Light-emitting diode of quantum dots based on ligand engineering and preparation method of light-emitting diode

Abstract

The invention discloses a light-emitting diode of quantum dots based on ligand engineering and a preparation method thereof, and the light-emitting diode comprises an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer based on ligand engineering, an electron transport layer and a cathode which are arranged from top to bottom. Wherein the quantum dot light-emitting layer is configured to obtain a quantum dot solution based on ligand engineering from a long-chain quantum dot material through a liquid phase method and a ligand exchange method. According to the light-emitting diode of the quantum dots based on ligand engineering, long-chain ligands on the surfaces of the quantum dots are replaced with halogenated benzamide ligands through a liquid-phase ligand exchange method, the light-emitting efficiency and brightness of a device are effectively improved, and the stability of the device is improved.

Description

Technical Field

[0001] The present invention relates to quantum dot materials, in particular to a light emitting diode of quantum dots based on ligand engineering and a preparation method thereof. Background Art

[0002] Quantum dots, solution-processable semiconductor nanomaterials, have attracted significant attention in the field of new display technologies due to their advantages, including high brightness, high luminous efficiency, wide color gamut, and long lifespan. Quantum dot light-emitting diodes (QLEDs), also owing to these advantages, have attracted widespread attention in areas such as lighting and high-resolution displays, demonstrating their enormous potential.

[0003] However, there is a problem of insufficient hole injection efficiency in quantum dot-based light-emitting diodes, which causes serious charge imbalance inside the device, leading to problems such as low efficiency and poor stability of the light-emitting diodes. This has greatly restricted the industrial development of quantum dot light-emitting diodes.

[0004] Currently, the solution is to use a charge transport layer with an appropriate energy level to reduce electron injection, thereby resolving the charge imbalance problem. However, this approach easily complicates the device fabrication process and also reduces device stability. Therefore, effectively addressing the carrier injection imbalance problem in devices remains a key technical challenge that needs to be addressed. Summary of the Invention

[0005] In view of the above-mentioned shortcomings of the prior art, the technical problem to be solved by the present invention is that existing quantum dot light-emitting diodes suffer from insufficient hole injection efficiency, resulting in severe charge imbalance, which in turn leads to low efficiency and poor stability. The present invention provides a quantum dot light-emitting diode based on ligand engineering. By using a liquid-phase ligand exchange method, halobenzamide ligands are used to replace the long-chain ligands on the quantum dot surface, effectively improving the device's luminous efficiency and brightness, and also enhancing its stability.

[0006] To achieve the above-mentioned objectives, the present invention provides a light-emitting diode based on ligand-engineered quantum dots, comprising an anode, a hole injection layer, a hole transport layer, a ligand-engineered quantum dot light-emitting layer, an electron transport layer and a cathode arranged from bottom to top; wherein the quantum dot light-emitting layer is configured as a long-chain quantum dot material and a ligand-engineered quantum dot solution is obtained by a liquid phase ligand exchange method.

[0007] Furthermore, the long-chain quantum dot material includes one or more of CdS, CdSe, CdTe, ZnSe, ZnSeTe, InP, and CuInS2.

[0008] Furthermore, the specific steps of the liquid phase ligand exchange method include:

[0009] Providing a synthesized quantum dot solution with long-chain ligands, and purifying the quantum dot solution to obtain a prefabricated quantum dot solution;

[0010] Providing a ligand treatment solution, the ligand treatment solution comprising a ligand material and an ethanol solvent;

[0011] Performing a ligand exchange treatment on the prefabricated quantum dot solution with a ligand material, mixing the prefabricated quantum dot solution and the ligand treatment solution at a molar ratio of 3:1, and stirring at 80° C. for 30 minutes to form a ligand quantum dot solution;

[0012] After the ligand quantum dot solution is purified and fixed to volume, it can be used as the quantum dot light-emitting layer material.

[0013] Furthermore, the ligand material is a halogenated benzamide ligand, including one or more of fluorobenzamide, chlorobenzoyl, bromobenzamide, and iodobenzamide.

[0014] Furthermore, the concentration of the ligand material is 5 mg / mL to 10 mg / mL.

[0015] Furthermore, the anode is prepared by continuously ultrasonically cleaning a glass substrate containing an ITO transparent electrode with a detergent, deionized water, acetone, and isopropyl alcohol for 15 minutes each, and then drying the glass substrate.

[0016] Furthermore, the hole injection layer was prepared by spin coating a layer of PEDOT:PSS solution on the surface of one side of the ITO transparent electrode of the cleaned glass substrate, and annealing for 30 minutes after the spin coating was completed to obtain a PEDOT:PSS film as the hole injection layer.

[0017] Furthermore, the hole transport layer was prepared by spin coating a poly[(9,9dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(p-butylphenyl))diphenylamine)] solution dissolved in chlorobenzene on the prepared PEDOT:PSS film, and annealing for 30 minutes after the spin coating was completed to obtain a TFB film as the hole transport layer.

[0018] Furthermore, the quantum dot light-emitting layer is prepared by spin-coating a ligand quantum dot solution on the prepared TFB film. The quantum dots in the quantum dot solution are a ZnSeTe / ZnSe / ZnS core-shell structure, which are dispersed in an n-octane solvent. After the spin coating is completed, annealing is performed to obtain a quantum dot light-emitting layer film as a quantum dot light-emitting layer based on ligand engineering.

[0019] Furthermore, the electron transport layer is prepared by spin coating a zinc oxide magnesium ethanol solution on the prepared ligand liquid film layer, and annealing is performed after the spin coating is completed to form a zinc oxide magnesium thin film layer as the electron transport layer.

[0020] Furthermore, the device after spin coating of the aforementioned layers is transferred to a vacuum evaporation chamber, and an Al electrode layer is evaporated on the prepared zinc magnesium oxide thin film layer as a cathode layer, thereby finally obtaining a quantum dot light emitting diode.

[0021] Technical Effects

[0022] The present invention provides a light-emitting diode based on ligand-engineered quantum dots, in which the quantum dot light-emitting layer is provided with a long-chain quantum dot material and a quantum dot solution based on ligand engineering is obtained by a liquid-phase ligand exchange method; through a simple liquid-phase ligand exchange method, the long-chain ligands of the quantum dots are replaced with short-chain ligands, effectively improving the recombination efficiency of electrons and holes, thereby enhancing the overall performance of the quantum dot light-emitting diode.

[0023] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a schematic structural diagram of a quantum dot light-emitting diode according to a preferred embodiment of the present invention;

[0025] Figure 2 1 is an electroluminescence (EL) graph of the quantum dot light-emitting diodes of Example 1 and Comparative Example 1;

[0026] Figure 3 is a current-voltage-luminance (JVL) graph of quantum dot light-emitting diodes of Example 1 and Comparative Example 1;

[0027] Figure 4 1 is a graph showing the external quantum efficiency-current density (EQE-J) of the quantum dot light-emitting diodes of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0028] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0029] In the following description, specific details, such as certain internal procedures and techniques, are provided for purposes of illustration and not limitation to facilitate a thorough understanding of the embodiments of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present invention with unnecessary detail.

[0030] like Figure 1 As shown, the present invention provides a light-emitting diode based on ligand-engineered quantum dots, comprising an anode, a hole injection layer, a hole transport layer, a ligand-engineered quantum dot light-emitting layer, an electron transport layer, and a cathode arranged from top to bottom; wherein the quantum dot light-emitting layer is configured as a long-chain quantum dot material obtained by a liquid phase ligand exchange method to obtain a ligand-engineered quantum dot solution. The long-chain quantum dot material includes one or more of CdS, CdSe, CdTe, ZnSe, ZnSeTe, InP, and CuInS2. The long-chain quantum dot material is synthesized using traditional methods, and the surface ligand is a quantum dot material selected from one or more cubic alkane compounds such as oleic acid, oleylamine, tri-n-octylphosphine, and tri-n-octylphosphine oxide.

[0031] Example 1

[0032] The quantum dot light-emitting layer is configured as a ligand quantum dot light-emitting layer. The raw material of the ligand quantum dot light-emitting layer is a long-chain quantum dot material synthesized by a traditional method, and its surface ligand is one or more cubane compounds such as oleic acid, oleylamine, tri-n-octylphosphine, and tri-n-octylphosphine oxide. By treating the long-chain quantum dot material with a liquid phase ligand exchange process, a quantum dot solution based on ligand engineering can be prepared. The preparation method of the quantum dot solution based on ligand engineering includes: 1) providing a synthesized quantum dot solution with long-chain ligands, and purifying the quantum dot solution to obtain a prefabricated quantum dot solution;

[0033] 2) providing a ligand treatment solution, wherein the ligand treatment solution comprises a halobenzamide ligand and an ethanol solvent;

[0034] 3) The concentration of the halobenzamide ligand is 5 mg / mL to 10 mg / mL;

[0035] 4) performing a ligand exchange treatment on the prefabricated quantum dot solution with a halogenated benzamide, mixing the prefabricated quantum dot solution with the ligand treatment solution at a molar ratio of 3:1, and stirring at 80° C. for 30 minutes to form a ligand quantum dot solution;

[0036] 5) After the ligand quantum dot solution is purified and fixed to volume, it can be used as the quantum dot light-emitting layer material.

[0037] In this embodiment, the method for preparing a quantum dot light-emitting device based on ligand engineering includes:

[0038] a. Preparation of anode:

[0039] The glass substrate containing the ITO transparent electrode was continuously ultrasonically cleaned with detergent, deionized water, acetone and isopropyl alcohol for 15 minutes each, and then the glass substrate was dried.

[0040] b. Preparation of hole injection layer:

[0041] A layer of poly(ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) solution was spin-coated on one side of the ITO transparent electrode of the glass substrate cleaned in step a, with the rotation speed controlled at 4000 r / min and the spin-coating time being 45 s. After the spin-coating was completed, the film was annealed at 150° C. for 30 min to obtain a PEDOT:PSS film as a hole injection layer.

[0042] c. Preparation of hole transport layer:

[0043] A poly[(9,9dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(p-butylphenyl))diphenylamine)](TFB) solution dissolved in chlorobenzene was spin-coated on the PEDOT:PSS film prepared in step b. The rotation speed was controlled at 2000 r / min and the spin-coating time was 45 s. After the spin-coating was completed, the film was annealed at 150°C for 30 min to obtain a TFB film as a hole transport layer.

[0044] d. Preparation of quantum dot light-emitting layer:

[0045] The ligand quantum dot solution was spin-coated on the TFB film prepared in step c. The quantum dots in the quantum dot solution were a ZnSeTe / ZnSe / ZnS core-shell structure and were dispersed in n-octane solvent. The quantum dot concentration was 10 mg / mL. The rotation speed was controlled at 2000 r / min and the spin coating time was 40 s. After the spin coating was completed, the film was annealed at 90° C. for 20 min to obtain a quantum dot light-emitting layer film as a quantum dot light-emitting layer based on ligand engineering.

[0046] e. Preparation of electron transport layer:

[0047] On the ligand liquid film layer prepared in step d, a zinc oxide magnesium ethanol solution was spin-coated at a speed of 4000 r / min, the solution concentration was 30 mg / mL, and the spin coating time was 40 s. After the spin coating was completed, annealing was performed at 120° C. for 20 min to form a zinc oxide magnesium thin film layer as an electron transport layer.

[0048] f. Preparation of cathode:

[0049] The spin-coated device was transferred to a vacuum evaporation chamber, and an Al electrode layer was evaporated on the zinc magnesium oxide thin film layer prepared in step e as a cathode layer with a thickness of 100 nm to finally obtain a quantum dot light-emitting diode.

[0050] Comparative Example 1

[0051] The quantum dot light-emitting layer is configured as a long-chain quantum dot light-emitting layer. The long-chain quantum dot light-emitting layer is synthesized using conventional methods, and the surface ligands are quantum dots of one or more cubane compounds such as oleic acid, oleylamine, tri-n-octylphosphine, and tri-n-octylphosphine oxide. The method for preparing a quantum dot light-emitting device includes:

[0052] a. Preparation of anode:

[0053] The glass substrate containing the ITO transparent electrode was continuously ultrasonically cleaned with detergent, deionized water, acetone and isopropyl alcohol for 15 minutes each, and then the glass substrate was dried.

[0054] b. Preparation of hole injection layer:

[0055] A layer of poly(ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS) solution was spin-coated on one side of the ITO transparent electrode of the glass substrate cleaned in step a, with the rotation speed controlled at 4000 r / min and the spin-coating time being 45 s. After the spin-coating was completed, the film was annealed at 150° C. for 30 min to obtain a PEDOT:PSS film as a hole injection layer.

[0056] c. Preparation of hole transport layer:

[0057] A poly[(9,9dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(p-butylphenyl))diphenylamine)](TFB) solution dissolved in chlorobenzene was spin-coated on the PEDOT:PSS film prepared in step b. The rotation speed was controlled at 2000 r / min and the spin-coating time was 45 s. After the spin-coating was completed, the film was annealed at 150°C for 30 min to obtain a TFB film as a hole transport layer.

[0058] d. Preparation of quantum dot light-emitting layer:

[0059] The prefabricated quantum dot solution was spin-coated on the TFB film prepared in step c. The quantum dots in the quantum dot solution were a ZnSeTe / ZnSe / ZnS core-shell structure and were dispersed in n-octane solvent. The quantum dot concentration was 10 mg / mL. The rotation speed was controlled at 2000 r / min and the spin coating time was 40 s. After the spin coating was completed, the film was annealed at 90° C. for 20 min to obtain a quantum dot light-emitting layer film as the quantum dot light-emitting layer.

[0060] e. Preparation of electron transport layer:

[0061] On the ligand liquid film layer prepared in step d, a zinc oxide magnesium ethanol solution was spin-coated at a speed of 4000 r / min, the solution concentration was 30 mg / mL, and the spin coating time was 40 s. After the spin coating was completed, annealing was performed at 120° C. for 20 min to form a zinc oxide magnesium thin film layer as an electron transport layer.

[0062] f. Preparation of cathode:

[0063] The spin-coated device was transferred to a vacuum evaporation chamber, and an Al electrode layer was evaporated on the zinc magnesium oxide thin film layer prepared in step e as a cathode layer with a thickness of 100 nm to finally obtain a quantum dot light-emitting diode.

[0064] In the above embodiment, the quantum dot light-emitting diode obtained in the above embodiment was connected to a DC power supply, and detailed technical parameters were obtained as shown in Table 2.

[0065] Table 2: Performance of quantum dot light-emitting devices in Examples and Comparative Examples

[0066]

[0067] like Figure 2-4 As shown, by comparing Example 1 with Comparative Example 1, it can be seen that the device in Example 1 exhibits a lower turn-on voltage and a higher current density. This result fully demonstrates that ligand engineering has a significant promoting effect on the improvement of the carrier transport performance of the device, and the electroluminescence intensity, efficiency and brightness of the device are significantly improved. In terms of maximum brightness and maximum external quantum efficiency, Example 1 has a significant advantage, which also shows that the light-emitting diode based on ligand engineering ZnSeTe / ZnSe / ZnS quantum dots prepared by this preparation method has the effect of improving the effective injection of charges in the light-emitting diode, thereby improving the radiative recombination efficiency of electrons and holes and improving the overall device performance of the quantum dot light-emitting diode.

[0068] The above describes in detail the preferred embodiments of the present invention. It should be understood that those skilled in the art can make numerous modifications and variations based on the concepts of the present invention without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art through logical analysis, reasoning, or limited experimentation based on the concepts of the present invention and the prior art should be within the scope of protection defined by the claims.

Claims

1. A light-emitting diode based on ligand-engineered quantum dots, characterized in that: It includes an anode, a hole injection layer, a hole transport layer, a quantum dot light-emitting layer based on ligand engineering, an electron transport layer and a cathode arranged from bottom to top; wherein, the quantum dot light-emitting layer is set as a long-chain quantum dot material and a quantum dot solution based on ligand engineering is obtained by a liquid phase ligand exchange method.

2. A light-emitting diode based on ligand-engineered quantum dots according to claim 1, characterized in that: The long-chain quantum dot material includes one or more of CdS, CdSe, CdTe, ZnSe, ZnSeTe, InP, and CuInS2.

3. A light-emitting diode based on ligand-engineered quantum dots according to claim 1, characterized in that: The specific steps of the liquid phase ligand exchange method include: Providing a synthesized quantum dot solution with long-chain ligands, and purifying the quantum dot solution to obtain a prefabricated quantum dot solution; providing a ligand treatment solution, wherein the ligand treatment solution comprises a ligand material and an ethanol solvent; performing a ligand exchange treatment on the prefabricated quantum dot solution using a ligand material, mixing the prefabricated quantum dot solution with a ligand treatment solution at a molar ratio of 3:1, and stirring at 80° C. for 30 minutes to form a ligand quantum dot solution; After the ligand quantum dot solution is purified and fixed to volume, it can be used as a quantum dot light-emitting layer material.

4. A light-emitting diode based on ligand-engineered quantum dots according to claim 3, characterized in that: The ligand material is a halogenated benzamide ligand, including one or more of fluorobenzamide, chlorobenzoyl, bromobenzamide, and iodobenzamide.

5. A light-emitting diode based on ligand-engineered quantum dots according to claim 3, characterized in that: The concentration of the ligand material is 5 mg / mL to 10 mg / mL.

6. A light-emitting diode based on ligand-engineered quantum dots according to claim 1, characterized in that: The anode is prepared by continuously ultrasonically cleaning a glass substrate containing an ITO transparent electrode with a detergent, deionized water, acetone, and isopropyl alcohol for 15 minutes each, and then drying the glass substrate.

7. A light-emitting diode based on ligand-engineered quantum dots according to claim 6, characterized in that: The hole injection layer is prepared by spin coating a layer of PEDOT:PSS solution on one side of the ITO transparent electrode of a cleaned glass substrate, and annealing for 30 minutes after the spin coating is completed to obtain a PEDOT:PSS film as the hole injection layer.

8. A light-emitting diode based on ligand-engineered quantum dots according to claim 7, characterized in that: The hole transport layer is prepared by spin coating a poly[(9,9dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(p-butylphenyl))diphenylamine)] solution dissolved in chlorobenzene on the prepared PEDOT:PSS film, and annealing for 30 minutes after the spin coating is completed to obtain a TFB film as the hole transport layer.

9. A light-emitting diode based on ligand-engineered quantum dots according to claim 8, characterized in that: The quantum dot light-emitting layer is prepared by spin-coating a ligand quantum dot solution on the prepared TFB film. The quantum dots in the quantum dot solution are a ZnSeTe / ZnSe / ZnS core-shell structure and are dispersed in an n-octane solvent. After the spin coating is completed, annealing is performed to obtain a quantum dot light-emitting layer film as a quantum dot light-emitting layer based on ligand engineering.

10. A light-emitting diode based on ligand-engineered quantum dots according to claim 9, characterized in that: The electron transport layer is prepared by spin coating a zinc oxide magnesium ethanol solution on the prepared ligand liquid film layer, and annealing is performed after the spin coating is completed to form a zinc oxide magnesium thin film layer as the electron transport layer.

11. A light-emitting diode based on ligand-engineered quantum dots according to claim 10, characterized in that: The device after spin coating of the above layers is transferred to a vacuum evaporation chamber, and an Al electrode layer is evaporated on the prepared zinc magnesium oxide thin film layer as a cathode layer, and finally a quantum dot light emitting diode is obtained.

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