use is Cd (OA)₂、Cd(ODPA)₂And Zn (OA)₂And the precursor solution of Se and S is prepared, and is usually TOP-Se, TOP-S and the like.

Further, nucleation: and mixing the precursor solution of Cd with the precursor solution of Se, and injecting the mixture into the precursor solution of Zn at 300 ℃ to obtain the CdZnSe nucleus.

Further, growth of ZnSe and ZnS shells: injecting TOP-Se to obtain ZnSe shell, aging for 30min after injecting Se-TOP, injecting S-TOP to grow ZnS shell, and aging for 30min to complete the growth of ZnS shell.

It should be noted that Zn (OA) is always kept in the process of quantum dot synthesis₂Excess is more than 1.2 times of the total amount of the anions of the reaction system, and the ligand of the first quantum dot obtained by cleaning after the reaction is finished is oleic acid.

Further, the first quantum dot solution is obtained by mixing the first quantum dot obtained by the preparation method with a nonpolar solution.

In some embodiments of the present application, the nonpolar solution may be at least one selected from a n-hexane solution, a n-heptane solution, and an octadecene solution.

Further, the first quantum dot and the nonpolar solution are mixed, stirred and mixed evenly at the temperature of 30-50 ℃ until the mixed solution is clear.

Further optionally, the first quantum dot and the nonpolar solution are mixed and stirred uniformly at 35-45 ℃.

Illustratively, the first quantum dot is mixed with the non-polar solution and stirred at 36 deg.C, 38 deg.C, 40 deg.C, 42 deg.C, 45 deg.C.

Furthermore, the concentration of the first quantum dot solution is 0.005-0.02 mmol/ml.

Further optionally, the concentration of the first quantum dot solution is 0.006-0.018 mmol/ml.

Further optionally, the concentration of the first quantum dot solution is 0.008-0.016 mmol/ml.

Illustratively, the concentration of the first quantum dot solution is 0.01mmol/ml, 0.012mmol/ml, 0.014mmol/ml, 0.015 mmol/ml.

And step S2, mixing the tribenzylamine solution and the first quantum dot solution.

Further, the tribenzylamine solution is prepared by mixing tribenzylamine powder with a non-polar solution and heating at 30-50 ℃.

Further optionally, the tribenzylamine solution is prepared by mixing tribenzylamine powder with a non-polar solution and heating at 35-45 ℃.

Illustratively, the tribenzylamine solution is prepared by mixing tribenzylamine powder with nonpolar solution, and heating at 36 deg.C, 38 deg.C, 40 deg.C, 42 deg.C, and 45 deg.C.

Further, the nonpolar solution is at least one selected from n-hexane solution, n-heptane solution and octadecylene solution.

Further, the step of heating at 30-50 ℃ comprises the following steps:

The mixed solution of the tribenzylamine powder and the nonpolar solution is heated to 30-50 ℃ and stirred, so that the tribenzylamine powder and the nonpolar solution can be quickly and uniformly mixed, and a clear mixed solution can be obtained more quickly.

The stirring may be performed during the entire heating process or after heating to 30 to 50 ℃.

Further, the step of mixing tribenzylamine powder with a nonpolar solution, comprising:

Further optionally, the step of mixing tribenzylamine powder with a non-polar solution, comprises:

the tribenzylamine powder is mixed with the nonpolar solution so that the concentration of the tribenzylamine in the mixed solution is within the range of 0.25g/ml to 0.55 g/ml.

the tribenzylamine powder is mixed with the nonpolar solution so that the concentration of the tribenzylamine in the mixed solution is within the range of 0.3g/ml to 0.5 g/ml.

Illustratively, the step of mixing tribenzylamine powder with a non-polar solution comprises:

the tribenzylamine powder was mixed with the nonpolar solution so that the concentration of the tribenzylamine in the mixture was in the range of 0.35g/ml, 0.36g/ml, 0.4g/ml, 0.45g/ml, 0.46g/ml, 0.48 g/ml.

In some specific embodiments of the present application, the ratio of tribenzylamine to non-polar solution is: 3 g: 6ml of the two solutions were mixed.

Illustratively, the nonpolar solution is selected from a normal hexane solution, and the proportion of the tribenzylamine to the normal hexane solution is as follows: 3 g: 6ml of the two solutions were mixed.

Further, the prepared tribenzylamine solution and the first quantum dot solution prepared in the step S1 are mixed, and the mixed solution is heated to 40-80 ℃ for reaction.

The prepared tribenzylamine solution and the first quantum dot solution prepared in the step S1 are mixed, the mixed solution is heated to 40-80 ℃ for reaction, ligand replacement can be realized, and conventional ligands such as oleic acid of the first quantum dot are replaced by the tribenzylamine. Since tribenzylamine has a polarity stronger than that of a conventional ligand such as oleic acid, when the tribenzylamine solution prepared as described above and the first quantum dot solution prepared in step S1 are mixed and reacted, tribenzylamine is more easily bound to quantum dots, thereby replacing the conventional ligand such as oleic acid.

Further optionally, the prepared tribenzylamine solution and the first quantum dot solution prepared in step S1 are mixed, and the mixed solution is heated to 45-75 ℃ for reaction.

Further optionally, the prepared tribenzylamine solution and the first quantum dot solution prepared in step S1 are mixed, and the mixed solution is heated to 50-70 ℃ for reaction.

Illustratively, the tribenzylamine solution prepared above and the first quantum dot solution prepared in step S1 are mixed, and the mixture is heated to 55 ℃, 60 ℃ or 65 ℃ to perform a reaction.

Further, the content of the tribenzylamine is larger than that of the first quantum dots by the mass amount, so that the added tribenzylamine can be ensured to be far more than the original ligand. (the content of the first quantum dot proligand is approximately 15 to 20% of the total mass of the quantum dots and the ligand).

Further, in some embodiments of the present application, the ratio of the amounts of the tribenzylamine to the first quantum dot material is (50-100): 1.

By controlling the ratio of the amounts of the tribenzylamine and the first quantum dots to (50-100): 1, the amount of the added tribenzylamine is far more than the amount of the substance of the original ligand, and the original ligand (oleic acid and the like) can be replaced more easily and effectively.

Further optionally, the ratio of the amounts of the tribenzylamine and the first quantum dot is (55-95): 1.

Further optionally, the ratio of the amounts of the tribenzylamine and the first quantum dot is (60-90): 1.

Illustratively, the ratio of the amount of material of tribenzylamine to first quantum dot is 65:1, 70:1, 75:1, 80:1, or 85: 1.

Further, after the mixed solution is heated to 40-80 ℃ for reaction, a polar solution is added to precipitate the quantum dots with the stable ligand.

Further alternatively, the polar solution is selected from ethanol and the like.

By adding a polar solution to the solution after the reaction is completed, quantum dots having a stable ligand (tribenzylamine) can be efficiently precipitated.

Further, the precipitate is centrifuged and washed, and the supernatant is removed for subsequent use.

Some embodiments of the present disclosure also provide a quantum dot with a stabilizing ligand, the quantum dot with the stabilizing ligand including a second ligand that is tribenzylamine and a core-shell structure; the components of the core-shell structure comprise Cd, Zn, Se and S. The core-shell structure is the same as that in step S1. For example, it may be: CdSe/ZnSe/ZnS, CdZnSe/ZnSe/ZnS, CdZnSe/ZnSe/CdZnS, CdSe/ZnSe/CdZnS, CdZnSe/ZnSe/CdZnS, CdZnS/ZnS, etc.

The quantum dot with the stable ligand is prepared by the preparation method of the quantum dot with the stable ligand provided by the previous embodiment.

Some embodiments of the present application also provide a QLED device comprising any of the quantum dot layers provided by embodiments of the present application.

Further, the quantum dot layer is made of the quantum dots prepared by the method for preparing quantum dots with stable ligands provided in the foregoing embodiments.

Alternatively, in some other embodiments, the QLED device includes a quantum dot layer. The quantum dot layer is made of the quantum dots with the stable ligands provided in the foregoing embodiments.

The features and properties of the present invention are further described in detail below with reference to examples:

example 1

Providing a quantum dot having a stabilizing ligand, prepared by:

(1) dissolving the synthesized first quantum dots with the ligands of oleic acid, oleylamine or mercaptan and other common ligands in a normal hexane solution, heating to 40 ℃, and uniformly stirring to obtain a clear solution, thereby obtaining a 0.01mmol/ml first quantum dot solution.

(2) Preparing a n-hexane solution of tribenzylamine, dissolving 3g of tribenzylamine powder in 6ml of the n-hexane solution, heating to 40 ℃, and uniformly stirring to obtain a clear solution.

(3) Adding 2ml of the tribenzylamine solution prepared in the step (2) into 3ml of the first quantum dot solution prepared in the step (1), heating the mixed solution to 70 ℃, and stirring for 24 hours to obtain a quantum dot solution taking the tribenzylamine as a ligand; wherein the ratio of the amounts of the tribenzylamine and the first quantum dot is 100: 1. Then adding ethanol for precipitation, centrifuging, removing supernatant, adding 3ml of n-octane into the precipitate to redissolve the quantum dots to obtain a quantum dot solution.

(4) And (4) preparing a proper amount of the quantum dot solution prepared in the step (3) into a quantum dot n-octane solution with the concentration of 0.5ml and 20mg/ml for later use.

Example 2

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: the ratio of the amounts of tribenzylamine to the first quantum dot material was 50: 1.

Example 3

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: the ratio of the amounts of tribenzylamine to the first quantum dot material was 80: 1.

Example 4

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: and (3) heating the mixed solution to 40 ℃, and stirring for 24 h.

Example 5

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: in the step (3), the mixed solution is heated to 80 ℃ and stirred for 24 h.

Example 6

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: and (3) obtaining 0.005mmol/ml of first quantum dot solution in the step (1).

Example 7

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: and (3) obtaining 0.02mmol/ml of first quantum dot solution in the step (1).

Example 8

There is provided a quantum dot having a stabilizing ligand, which is different from example 1 in that: and (2) dissolving 1.2g of tribenzylamine powder in 6ml of n-heptane solution, heating to 30 ℃, and uniformly stirring to obtain a clear solution.

Comparative example 1

A quantum dot is provided, which is the first quantum dot of which the synthesized ligand in example 1 is a common ligand such as oleic acid, oleylamine, or thiol.

Examples of the experiments

The quantum dot solution prepared in the embodiment 1-8 is used for preparing a QLED device; the preparation steps of the QLED device are as follows:

(1) spin coating PEDOT on an ITO glass substrate: PSS, the revolution number is 4000r/min, and heat treatment is carried out for 20min at 150 ℃ after the spin coating is finished.

(2) Spin coating TFB on PEDOT: and (3) performing heat treatment on the PSS layer at 140 ℃ for 20min after the rotation speed is 2000 r/min.

(3) The quantum dot solution prepared in examples 1 to 8 was spin-coated on TFB to form a quantum dot layer at 2000 r/min.

(4) And spin-coating ZnO on the quantum dot layer at 2000 r/min.

(5) And evaporating an Al electrode, and then packaging, thus completing the preparation of the QLED device.

6 samples of the quantum dots provided in examples 1 to 8 and comparative example 1 were prepared into a QLED device, and then the performance of the QLED device was examined.

The test comprises the following steps: the time (T95) during which the luminance decayed to 95% of the initial luminance, in hours; and to a lifetime at 1000nit luminance (T95 — 1 knits). Wherein, the lifetime T95-1 knits value at 1000nit brightness is obtained according to the T95 value of the corresponding sample. The specific detection steps comprise: the brightness of the device is tested by a brightness meter, and then the service life of the device is tested by an LED tester.

The results of the experiment are shown in the following table:

it can be seen from the experimental data in the above table that the quantum dot with the stable ligand prepared by the embodiment of the present application greatly improves the stability of the quantum dot due to the surface coated with the stable ligand tribenzylamine, so that the QLED device adopting the quantum dot has the advantages of strong stability, chemical inertness, good electrochemical stability and high reduction potential, the QLED device can improve the stability of the quantum dot in the electrochemical environment, and the problem of poor stability of the QLED device caused by the fact that electrons are accumulated on the QD/ETL interface or the QD layer easily caused by the QLED device in the prior art is solved. Further, as can be seen from the above table, the T95 value and the T95_1knits value of the QLED device corresponding to each quantum dot sample in comparative example 1 are significantly lower than the T95 value and the T95_1knits value of examples 1 to 8, thereby demonstrating that the quantum dots with the stabilizing ligand provided in examples 1 to 8 of the present application effectively improve the stability of the QLED device.

The above description is only a preferred embodiment of the present application and is not intended to limit the present application, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, improvement and the like made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method of preparing a quantum dot having a stabilizing ligand, comprising:

2. The method of claim 1, wherein the stable ligand of the quantum dot is selected from the group consisting of,

the content of the tribenzylamine is larger than that of the first quantum dots by mass;

optionally, the ratio of the amounts of the tribenzylamine and the first quantum dot is (50-100): 1.

3. The method for preparing quantum dots with stabilized ligands according to claim 1 or 2,

the tribenzylamine solution is prepared by mixing tribenzylamine powder with a non-polar solution and heating at 30-50 ℃.

4. The method for preparing quantum dots with stabilized ligands according to claim 3,

the nonpolar solution is selected from at least one of n-hexane solution, n-heptane solution and octadecylene solution.

5. The method for preparing quantum dots with stabilized ligands according to claim 3,

the step of heating at 30-50 ℃ comprises the following steps:

6. The method for preparing quantum dots with stabilized ligands according to claim 3,

the step of mixing tribenzylamine powder with a nonpolar solution, comprising:

7. The method of claim 1, wherein the stable ligand of the quantum dot is selected from the group consisting of,

the concentration of the first quantum dot solution is 0.005-0.02 mmol/ml.

8. The method of claim 1, wherein the stable ligand of the quantum dot is selected from the group consisting of,

and after the mixed solution is heated to 40-80 ℃ for reaction, adding a polar solution to precipitate the quantum dots with the stable ligand.

9. The quantum dot with the stabilizing ligand is characterized by comprising a second ligand and a core-shell structure, wherein the second ligand is tribenzylamine; the components of the core-shell structure comprise Cd, Zn, Se and S.

10. A QLED device comprising a quantum dot layer;

the quantum dot layer is prepared from the quantum dots prepared by the method for preparing quantum dots with stable ligands according to any one of claims 1 to 8; or

The quantum dot layer is made of the quantum dot with the stable ligand of claim 9.