CdSe / ZnS quantum dot based on multiple binding sites and stable ligand, preparation method of CdSe / ZnS quantum dot and carrier-injection-free LED device

Abstract

The invention provides a stable-ligand CdSe / ZnS quantum dot based on multiple binding sites, a preparation method of the stable-ligand CdSe / ZnS quantum dot and a carrier-injection-free LED device. According to the scheme, the alanine modified long-chain alkylamine ligand is used, alanine endows the ligand with more sites which are mutually combined with the surfaces of the quantum dots, on one hand, more binding sites can passivate surface defects of the CdSe / ZnS quantum dots and improve the luminous efficiency, and on the other hand, the stability of the quantum dots can be improved; the prepared modified quantum dots can be applied to injection-free electroluminescent devices driven by a high-frequency alternating-current electric field.

Description

Technical Field

[0001] This invention relates to a method for preparing CdSe / ZnS quantum dots and their injection-free devices based on ligands with multiple binding sites, belonging to the field of novel nano-optoelectronic materials preparation. Background Technology

[0002] Traditional DC-driven LEDs have limitations in micro / nano displays (micrometer and nanometer displays). Injection-free LEDs (i.e., carrier-free LEDs) are light-emitting devices with insulator / QD (quantum dot) / insulator structures driven by a high-frequency AC field. Injection-free LED devices consist of an insulating layer and an emitting layer, eliminating the need for precise bandgap matching design, and have advantages in large-scale, flexible, stretchable, and micro / nano displays.

[0003] Uninjected LEDs exhibit electroluminescence driven by high-frequency, high-AC voltage. However, the high-frequency alternating electric field can easily cause ligands to detach from the quantum dot surface, leading to a decrease in device luminescence performance. Therefore, it is necessary to effectively enhance the binding of ligands to the CdSe / ZnS quantum dot surface to improve device performance and stability. Summary of the Invention

[0004] The purpose of this invention is to address the limitations of the prior art by providing a method for preparing CdSe / ZnS quantum dots with stable ligands based on multiple binding sites, as well as a method for preparing injection-free devices using the quantum dots. Modifying long-chain alkylamines with alanine yields novel amine ligands with more interaction sites on the CdSe / ZnS quantum dot surface. This enhances the binding between the ligand and the quantum dot surface. The increased number of binding sites can passivate surface defects of the CdSe / ZnS quantum dots, improving luminescence efficiency, and also increase the stability of the quantum dots. This allows the prepared modified quantum dots to be applied to injection-free electroluminescent devices driven by high-frequency AC electric fields.

[0005] This invention utilizes a hot-injection method, employing alanine-modified long-chain alkylamines as multi-binding-site ligands, to synthesize CdSe / ZnS quantum dots with good luminescence properties and stability. This method is simple, rapid, and universally applicable.

[0006] This invention provides a method for preparing CdSe / ZnS quantum dots based on ligands with multiple binding sites, the method comprising the following steps: Step 1: N-tert-butoxycarbonyl-alanine is reacted with a long-chain alkylamine in dichloromethane. The reaction product is then deprotected in trifluoroacetic acid to obtain a multi-binding-site ligand.

[0007] Step 2: Mix selenium powder with tri-n-octylphosphine and degas at 50-80°C (preferably 60°C) to obtain the first precursor solution.

[0008] Step 3: Cadmium oxide, oleic acid and solvent octadecene are heated to 180-210°C (preferably, to 210°C) under an argon atmosphere to dissolve cadmium oxide. Then, oleylamine is added and the temperature is raised to 250-270°C (preferably, to 270°C) to obtain the second precursor solution.

[0009] Step 4: Take a certain amount of the first precursor solution obtained in step 2 and inject it into the second precursor solution obtained in step 3. React for 25-35 min (preferably, 25 min), and then cool to obtain a CdSe quantum dot solution.

[0010] Step 5: Heat the CdSe quantum dots obtained in Step 4 to 160-180℃, then add zinc diethyldithiocarbamate and a multi-binding-site amine ligand, react for 10-20 min (preferably, react for 10 min), cool and purify to obtain CdSe / ZnS quantum dots with multi-binding-site ligand stability.

[0011] Furthermore, the long-chain alkylamine mentioned in step 1 is a long-chain amine with more than fourteen carbon atoms.

[0012] Furthermore, the tri-n-octylphosphine mentioned in step 2 is 2.8 to 3.0 times the amount of selenium powder.

[0013] Furthermore, the oleic acid in step 3 is 0.18 to 0.20 times the volume of the octadecene solvent.

[0014] Furthermore, the cadmium oxide mentioned in step 3 is in an amount of 0.10 to 0.12 times that of oleic acid.

[0015] Further, the oleylamine mentioned in step 3 is 0.80 to 0.90 times the volume of the octadecene solvent.

[0016] Furthermore, the volume of the first precursor liquid injected in step 4 is 0.10 to 0.12 times the volume of the second precursor liquid.

[0017] Furthermore, the amount of the multi-binding site ligand in step 5 is 2.9 to 3.1 times the amount of zinc diethyldithiocarbamate.

[0018] Furthermore, the amount of the multi-binding site ligand in step 5 is 0.06 to 0.07 times the amount of the octadecene solvent.

[0019] This invention provides a CdSe / ZnS quantum dot based on a ligand with multiple binding sites, which is prepared using the preparation method for CdSe / ZnS quantum dots based on a ligand with multiple binding sites provided in this specification.

[0020] This invention provides a carrier-injection-free LED device, comprising: an anode, an insulating layer, a quantum dot light-emitting layer, and a cathode stacked sequentially; wherein the material of the quantum dot light-emitting layer may include CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization provided in the embodiments of this specification.

[0021] Furthermore, the carrier-free LED device further includes: A first functional layer is disposed between the insulating layer and the quantum dot light-emitting layer; the first functional layer includes at least one of a hole injection layer and a hole transport layer; And / or, A second functional layer is disposed between the quantum dot light-emitting layer and the cathode; the second functional layer includes at least one of an electron injection layer and an electron transport layer.

[0022] The electron injection layer is located between the cathode and the quantum dot emitting layer; the electron transport layer is located between the electron injection layer and the quantum dot emitting layer; the hole injection layer is located between the quantum dot emitting layer and the insulating layer; and the hole transport layer is located between the quantum dot emitting layer and the hole injection layer.

[0023] Furthermore, the material of the anode may include ITO (indium tin oxide).

[0024] Furthermore, the material of the insulating layer may include PMMA, and the insulating layer is prepared by spin coating under the following conditions: concentration 50-80 mg / mL, rotation speed 3000-3500 rpm / min, duration 30-45 s, and annealing at 100-120℃ for 5-10 min.

[0025] Furthermore, the material of the hole injection layer may include PEDOT:PSS (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)), and the hole injection layer is prepared by spin coating under the following conditions: spin speed of 4000-4500 rpm / min for 40-60 s, followed by annealing at 140-150℃ for 20-30 min.

[0026] Furthermore, the material of the hole transport layer may include TFB (poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4'-(N-(sec-butylphenyl))diphenylamine)]), and the hole transport layer is prepared by spin coating under the following conditions: concentration 6-8 mg / mL, spin speed 2000-2500 rpm / min, duration 45-60 s, and annealing at 100-120℃ for 20-30 min.

[0027] Furthermore, the material of the quantum dot luminescent layer may include the quantum dots obtained in step 5. The quantum dot luminescent layer is prepared by spin coating under the following conditions: concentration 10-12 mg / mL, rotation speed 1500-2000 rpm / min, duration 45-60s, and annealing at 60-80℃ for 5-10 min.

[0028] Furthermore, the material of the electron transport layer may include TPBi (1,3,5-tris(1-phenyl-1H-benzimidazol-2-yl)benzene), and the thickness of the electron transport layer is 50-60 nm.

[0029] Furthermore, the material of the electron injection layer may include LiF, and the thickness of the electron injection layer is 1-2 nm.

[0030] Furthermore, the cathode material may include an Al thin film, and the cathode thickness is 100-120 nm.

[0031] Furthermore, the electron transport layer, electron injection layer, and anode are prepared by vacuum deposition.

[0032] The advantage of this invention lies in using alanine to modify long-chain alkylamines as multi-binding-site ligands, and employing a hot-injection method to synthesize stable CdSe / ZnS quantum dots. The multi-binding-site ligand, due to the presence of more interaction sites with the CdSe / ZnS quantum dot surface, enhances the interaction between the ligand and the CdSe / ZnS quantum dot surface, effectively passivating surface defects and improving the stability and luminescence properties of the CdSe / ZnS quantum dots. Furthermore, the entire preparation process is simple, easy to operate, and suitable for large-scale applications. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments or prior art of this specification, the drawings used in the description of the embodiments or prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 The ligand molecule synthesized in Example 1 of this invention (alanylhexadecanylamine, molecular formula: C) 19 H 40The structure and NMR spectrum of N2O (400 MHz, CDCl3): 0.88 (t, 3H), 1.25 (s, 26H), 1.33 (d, 2H), 1.49 (dd, 2H), 3.23 (dd, 2H), 3.49 (q, 1H). The molecule contains three active hydrogen atoms, which are difficult to detect in the NMR spectrum, resulting in a total of 37 hydrogen atoms. Alanine hexadecylamine is formed by the dehydration condensation of alanine and hexadecylamine. Therefore, characteristic hydrogen atoms (a and b) are selected from alanine and hexadecylamine, respectively. The hydrogen at position a is the hydrogen on the methylene group attached to the carbonyl group of alanine; the hydrogen at position b is the hydrogen on the methylene group attached to the amino group of hexadecylamine. Figure 1 The a and b positions are marked. When the ratio of hydrogen at the a position to hydrogen at the b position is 1:2, it indicates that alanine hexadecylamine has been successfully synthesized. Figure 2 The TEM image (Transmission Electron Microscope) of the CdSe / ZnS quantum dots with red light multi-binding site ligands stabilized prepared in Example 1 of the present invention shows that the present invention synthesized CdSe / ZnS quantum dots with high phase purity. Figure 3 The UV-vis (Ultraviolet-visible absorbance) spectrum of the CdSe / ZnS quantum dots with red light multi-binding site ligands prepared in Example 1 of this invention is shown. Figure 4 The PL (Photoluminescence) spectrum of the CdSe / ZnS quantum dots with red light multi-binding site ligands prepared in Example 1 of the present invention shows that the material generated in the present invention has high phase purity; Figure 5 The comparison of the stability of the CdSe / ZnS quantum dots prepared by the red light multi-binding site ligand in Example 1 of the present invention with the CdSe / ZnS quantum dots prepared by ordinary oleylamine in the comparative example under laser irradiation at 488 nm and 55 mW shows that the alanine-modified amine ligand can improve the stability of CdSe / ZnS quantum dots. Figure 6 The left image shows the structure of an injection-free light-emitting device prepared from the CdSe / ZnS quantum dots with red light-binding site ligands stabilized by Example 2 of the present invention, and its brightness under AC voltage (80 V, different frequencies) (right image). Detailed Implementation

[0035] Many specific details are set forth in the following description to provide a full understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of this application; therefore, this application is not limited to the specific embodiments disclosed below.

[0036] The present invention will be further described below with reference to specific accompanying drawings and embodiments. However, the scope of protection of the present invention is not limited to the following embodiments.

[0037] Example 1 : Step 1: Preparation of modified amine ligands.

[0038] 1-1) Dissolve 0.05-0.1 times the solvent volume of N-N-carbonyldiimidazole and 0.04-0.1 times the solvent volume of N-tert-butoxycarbonyl-alanine in 30-40 ml of dichloromethane to activate the carboxyl group of N-tert-butoxycarbonyl-alanine at room temperature, making it more readily react with long-chain amines. Then, weigh 0.03-0.08 times the solvent volume of hexadecylamine and add it to the above solution, reacting at room temperature for 12-24 h. Afterward, stop stirring and wash with saturated ammonium chloride solution. The washed solution is dried with anhydrous sodium sulfate and rotary evaporated to obtain a white solid initial product. Dry the white solid initial product for 24 h to obtain a white solid product (N-tert-butoxycarbonylpropionamide hexadecylamine).

[0039] The structural formula of N-tert-butyloxycarbonylpropionamide hexadecylamine can be as follows: .

[0040] Specifically, the reaction formula for the reaction of hexadecylamine with N-tert-butoxycarbonyl-alanine to produce N-tert-butoxycarbonylpropionamide hexadecylamine can be as follows: .

[0041] 1-2) Dissolve the product obtained in step 1-2 in 30-40 ml of dichloromethane. Add 0.05-0.1 times the volume of the solvent, using trifluoroacetic acid, dropwise in an ice-water bath. React at room temperature for 12-24 h. After the reaction is complete, rotary evaporate the solution. Then, dissolve the solution in dichloromethane and adjust the pH to 9-10. Dry with anhydrous sodium sulfate, filter, and then rotary evaporate until a white solid is obtained. Finally, dry in a vacuum oven for 24 h to obtain the modified amine ligand, namely, alanine-modified hexadecylamine.

[0042] The structural formula of alanine-modified hexadecylamine, namely alanine-6-acetylamine, can be as follows: .

[0043] Specifically, the reaction formula for obtaining alanine hexadecylamine based on N-tert-butoxycarbonylpropionamide hexadecylamine can be as follows: .

[0044] Step 2: Measure 5-6 mL of tri-n-octylphosphine, add selenium powder, and heat at 50-80 °C to obtain the first precursor solution. The amount of tri-n-octylphosphine added in Step 2 is 2.8 to 3.0 times the amount of selenium powder.

[0045] Step 3: Measure 25-30 mL of octadecene as a solvent, add 0.18-0.20 times the volume of the solvent (octadecene) of oleic acid, and add 0.10-0.12 times the amount of cadmium oxide of the oleic acid. Heat to 180-210℃ to dissolve the cadmium oxide. Then add 0.80-0.90 times the volume of the solvent (octadecene) of oleylamine, and heat to 250-270℃ to obtain the second precursor solution.

[0046] Step 4: Inject the second precursor solution obtained in step 3 into the first precursor solution obtained in step 2. The volume of the first precursor solution injected is 0.10-0.12 times the volume of the second precursor solution. React for 25-35 minutes, then cool to obtain a CdSe quantum dot solution.

[0047] Step 5: Take 8-10 mL of the CdSe quantum dot solution obtained in Step 4 and heat it to 160-180℃. Then add 0.06-0.07 times the amount of the octadecene solvent used in Step 3, along with 0.32-0.35 times the amount of the multi-binding site amine ligand (the amount of the multi-binding site ligand is 2.9-3.1 times the amount of the zinc diethyldithiocarbamate). React for 10-20 min, cool, and obtain the initial CdSe / ZnS quantum dot product.

[0048] Step 6: Add 2-3 times the volume of methyl acetate to the initial product obtained from cooling in Step 5, sonicate for 5-10 min, then centrifuge at 12500 rpm / min for 5-10 min to disperse the precipitate in toluene, and obtain red CdSe / ZnS quantum dots with multiple binding site ligands.

[0049] Example 2 : Fabrication of carrier-free injected LED devices.

[0050] The fabrication method of injection-free LED devices includes: on a glass substrate, an anode, an insulating layer, a hole injection layer, a hole transport layer, and a quantum dot light-emitting layer are sequentially prepared by spin coating, and an electron transport layer, an electron injection layer, and a cathode are sequentially prepared by vacuum deposition.

[0051] The functional layers, such as the hole injection layer, hole transport layer, electron transport layer, and electron injection layer, can be added or omitted according to actual needs. With the inclusion of functional layers such as the electron injection layer, the fabricated LED device can achieve superior luminous performance.

[0052] The anode material may include ITO; The insulating layer material may include PMMA, and the spin coating conditions for the insulating layer may be: concentration 50-80 mg / mL, rotation speed 3000-3500 rpm / min, duration 30-45 s, annealing at 100-120℃ for 5-10 min; The material of the hole injection layer may include PEDOT:PSS, and the spin coating conditions of the hole injection layer may be: a rotation speed of 4000-4500 rpm / min for 40-60 s, followed by annealing at 140-150℃ for 20-30 min. The material of the hole transport layer may include TFB, and the spin coating conditions of the hole transport layer may be: concentration 6-8 mg / mL, rotation speed 2000-2500 rpm / min, duration 45-60 s, annealing at 100-120℃ for 20-30 min; The material of the quantum dot luminescent layer may include the quantum dots obtained in step 6. The spin coating conditions of the quantum dot luminescent layer may be: concentration 10-12 mg / mL, rotation speed 1500-2000 rpm / min, duration 45-60 s, annealing at 60-80℃ for 5-10 min. The electron transport layer may be made of TPBi, and the thickness of the electron transport layer may be 50-60 nm. The electron injection layer may be made of LiF, and the thickness of the electron injection layer may be 1-2 nm. The cathode material may include an Al thin film, and the cathode thickness may be 100-120 nm.

[0053] like Figure 6 As shown, the injection-free LED device prepared based on Example 2 can achieve good light-emitting performance without relying on the injection of charge carriers without external circuitry.

[0054] Comparative Example : Step 1: Measure 5-6 mL of tri-n-octylphosphine, add selenium powder, and heat at 50-80 °C to obtain the first precursor solution. The amount of tri-n-octylphosphine added in Step 1 is 2.8 to 3.0 times the amount of selenium powder.

[0055] Step 2: Measure 25-30 mL of octadecene as a solvent, add 0.18-0.20 times the volume of the solvent (octadecene) of oleic acid, and add 0.10-0.12 times the amount of cadmium oxide of the oleic acid. Heat to 180-210℃ to dissolve the cadmium oxide. Then add 0.80-0.90 times the volume of the solvent (octadecene) of oleylamine, and heat to 250-270℃ to obtain the second precursor solution.

[0056] Step 3: Inject the second precursor solution obtained in step 2 into the first precursor solution obtained in step 1. The volume of the first precursor solution injected is 0.10-0.12 times the volume of the second precursor solution. React for 25-35 minutes, then cool to obtain a CdSe quantum dot solution.

[0057] Step 4: Take 8-10 mL of the CdSe quantum dot solution obtained in Step 3 and heat it to 160-180℃. Then add 0.06-0.07 times the amount of oleylamine as the octadecene solvent used in Step 2, and add 0.32-0.35 times the amount of zinc diethyldithiocarbamate as the oleylamine (the amount of oleylamine is 2.9-3.1 times the amount of zinc diethyldithiocarbamate). React for 10-20 min, cool, and obtain the initial CdSe / ZnS quantum dot product.

[0058] Step 5: Add 2-3 times the volume of methyl acetate to the initial product obtained from step 4 after cooling, sonicate for 5-10 min, then centrifuge at 12500 rpm / min for 5-10 min to disperse the precipitate in toluene to obtain oleylamine-stabilized red CdSe / ZnS quantum dots.

[0059] In this comparative example, except for the use of oleylamine in the step of preparing the initial CdSe / ZnS quantum dot product and the use of multi-binding-site amine ligands in Example 1, the other experimental conditions are basically the same as those in Comparative Document 1.

[0060] The above description is merely an embodiment of this application and is not intended to limit the scope of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of the claims of this application.

Claims

1. A method for preparing CdSe / ZnS quantum dots based on ligands with multiple binding sites, characterized in that, Includes the following steps: Step 1: N-tert-butoxycarbonyl-alanine and long-chain alkylamine are added to dichloromethane for reaction. The reaction product is deprotected under trifluoroacetic acid to obtain a multi-binding site ligand. Step 2: Mix selenium powder with tri-n-octylphosphine and allow it to undergo a degassing reaction to obtain the first precursor solution; Step 3: Add cadmium oxide and oleic acid to octadecene and heat under an inert gas atmosphere to dissolve the cadmium oxide; then add oleylamine and heat to obtain the second precursor solution; Step 4: Inject the first precursor solution obtained in Step 2 into the second precursor solution obtained in Step 3, and react to obtain a CdSe quantum dot solution; Step 5: After heating the CdSe quantum dot solution obtained in Step 4, add zinc diethyldithiocarbamate and the multi-binding site ligand obtained in Step 1 to react and obtain CdSe / ZnS quantum dots based on the multi-binding site ligand.

2. The method for preparing CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization according to claim 1, characterized in that, The long-chain alkylamine mentioned in step 1 is a long-chain amine with 14 or more carbon atoms.

3. The method for preparing CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization according to claim 1, characterized in that, The tri-n-octylphosphine mentioned in step 2 is 2.8 to 3.0 times the amount of selenium powder.

4. The method for preparing CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization according to claim 1, characterized in that, In step 3, the amount of oleic acid is 0.18 to 0.20 times the volume of the octadecene solvent, the amount of cadmium oxide is 0.10 to 0.12 times the amount of oleic acid by molarity, and the amount of oleylamine is 0.80 to 0.90 times the volume of the octadecene solvent.

5. The method for preparing CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization according to claim 1, characterized in that, In step 4, the volume of the first precursor liquid is 0.10 to 0.12 times the volume of the second precursor liquid.

6. The method for preparing CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization according to claim 1, characterized in that, In step 5, the amount of the multi-binding site ligand is 0.06 to 0.07 times the amount of the octadecene solvent, and the amount of zinc diethyldithiocarbamate is 0.32 to 0.35 times the amount of the multi-binding site ligand.

7. A CdSe / ZnS quantum dot based on ligands with multiple binding sites, characterized in that, The CdSe / ZnS quantum dots based on multi-binding-site ligand stabilization are prepared using the method described in any one of claims 1 to 6.

8. A carrier-injection-free LED device, characterized in that, include: An anode, an insulating layer, a quantum dot luminescent layer, and a cathode are stacked sequentially; wherein the material of the quantum dot luminescent layer includes CdSe / ZnS quantum dots based on multi-binding site ligand stabilization as described in claim 7.

9. The carrier-injection-free LED device according to claim 8, characterized in that, Also includes: A first functional layer is disposed between the insulating layer and the quantum dot light-emitting layer; the first functional layer includes at least one of a hole injection layer and a hole transport layer; And / or, A second functional layer is disposed between the quantum dot light-emitting layer and the cathode; the second functional layer includes at least one of an electron injection layer and an electron transport layer.

10. The carrier-injection-free LED device according to claim 9, characterized in that, The anode material includes indium tin oxide; Alternatively, the material of the insulating layer may include PMMA; Alternatively, the material of the hole injection layer may include PEDOT:PSS; Alternatively, the material of the hole transport layer may include TFB; Alternatively, the material of the electron transport layer may include TPBI; Alternatively, the material of the electron injection layer may include LiF; Alternatively, the cathode material may include an Al film.

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