A quantum dot film, a preparation method thereof, a quantum dot light emitting diode, and a display device

Abstract

The application discloses a quantum dot film and a preparation method thereof, a quantum dot light emitting diode and a display device. The preparation method comprises the following steps: providing first quantum dots, wherein the surfaces of the first quantum dots are combined with halogenated short-chain organic ligands; performing film forming treatment on the first quantum dots to form a quantum dot precursor film; and performing decomposition treatment on the quantum dot precursor film to decompose the halogenated short-chain organic ligands on the surfaces of the first quantum dots to generate halogen ions and obtain the quantum dot film; the quantum dot film comprises second quantum dots, and the surfaces of the second quantum dots are combined with the halogen ions. The halogen ions are used for modifying the quantum dots, the halogen ions can passivate defect states on the surfaces of the quantum dots, effectively improve the charge mobility of the quantum dot film, and thus improve the light emitting efficiency of the device. In addition, the quantum dot film formed is dense, which is beneficial to charge injection in the layer, promotes carrier balance in the device, and improves the service life of the device.

Description

Technical Field

[0001] This invention relates to the field of quantum dot light-emitting diodes, and more particularly to a quantum dot thin film and its preparation method, a quantum dot light-emitting diode, and a display device. Background Technology

[0002] Quantum dots typically refer to covalent compounds such as group II-IV CdSe, ZnSe, or group III-V InP, and are generally synthesized using a high-temperature hot-injection method. High temperatures of 240℃-320℃ are required for nucleation and growth during quantum dot synthesis. To control the nucleation dispersion and growth stability of quantum dots, long-chain, high-boiling-point organic ligands such as oleic acid and oleylamine are added to the precursor solution. This allows the inorganic quantum dot materials to dissolve well in organic solvents such as hexane, octane, toluene, or chlorobenzene, facilitating solution processing methods such as spin coating or printing to form quantum dot electroluminescent diodes (QLEDs), infrared-visible optoelectronic devices, and is particularly suitable for large-area display panels.

[0003] Organic ligands such as oleic acid and oleylamine enable quantum dots to be well dispersed in organic solvents. After quantum dot solution is prepared into film, the carbon chains of oleic acid and oleylamine ligands on the quantum dot surface are relatively long, usually 1.2 nm, which makes the quantum dot film not dense enough. Moreover, after film formation and heat treatment, defect states are generated, which are not conducive to the transport of electrons or holes and are not conducive to the carrier balance in QLED devices. Summary of the Invention

[0004] The inventors discovered that it is necessary to optimize the surface ligands of quantum dots by replacing long-chain organic ligands with short-chain organic ligands and to perform post-processing on the quantum dot film to improve the compactness and mobility of the film, thereby improving the carrier transport performance of the quantum dot film and the carrier balance in the QLED device, and optimizing the efficiency and lifetime of the QLED device.

[0005] The technical solution of the present invention is as follows:

[0006] A first aspect of the present invention provides a method for preparing a quantum dot thin film, comprising the steps of:

[0007] A first quantum dot is provided, wherein a halogenated short-chain organic ligand is bound to the surface of the first quantum dot;

[0008] The first quantum dot is subjected to a film-forming process to form a quantum dot precursor film;

[0009] The quantum dot precursor film is decomposed to decompose the halogenated short-chain organic ligands on the surface of the first quantum dot to generate halide ions, and the quantum dot film is obtained.

[0010] The quantum dot film includes a second quantum dot, and the surface of the second quantum dot is bonded with the halide ions.

[0011] Optionally, the first quantum dot is prepared by the following steps:

[0012] An initial quantum dot is provided, the surface of which is bound with a long-chain organic ligand;

[0013] The initial quantum dot is subjected to ligand exchange treatment using the halogenated short-chain organic ligand to obtain the first quantum dot with the halogenated short-chain organic ligand bound to its surface.

[0014] Optionally, the main chain carbon number of the halogenated short-chain organic ligand is less than 8.

[0015] Optionally, the halogenated short-chain organic ligand is selected from one or more of halogenated short-chain organic acids and halogenated short-chain organic alcohols; and / or

[0016] The halide ion is selected from one or more of fluoride ions, chloride ions, and bromide ions.

[0017] Optionally, the long-chain organic ligand is selected from one or more organic carboxylic acids with 8 or more carbon atoms and organic amines with 8 or more carbon atoms.

[0018] Optionally, the temperature of the ligand exchange treatment is 60–80°C, and the time of the ligand exchange treatment is 2–3 hours.

[0019] Optionally, the step of decomposing the quantum dot precursor film includes:

[0020] The quantum dot precursor film is subjected to ultraviolet light irradiation or plasma treatment to obtain the quantum dot film.

[0021] Optionally, when performing the ultraviolet light irradiation treatment, the power of the ultraviolet light is 500-1500W, the wavelength of the ultraviolet light is 365nm, and the ultraviolet light irradiation treatment time is 10-30min.

[0022] A quantum dot thin film, wherein the quantum dot thin film comprises quantum dots, and the surface of the quantum dots is bonded with halide ions.

[0023] A quantum dot light-emitting diode, comprising:

[0024] The quantum dot light-emitting layer is prepared by the quantum dot thin film preparation method of the present invention, or the quantum dot light-emitting layer is the quantum dot thin film of the present invention.

[0025] A display device comprising the quantum dot light-emitting diode described in this invention.

[0026] Beneficial Effects: In this invention, by converting the halogenated short-chain organic ligands on the surface of quantum dots into halide ions, i.e., transforming quantum dots with surface-bound halogenated short-chain organic ligands into quantum dots with surface-bound halide ions, a quantum dot film composed of quantum dots with surface-bound halide ions is obtained. Modifying quantum dots with halide ions can passivate all defect states on the quantum dot surface, reduce cation oxidation on the quantum dot surface, and effectively improve the charge mobility of the quantum dot film, thereby improving the luminous efficiency of the quantum dot light-emitting diode (LED). Furthermore, halide ion modification of quantum dots makes the quantum dot film formed by these quantum dots denser, which is beneficial for charge injection into the quantum dot film and promotes carrier balance in the quantum dot LED formed by the quantum dot film as the light-emitting layer, thereby improving the lifetime of the quantum dot LED. Attached Figure Description

[0027] Figure 1 This is a schematic flowchart illustrating a method for fabricating a quantum dot light-emitting diode according to an embodiment of the present invention.

[0028] Figure 2 A schematic diagram showing the formation of a first quantum dot of a surface-bound short-chain organic ligand through ligand exchange from an initial quantum dot containing a long-chain organic ligand.

[0029] Figure 3 This is a schematic diagram showing how a quantum dot precursor film composed of first quantum dots with surface-bound halogenated short-chain organic ligands is transformed into a quantum dot film composed of second quantum dots with surface-bound halide ions through UV treatment.

[0030] Figure 4 This is a schematic diagram of the structure of a quantum dot light-emitting diode provided in an embodiment of the present invention. Detailed Implementation

[0031] This invention provides a quantum dot light-emitting diode and its fabrication method. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0032] Please see Figure 1 This invention provides a method for preparing quantum dot thin films, comprising the following steps:

[0033] S1. A first quantum dot is provided, wherein a halogenated short-chain organic ligand is bound to the surface of the first quantum dot;

[0034] S2. Perform a film-forming process on the first quantum dot to form a quantum dot precursor film;

[0035] S3. The quantum dot precursor film is decomposed to decompose the halogenated short-chain organic ligands on the surface of the first quantum dot to generate halide ions, and the quantum dot film is obtained.

[0036] The quantum dot film includes a second quantum dot, and the surface of the second quantum dot is bonded with the halide ions.

[0037] In this embodiment, by converting the halogenated short-chain organic ligands on the surface of the first quantum dot into halide ions, that is, transforming the first quantum dot with surface-bound halogenated short-chain organic ligands into a second quantum dot with surface-bound halide ions, a quantum dot film composed of the second quantum dot with surface-bound halide ions is obtained. Modifying the quantum dot with halide ions can passivate all defect states on the quantum dot surface, reduce cation oxidation on the quantum dot surface, and effectively improve the charge mobility of the quantum dot film, thereby improving the luminous efficiency of the quantum dot light-emitting diode formed by the quantum dot film as the light-emitting layer. Furthermore, halide ion modification of the quantum dot makes the quantum dot film formed by the quantum dot denser, which is beneficial for charge injection into the quantum dot film and promotes carrier balance in the quantum dot light-emitting diode formed by the quantum dot film as the light-emitting layer, thereby improving the lifetime of the quantum dot light-emitting diode.

[0038] According to an embodiment of the present invention, the mobility of the quantum dot thin film prepared by the above method is increased from 10. - 2 cm 2 V -1 S -1 The order of magnitude increased to 1-20 cm 2 V -1 S -1 .

[0039] In step S1, in one embodiment, the first quantum dot is prepared by the following steps:

[0040] S11. Provide an initial quantum dot, wherein the surface of the initial quantum dot is bound with a long-chain organic ligand;

[0041] S12. The initial quantum dot is subjected to ligand exchange treatment using the halogenated short-chain organic ligand to obtain the first quantum dot with the halogenated short-chain organic ligand bound to its surface.

[0042] Typically, initial quantum dots are bound to long-chain organic ligands such as oleic acid and oleylamine on their surface, resulting in good dispersibility in organic solvents. However, after the initial quantum dot solution is deposited into a film, the relatively long carbon chains of these ligands (typically 1.2 nm) lead to insufficient density in the quantum dot film. Furthermore, after film formation and heat treatment, defect states are generated, hindering electron or hole transport. In this embodiment, ligand exchange treatment is performed on the initial quantum dots with long-chain organic ligands bound to their surface and on halogenated short-chain organic ligands to obtain the first quantum dots (e.g., those with halogenated short-chain organic ligands bound to their surface). Figure 2 As shown), a quantum dot precursor film is prepared by forming a first quantum dot with a halogenated short-chain organic ligand bound to its surface. Then, under certain conditions (such as UV treatment), the halogenated short-chain organic ligands on the surface of the first quantum dots in the quantum dot precursor film are converted into halide ions, thereby obtaining a quantum dot film composed of a second quantum dot with surface-bound halide ions (e.g., as shown). Figure 3 (As shown). In this embodiment, halogenated short-chain organic ligands are first used to modify the quantum dots. This is because halogenated short-chain organic ligands have a strong binding force with quantum dots and can increase the solubility of quantum dots, facilitating subsequent film formation. Then, the halogenated short-chain organic ligands on the surface of the first quantum dots are converted into halide ions. The halide ions can passivate all defect states on the surface of the quantum dots, reduce cation oxidation on the surface of the quantum dots, and effectively improve the charge mobility of the quantum dot film, thereby improving the luminous efficiency of the quantum dot light-emitting diode formed by the quantum dot film as the light-emitting layer. In addition, the halide ion modification of the quantum dots makes the quantum dot film formed by the quantum dots dense, which is conducive to charge injection in the quantum dot film and promotes carrier balance in the quantum dot light-emitting diode formed by the quantum dot film as the light-emitting layer, thereby improving the lifetime of the quantum dot light-emitting diode.

[0043] In step S11, in one embodiment, the long-chain organic ligand is an organic carboxylic acid with 8 or more carbon atoms or an organic amine with 8 or more carbon atoms. For example, an organic carboxylic acid with 8 or more carbon atoms is selected from one or more of octanoic acid, nonanoic acid, decanoic acid, undecyl acid, dodecyl acid, tridecyl acid, tetradecyl acid, hexadecyl acid, octadecyl acid, undecenoic acid, dodecenoic acid, tridecenoic acid, tetradecenoic acid, pentadecenoic acid, hexadecenoic acid, heptadecanoic acid, and octadecenoic acid (i.e., oleic acid, abbreviated as OA). For example, an organic amine with 8 or more carbon atoms is selected from one or more of octylamine, nonylamine, decylamine, undecylamine, dodecylamine, tridecylamine, tetradecylamine, hexadecylamine, octadecylamine, undeceneamine, dodeceneamine, trideceneamine, tetradeceneamine, pentadeceneamine, hexadeceneamine, heptadecanoamine, and octadeceneamine (i.e., oleylamine, abbreviated as OAM).

[0044] In step S12, in one embodiment, the main chain carbon number of the halogenated short-chain organic ligand is less than 8.

[0045] In one embodiment, the halogenated short-chain organic ligand is selected from one or more of halogenated short-chain organic acids and halogenated short-chain organic alcohols. For example, the halogenated short-chain organic ligand is selected from one or more of trifluoroacetic acid, trichloroacetic acid, tribromoacetic acid, trifluoroethanol, trichloroethanol, and tribromoethanol.

[0046] In one embodiment, the halide ion is selected from one or more of fluoride ions, chloride ions, and bromide ions.

[0047] In one embodiment, the ligand exchange treatment is performed at a temperature of 60-80°C.

[0048] In one embodiment, the ligand exchange treatment takes 2-3 hours.

[0049] In one embodiment, the ligand exchange treatment is performed at a temperature of 60-80°C for 2-3 hours.

[0050] In one embodiment, step S12 specifically includes: dissolving the initial quantum dots with surface-bound long-chain organic ligands in a first organic solvent, adding halogenated short-chain organic ligands, refluxing at 60-80°C for 2-3 hours, and finally centrifuging and drying to obtain the first quantum dots with surface-bound halogenated short-chain organic ligands. The first organic solvent can be 2-(trifluoromethyl)-3-ethoxydodecylfluorohexane (C9H5F... 15 O), 1-chloro-4-methoxybutane (C5H) 11 ClO), 2-bromo-1,1-diethoxyethane (C6H) 13 The first quantum dots, which are bound to halogenated short-chain organic ligands on their surface, can be dispersed in a second organic solvent such as dimethylformamide (DMF) to prepare a first quantum dot solution with a concentration of 5-30 mg / ml for subsequent film formation.

[0051] In step S2, in one embodiment, the film-forming treatment method can be a solution method (such as spin coating, printing, etc.).

[0052] In one embodiment, step S2 specifically includes: dispersing the first quantum dots in a second organic solvent such as dimethylformamide (DMF) to obtain a first quantum dot solution with a concentration of 5-30 mg / ml; and spin-coating the first quantum dot solution into a film to obtain the quantum dot precursor film. The spin-coating speed is 3000-5000 rpm.

[0053] In step S3, in one embodiment, the step of decomposing the quantum dot precursor film includes:

[0054] The quantum dot precursor film is subjected to ultraviolet (UV) irradiation or plasma (such as oxygen plasma) treatment to obtain the quantum dot film.

[0055] By subjecting the quantum dot precursor film to ultraviolet light or plasma treatment, the halogenated short-chain organic ligands on the surface of the first quantum dots can be decomposed into halide ions, thereby obtaining a quantum dot film composed of second quantum dots with surface-bound halide ions. (See...) Figure 3 As shown.

[0056] When treated with ultraviolet light, the light breaks the chemical bonds within the molecules of organic matter (such as halogenated short-chain organic ligands), achieving the direct degradation of organic matter. Ultraviolet light can directly decompose O2 to generate reactive oxygen species O(1D) and O(3P). The reactive oxygen species O(3P) further reacts with oxygen to generate ozone, and O(1D) reacts with water to generate hydroxyl radicals, thus oxidizing the organic matter. Taking CF3COOH as an example of a halogenated short-chain organic ligand, the relevant reaction equations are as follows:

[0057] CF3COOH + O2 (UV) → F - +CO2+H2O

[0058] H2O + O2 (UV) → OH·

[0059] In one embodiment, when performing the ultraviolet irradiation treatment, the power of the ultraviolet light is 500-1500W, the wavelength of the ultraviolet light is 365nm, and the duration of the ultraviolet irradiation treatment is 10-30min.

[0060] This invention provides a quantum dot thin film, wherein the quantum dot thin film comprises quantum dots, and the surface of the quantum dots is bonded with halide ions. The quantum dots can be prepared based on the quantum dot thin film preparation method described above.

[0061] In this embodiment, halide ions are used to modify quantum dots. These halide ions can passivate all defect states on the quantum dot surface, reduce cation oxidation on the quantum dot surface, and effectively improve the charge mobility of the quantum dot film, thereby improving the luminous efficiency of the quantum dot light-emitting diode. Furthermore, halide ion modification of quantum dots makes the quantum dot film formed from them denser, which is beneficial for charge injection into the quantum dot film, promotes carrier balance in the quantum dot light-emitting diode, and thus improves the lifetime of the quantum dot light-emitting diode.

[0062] In one embodiment, the halide ion is selected from one or more of fluoride ions, chloride ions, and bromide ions.

[0063] This invention provides a quantum dot light-emitting diode, comprising:

[0064] The quantum dot light-emitting layer is prepared by the quantum dot thin film preparation method described in the embodiments of the present invention, or the quantum dot light-emitting layer is the quantum dot thin film described in the embodiments of the present invention.

[0065] It should be noted that the quantum dot light-emitting diodes in this embodiment come in various forms, and are divided into upright and inverted structures. The following will mainly focus on... Figure 4 The quantum dot light-emitting diode shown is introduced below. Figure 4 As shown, the quantum dot light-emitting diode sequentially comprises a first electrode (as anode) 1, a hole injection layer 2, a hole transport layer 3, a quantum dot light-emitting layer 4, an electron transport layer 5, a second electrode (as cathode) 6, and a light extraction layer 7. The quantum dot light-emitting layer is prepared by the quantum dot thin film preparation method described in this embodiment of the invention, or the quantum dot light-emitting layer is the quantum dot thin film described in this embodiment of the invention. The preparation method of the quantum dot light-emitting diode specifically includes the following steps:

[0066] Prepare the first electrode (anode);

[0067] A hole injection layer is prepared on the first electrode;

[0068] A hole transport layer is fabricated on the hole injection layer;

[0069] The quantum dot luminescent layer is fabricated on the hole transport layer;

[0070] An electron transport layer is fabricated on the quantum dot light-emitting layer;

[0071] A second electrode (cathode) is fabricated on the electron transport layer;

[0072] A light extraction layer is prepared on the second electrode.

[0073] More detailed fabrication methods and material selection for each layer of quantum dot light-emitting diodes are existing technologies and will not be elaborated here.

[0074] This invention provides a display device, which includes the quantum dot light-emitting diode described in this invention.

[0075] The present invention will be further described below through specific embodiments.

[0076] Example 1

[0077] 1. Quantum dot surface ligand exchange:

[0078] 50 mg of surface-bound oleic acid quantum dots were dissolved in 2-(trifluoromethyl)-3-ethoxydodecylfluorohexane, 50 mg of trifluoroacetic acid was added, and the mixture was refluxed at 70 °C for 2 h. Acetone was added and the mixture was centrifuged at 7000 rpm for 10 min. After drying at 50 °C, the quantum dots were dispersed in dimethylformamide (DMF) solvent.

[0079] 2. Fabrication of quantum dot light-emitting diodes:

[0080] 21. An anode is fabricated on a transparent substrate. The anode is an ITO / Ag / ITO total reflection electrode.

[0081] 22. A PEDOT:PSS solution was spin-coated onto the anode at a speed of 4000 rpm, and then heat-treated at 150°C in air for 15 min to obtain a hole injection layer.

[0082] 23. Spin-coat a TFB solution with a concentration of 8 mg / ml onto the hole injection layer at a spin speed of 5000 rpm, and heat-treat at 150℃ under N2 for 50 min to obtain the hole transport layer.

[0083] 24. A QD solution was spin-coated onto the hole transport layer. The QD material was CdSe / CdZnSeS / ZnS, the surface ligand of the QD was trifluoroacetic acid, the QD solution concentration was 20 mg / ml, and the spin-coating speed was 3000 rpm. Then, the layer was irradiated with 365 nm, 1000 W UV light under N2 for 20 min to decompose the organic short-chain ligands, obtaining a dense quantum dot film with F ion-modified Cd or Zn cations on the quantum dot surface. This effectively improves the mobility of the quantum dot film, from 10... -2 The size has increased to 1-20cm 2 V -1 S -1 ;

[0084] 25. A ZnMgO nanocrystal solution was spin-coated onto the quantum dot luminescent layer, wherein the mass content of Mg was 10% and the concentration of ZnMgO nanocrystal solution was 30 mg / ml, and the spin-coating speed was 4000 rpm; then, it was heat-treated at 90℃ for 20 min to obtain an electron transport layer.

[0085] 26. A cathode was fabricated on the electron transport layer using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The cathode material was Ag and the thickness was 20 nm.

[0086] 27. A CPL layer (light extraction layer) is prepared on the cathode using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The CPL material is NPB with a thickness of 80 nm.

[0087] Example 2

[0088] 1. Quantum dot surface ligand exchange:

[0089] 50 mg of surface-bound oleylamine quantum dots were dissolved in 1-chloro-4-methoxybutane, 50 mg of trichloroacetic acid was added, and the mixture was refluxed at 60 °C for 3 h. Acetone was added and the mixture was centrifuged at 3000 rpm for 10 min. After drying at 50 °C, the quantum dots were dispersed in dimethylformamide (DMF) solvent.

[0090] 2. Fabrication of quantum dot light-emitting diodes:

[0091] 21. An anode is fabricated on a transparent substrate. The anode is an ITO / Ag / ITO total reflection electrode.

[0092] 22. A PEDOT:PSS solution was spin-coated onto the anode at a speed of 4000 rpm, and then heat-treated at 150°C in air for 15 min to obtain a hole injection layer.

[0093] 23. Spin-coat a TFB solution with a concentration of 6 mg / ml onto the hole injection layer at a spin speed of 4000 rpm, and heat-treat at 150℃ under N2 for 60 min to obtain the hole transport layer.

[0094] 24. A QD solution was spin-coated onto the hole transport layer. The QD material was InP / ZnSe / ZnS, the surface ligand of the QD was trichloroacetic acid, the QD solution concentration was 30 mg / ml, and the spin-coating speed was 4000 rpm. Then, the layer was irradiated with 365 nm, 800 W UV light under N2 for 10 min to decompose the organic short-chain ligands, obtaining a dense quantum dot film with Cl ions modified to Cd or Zn cations on the quantum dot surface. This effectively improves the mobility of the quantum dot film, from 10... -2 The size has increased to 1-20cm 2 V -1 S -1 ;

[0095] 25. A ZnMgO nanocrystal solution was spin-coated onto the quantum dot luminescent layer, wherein the mass content of Mg was 10% and the concentration of ZnMgO nanocrystal solution was 20 mg / ml, and the spin-coating speed was 3000 rpm; then, it was heat-treated at 90℃ for 20 min to obtain an electron transport layer.

[0096] 26. A cathode was fabricated on the electron transport layer using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The cathode material was Ag and the thickness was 25 nm.

[0097] 27. A CPL layer (photoextraction layer) is prepared on the cathode using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The CPL material is NPB with a thickness of 50 nm.

[0098] Example 3

[0099] 1. Quantum dot surface ligand exchange:

[0100] 50 mg of surface-bound oleic acid quantum dots were dissolved in 2-bromo-1,1-diethoxyethane, 50 mg of tribromoethanol was added, and the mixture was refluxed at 60 °C for 2.5 h. Acetone was added, and the mixture was centrifuged at 10,000 rpm for 10 min. After drying at 80 °C, the quantum dots were dispersed in dimethylformamide (DMF) solvent.

[0101] 2. Fabrication of quantum dot light-emitting diodes:

[0102] 21. An anode is fabricated on a transparent substrate. The anode is an ITO / Ag / ITO total reflection electrode.

[0103] 22. A PEDOT:PSS solution was spin-coated onto the anode at a speed of 4000 rpm, and then heat-treated at 150°C in air for 15 min to obtain a hole injection layer.

[0104] 23. Spin-coat a TFB solution with a concentration of 8 mg / ml onto the hole injection layer at a spin speed of 5000 rpm, and heat-treat at 150℃ under N2 for 50 min to obtain the hole transport layer.

[0105] 24. A QD solution was spin-coated onto the hole transport layer. The QD material was CdSe / CdZnSeS / ZnS, the surface ligand of the QD was tribromoethanol, the QD solution concentration was 20 mg / ml, and the spin-coating speed was 3000 rpm. Then, the layer was irradiated with 365 nm, 1000 W UV light under N2 for 20 min to decompose the organic short-chain ligands, obtaining a dense quantum dot film with Br ion-modified Cd or Zn cations on the quantum dot surface. This effectively improves the mobility of the quantum dot film, from 10... -2 The size has increased to 1-20cm 2 V -1 S -1 ;

[0106] 25. A ZnMgO nanocrystal solution was spin-coated onto the quantum dot luminescent layer, wherein the mass content of Mg was 10% and the concentration of ZnMgO nanocrystal solution was 30 mg / ml, and the spin-coating speed was 4000 rpm; then, it was heat-treated at 90℃ for 20 min to obtain an electron transport layer.

[0107] 26. A cathode was fabricated on the electron transport layer using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The cathode material was Ag and the thickness was 20 nm.

[0108] 27. A CPL layer (light extraction layer) is prepared on the cathode using a vacuum evaporation process with a deposition rate of 1-5 angstroms per second. The CPL material is NPB with a thickness of 80 nm.

[0109] Comparative Example 1

[0110] It is basically the same as Example 1, except that:

[0111] The quantum dot luminescent layer was prepared by spin-coating a QD solution onto the hole transport layer. The QD material was CdSe / CdZnSeS / ZnS, the surface ligand of the QD was oleic acid, the concentration of the QD solution was 20 mg / ml, the spin-coating speed was 3000 rpm, and the layer was heat-treated at 90℃ for 55 min under N2.

[0112] The quantum dot light-emitting diodes prepared in Examples 1-3 and Comparative Example 1 were subjected to performance tests, and the test results are shown in Table 1 below:

[0113] Table 1

[0114] EQE T50@1000nit Example 1 13％ 1200h Example 2 12％ 1000h Example 3 15％ 1500h Comparative Example 1 10％ 200h

[0115] As can be seen from Table 1 above, the external quantum efficiency and lifetime of the quantum dot light-emitting diodes provided in Examples 1-3 are significantly higher than those of the quantum dot light-emitting diode in Comparative Example 1, indicating that the quantum dot light-emitting diodes obtained in the examples have better luminous efficiency and longer lifetime.

[0116] It should be understood that the application of the present invention is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for preparing a quantum dot thin film, characterized in that, Including the following steps: A first quantum dot is provided, wherein a halogenated short-chain organic ligand is bound to the surface of the first quantum dot; The first quantum dot is subjected to a film-forming process to form a quantum dot precursor film; The quantum dot precursor film is decomposed to decompose the halogenated short-chain organic ligands on the surface of the first quantum dot to generate halide ions, and the quantum dot film is obtained. The quantum dot film includes a second quantum dot, and the surface of the second quantum dot is bound with the halide ions; The halogenated short-chain organic ligand has less than 8 carbon atoms in its main chain; The halogenated short-chain organic ligand is selected from one or more of halogenated short-chain organic acids and halogenated short-chain organic alcohols; The step of decomposing the quantum dot precursor film includes: subjecting the quantum dot precursor film to ultraviolet light irradiation treatment.

2. The method for preparing quantum dot thin films according to claim 1, characterized in that, The first quantum dot was prepared by the following steps: An initial quantum dot is provided, the surface of which is bound with a long-chain organic ligand; The initial quantum dot is subjected to ligand exchange treatment using the halogenated short-chain organic ligand to obtain the first quantum dot with the halogenated short-chain organic ligand bound to its surface.

3. The method for preparing quantum dot thin films according to claim 1, characterized in that, The halide ion is selected from one or more of fluoride ions, chloride ions, and bromide ions.

4. The method for preparing quantum dot thin films according to claim 2, characterized in that, The long-chain organic ligand is selected from one or more organic carboxylic acids with 8 or more carbon atoms and organic amines with 8 or more carbon atoms.

5. The method for preparing quantum dot thin films according to claim 2, characterized in that, The ligand exchange treatment is performed at a temperature of 60-80°C for 2-3 hours.

6. The method for preparing quantum dot thin films according to claim 1, characterized in that, The steps for decomposing the quantum dot precursor film include: The quantum dot precursor film is subjected to ultraviolet light irradiation or plasma treatment to obtain the quantum dot film.

7. The method for preparing quantum dot thin films according to claim 6, characterized in that, When performing the ultraviolet light irradiation treatment, the power of the ultraviolet light is 500~1500W, the wavelength of the ultraviolet light is 365nm, and the ultraviolet light irradiation treatment time is 10~30min.

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