Preparation method of multi-interface coupled indium phosphide quantum dots and electroluminescent diode

Abstract

The application relates to a preparation method of a multi-interface coupling indium phosphide quantum dot and an electroluminescent diode, and belongs to the field of semiconductor light emission, display and nanotechnology. In the application, tri (dimethylamino) phosphine is reacted with an indium halide oleylamine solvent at 160 DEG C to 200 DEG C to generate an indium phosphide nanocrystal core, then the temperature is increased to 300 DEG C to 350 DEG C, zinc oleate, tri-n-octylphosphine-selenium and tri-n-octylphosphine-sulfur are gradually injected, and a polar solvent and a crosslinking agent are injected; 3-5 quantum dots are high-temperature fused through interfaces to realize interface coupling, and a multi-interface coupling core-shell indium phosphide / zinc selenide / zinc sulfide quantum dot is obtained. The quantum dot has a unique coupling structure, can effectively inhibit photo-generated exciton Auger recombination, improve the charge transport performance of a quantum dot film, has higher stability and a higher fluorescence quantum yield, and can be used for preparing a high-efficiency electroluminescent diode with high tube efficiency and good working stability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of nanotechnology and light-emitting display, and particularly relates to a preparation method of a multi-interface coupling indium phosphide quantum dot and electroluminescent diode, and belongs to the field of semiconductor light-emitting, display and nanotechnology. BACKGROUND

[0002] Quantum dots are semiconductor nanocrystals with quantum confinement effect. Since discovered in the 1980s, quantum dots have attracted much attention from the scientific and industrial communities due to their excellent photoluminescence performance and unique band gap tunability. Currently, quantum dots have been widely applied in the fields of display, lighting and biological fluorescent labeling. Quantum dots have s-electron level and p-electron level atomic-like properties, and exhibit quantum strong confinement, which are called "artificial atoms".

[0003] The synthesis technology of II-VI quantum dots represented by CdSe is relatively mature. However, II-VI quantum dots usually contain highly toxic elements such as cadmium or lead, which not only have great harm to human body, but also cause environmental and ecological problems. Therefore, the design and research of low-toxicity and high-performance quantum dot materials are the focus of attention. III-V quantum dots represented by indium phosphide (InP) have lower toxicity, and through controlling the particle size of quantum dots, the spectral range can basically cover the entire visible light region, and even reach the near-infrared region. Therefore, InP quantum dots, as one of the best alternatives to CdSe quantum dots, have broad prospects in the field of light-emitting display.

[0004] The synthesis of III-V quantum dots is difficult, and the optical performance is low. Mainly reflected in the size dispersion of III-V quantum dots is large, the absorption peak characteristic peak is not obvious, the crystalline quality is poor and the solvent dispersibility is not good, etc. In 1994, Nozik et al. (Journal of Physical Chemistry, 1994, 98(19): 4966-4969) used InCl3oxalate complex and tris (trimethylsilyl) phosphine (P (Si (CH3) 3) 3) in trioctylphosphine oxide solvent to synthesize InP quantum dots (size dispersion 20%), which greatly promoted the development of III-V quantum dot synthesis technology represented by InP. In 2001, Peng et al. (Nano Letters, 2002, 2(9): 1027-1030) reported the use of indium acetate and various chain length long-chain fatty acids (such as tetradecanoic acid, hexadecanoic acid, etc.) to react with organic phosphorus source in non-coordinating solvent octadecene (ODE) to synthesize InP quantum dots. The fluorescence quantum yield of InP quantum dots coated with ZnS or ZnSe shell is improved to 40%. The current mature silicon-based phosphorus synthesis system is based on this and is constantly optimized and developed. However, this system has problems such as expensive phosphorus source, strong reaction activity, flammable and explosive, carboxylic acid ligand oxidizing quantum dot surface, etc. In 2015, Tessier et al. (Chemistry of Materials, 2015, 27(13): 4893-4898) reacted amino phosphine with a series of indium halides. Benefiting from the joint action of amine and halide, tunable InP quantum dots with emission wavelength of 550-630 nm were prepared. This system uses amino phosphine as phosphorus source, which has the advantages of low cost and green safety, and uses oleylamine as ligand, which avoids the problem of carboxylic acid oxidizing quantum dot surface. However, the optical performance of InP quantum dots synthesized by this method is poor.

[0005] Due to the covalent bonding and oxidizable nature of InP quantum dots, it has been a challenge to apply InP quantum dots in light-emitting diodes (LEDs). In 2019, Peng et al. (J. Am. Chem. Soc, 2019, 141, 6448-6452) coated InP quantum dots with a ZnSe molecular layer, which alleviated the surface oxidation of the quantum dots. By a unique cleaning method, the excess indium carboxylate ligands on the surface of the quantum dots were removed, which solved the problem of In element penetration into the shell layer, and synthesized InP / ZnSe / ZnS quantum dots with a stoichiometrically balanced composition. The quantum dots were prepared into an electroluminescent LED, and the external quantum efficiency reached 14.2%. In the same year, Won et al. (Nature, 2019, 575, 634-638) removed the oxidation layer on the surface of the quantum dots by using a hydrofluoric acid etching method. By growing the shell layer at a high temperature, high-quality InP / ZnSe / ZnS quantum dots were synthesized, and an electroluminescent diode was prepared. However, the synthesis of the InP quantum dots has problems such as complex process, flammable and explosive raw materials, and high cost. SUMMARY

[0006] In view of the problems of difficult synthesis, high cost, flammable and explosive raw materials, and complex process flow of high-quality InP quantum dots, the present application designs a preparation method of multi-interface coupled InP quantum dots and electroluminescent diodes. A method for one-step continuous synthesis of multi-interface coupled InP / ZnSe / ZnS quantum dots with a core-shell structure is designed, which is conducive to large-scale production. The unique coupling structure significantly reduces surface defects, achieves higher fluorescence quantum yield, and further obtains an electroluminescent LED with high external quantum efficiency and good stability.

[0007] The present application is realized by the following technical scheme: a preparation method of multi-interface coupled InP quantum dots, one-step continuous synthesis of multi-interface coupled InP / ZnSe / ZnS quantum dots with a core-shell structure, specifically including the following steps:

[0008] (1) halogenated indium and oleylamine are placed in a flask and heated, stirred, and vacuumed to obtain an indium source solution with a concentration of 0.07-0.12 moles, and the temperature is raised to 160-200°C, and a tris(dimethylamino) phosphine solution is quickly injected, and the molar ratio of phosphorus to indium is 3:1-5:1, and the temperature is maintained for 20-40 minutes;

[0009] (2) the temperature is raised to 300-350°C, 0.3-0.5 moles of zinc oleate and 1-2 moles of tri-n-octylphosphine-selenium are mixed and injected into the reaction system, and the temperature is maintained for 40-80 minutes, and then 1-2 moles of tri-n-octylphosphine-sulfur is injected, and the temperature is maintained for 20-40 minutes;

[0010] (3) increasing temperature to 340-360℃, injecting 0.5-1.5 moles of polar solvent and 3-5 ml of cross-linking agent, and keeping for 15-30 minutes;

[0011] (4) decreasing temperature to 220-260℃, injecting 1-2 moles of zinc oleate and tri-n-octylphosphine-sulfur, keeping for 15-30 minutes, and stopping the reaction;

[0012] (5) adding ethanol or acetone, centrifuging the reaction solution, repeatedly centrifuging with n-hexane and ethanol, and then dissolving into an organic solvent to obtain a multi-interface coupled indium phosphide quantum dot solution. The polar solvent is glycerol and / or ethylene glycol, and the cross-linking agent is tetra(3-mercaptopropionic acid) pentaerythritol ester and / or tetra(2-mercaptoacetic acid) pentaerythritol ester.

[0013] The indium halide is indium chloride, indium bromide or indium iodide.

[0014] The organic solvent is n-octane, toluene or dichloromethane.

[0015] A multi-interface coupled indium phosphide quantum dot electroluminescent diode, which uses the multi-interface coupled indium phosphide quantum dot solution prepared above to prepare a light-emitting layer.

[0016] A preparation method of a multi-interface coupled indium phosphide quantum dot electroluminescent diode, the preparation steps being as follows:

[0017] (1) printing a hole injection material on a transparent conductive substrate to form a 50-70 nm thick hole injection layer, and then printing a hole transport material on the hole injection layer to form a 30-50 nm thick hole transport layer, and annealing at 100-150℃ for 10-30 minutes;

[0018] (2) depositing the multi-interface coupled indium phosphide quantum dot solution on the hole transport layer to form a 20-50 nm thick multi-interface coupled indium phosphide quantum dot light-emitting layer, and annealing at 50-80℃ for 20-40 minutes;

[0019] (3) printing a 0.5-1.5 molar concentration zinc oxide or magnesium-doped zinc oxide ethanol solution on the quantum dot layer to form a 30-50 nm thick electron transport layer, and annealing at 40-80℃ for 20-40 minutes;

[0020] (4) depositing a metal cathode material on the electron transport layer by vacuum evaporation to form a 70-100 nm thick electrode, and obtaining an electroluminescent diode.

[0021] The hole injection material is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid); the hole transport layer material is one of 1,2,4,5-tetrakis(trifluoromethyl)benzene, poly(9-vinylcarbazole), and poly[bis(4-phenyl)(4-butylphenyl)amine].

[0022] The transparent conductive substrate is one of indium-doped tin oxide or silver nanowires; the metal cathode material is one of aluminum, silver, and gold.

[0023] The beneficial effects of the present application are:

[0024] (1) One-step continuous synthesis of multi-interface coupled core-shell structure indium phosphide / zinc selenide / zinc sulfide quantum dots, compared with the traditional synthesis method, the reagents used are more economical and safe, the synthesis process is simple, and it is conducive to large-scale production.

[0025] (2) 3-5 quantum dots are coupled by interface high-temperature welding to obtain multi-interface coupled core-shell indium phosphide / zinc selenide / zinc sulfide quantum dots. The unique coupling structure significantly reduces surface defects and achieves higher fluorescence quantum yield.

[0026] (3) Multi-interface coupled indium phosphide quantum dot light-emitting diodes have high current efficiency and external quantum efficiency (efficiency up to 24%), good working stability, and long service life, meeting the requirements of actual use conditions. Therefore, the present application is an important breakthrough in the field of non-heavy metal quantum dot lighting, and has broad application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is an electron micrograph of multi-interface coupled indium phosphide quantum dots;

[0028] Figure 2 is an electron micrograph of the cross section of a multi-interface coupled indium phosphide quantum dot electroluminescent diode, (1) is a transparent conductive substrate, (2) is a hole transport layer material, (3) is a multi-interface coupled indium phosphide quantum dot light-emitting layer, (4) is an electron transport layer material, and (5) is a metal cathode.

[0029] Figure 3 is the external quantum efficiency curve of the electroluminescent diode. DETAILED DESCRIPTION

[0030] In order to make the purpose, technical solutions and advantages of the present application clearer and more apparent, the present application will be further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0031] In contrast, the present application encompasses any alternatives, modifications, equivalent methods and solutions made within the spirit and scope of the present application as defined by the claims. Further, in order to give the public a better understanding of the present application, some specific details are described in the following detailed description of the present application. The present application can also be fully understood without these specific details.

[0032] Example 1

[0033] Indium chloride and oleylamine were mixed in a molar ratio of 1:15, placed in a container of a heating device, stirred, vacuumed, and heated to 120°C to obtain an indium precursor solution with a concentration of 0.12 moles; tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed in a molar ratio of 1:3 to obtain a phosphine precursor solution with a concentration of 3.6 moles; under inert gas protection, 10 milliliters of the indium precursor solution was heated to 200°C, 4.5 millimoles of the phosphine precursor solution was injected, and the temperature was maintained for 40 minutes. The temperature was increased to 350°C, 16 milliliters of zinc oleate with a concentration of 0.5 moles and 3 milliliters of tri-n-octylphosphine-selenium with a concentration of 2 moles were mixed and then injected into the reaction system, the temperature was maintained for 80 minutes, 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles was then injected, and the temperature was maintained for 40 minutes. The temperature was increased to 360°C, 1.5 millimoles of pentaerythritol tetra(3-mercaptopropionate) and 5 milliliters of glycerol were injected, and the temperature was maintained for 30 minutes. The temperature was decreased to 260°C, 4 milliliters of zinc oleate with a concentration of 0.5 moles and 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles were injected, and the temperature was maintained for 30 minutes. The reaction solution was cooled to 30°C using a cold air gun, and the reaction was stopped. Ethanol was added, the reaction solution was centrifuged, and then repeated 5 times using n-hexane and ethanol for centrifugation, and then dissolved in n-octane to obtain a multi-interface coupled indium phosphide quantum dot solution with a concentration of 0.5 moles, which was used for subsequent preparation of light-emitting diodes.

[0034] A 50-nanometer-thick hole injection layer was printed on a transparent conductive substrate using 0.5-molar-concentration poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), followed by printing a 30-nanometer-thick hole transport layer on the hole injection layer using 0.5-molar-concentration 1,2,4,5-tetra(trifluoromethyl)benzene, and annealing at 100°C for 10 minutes. A 20-nanometer-thick quantum dot light-emitting layer was obtained by depositing a 0.5-molar-concentration multi-interface coupled indium phosphide quantum dot solution on the hole transport layer and annealing at 30°C for 50 minutes. A 30-nanometer-thick electron transport layer was obtained by depositing a 0.5-molar-concentration magnesium-doped zinc oxide electron transport material on the multi-interface coupled indium phosphide quantum dot light-emitting layer and annealing at 40°C for 20 minutes. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0035] Table 1 Quantum dots and their electroluminescent LED performance

[0036]

[0037] Example 2

[0038] Indium bromide and oleylamine were mixed in a molar ratio of 1:20, placed in a container of a heating device, stirred, vacuumed, and heated to 120°C to obtain an indium precursor solution with a concentration of 0.09 moles; tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed in a molar ratio of 1:3 to obtain a phosphine precursor solution with a concentration of 3.6 moles; under inert gas protection, 10 milliliters of the indium precursor solution was heated to 180°C, 3.6 millimoles of the phosphine precursor solution was injected, and the temperature was maintained for 30 minutes. The temperature was increased to 325°C, 16 milliliters of zinc oleate with a concentration of 0.4 moles and 3 milliliters of tri-n-octylphosphine-selenium with a concentration of 1.5 moles were mixed and then injected into the reaction system, and the temperature was maintained for 60 minutes. Then, 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles was injected, and the temperature was maintained for 30 minutes. The temperature was increased to 350°C, 1 millimole of pentaerythritol tetra(3-mercaptopropionate) and 4 milliliters of glycerol were injected, and the temperature was maintained for 20 minutes. The temperature was decreased to 240°C, 4 milliliters of zinc oleate with a concentration of 0.4 moles and 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 1.5 moles were injected, and the temperature was maintained for 20 minutes. The reaction solution was cooled to 30°C using a cold air gun, and the reaction was stopped. Ethanol or acetone was added, the reaction solution was centrifuged, and then hexane and ethanol were repeatedly centrifuged four times. Then, the solution was dissolved in n-octane to obtain a multi-interface coupled indium phosphide quantum dot solution with a concentration of 1 mole, which was used for subsequent preparation of light-emitting diodes.

[0039] Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) with a concentration of 0.5 moles was printed on a transparent conductive substrate to form a 60-nanometer-thick hole injection layer, and then 1,2,4,5-tetra(trifluoromethyl)benzene with a concentration of 0.5 moles was printed on the hole injection layer to form a 40-nanometer-thick hole transport layer, which was annealed at 120°C for 20 minutes. A quantum dot light-emitting layer with a thickness of 40 nanometers was obtained by depositing a multi-interface coupled indium phosphide quantum dot solution with a concentration of 1 mole on the hole transport layer and annealing at 60°C for 20 minutes. A 40-nanometer-thick electron transport layer was obtained by depositing magnesium-doped zinc oxide electron transport material with a concentration of 0.5 moles on the multi-interface coupled indium phosphide quantum dot light-emitting layer and annealing at 60°C for 30 minutes. An 80-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0040] Table 2 Quantum dots and their electroluminescent LED performance

[0041]

[0042] Example 3

[0043] Indium iodide and oleylamine were mixed in a molar ratio of 1:25, placed in a container of a heating device, stirred, vacuumed, and heated to 120°C to obtain an indium precursor solution with a concentration of 0.07 moles; tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed in a molar ratio of 1:3 to obtain a phosphine precursor solution with a concentration of 3.6 moles; under inert gas protection, 10 milliliters of the indium precursor solution was heated to 160°C, 2.7 moles of the phosphine precursor solution was injected, and the solution was incubated for 20 minutes. The temperature was raised to 300°C, 16 milliliters of zinc oleate with a concentration of 0.3 moles and 3 milliliters of tri-n-octylphosphine-selenium with a concentration of 1 mole were mixed and then injected into the reaction system, and the solution was incubated for 40 minutes. Then, 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 1 mole was injected, and the solution was incubated for 20 minutes. The temperature was raised to 340°C, 3 milliliters of ethylene glycol and 0.5 millimoles of pentaerythritol tetra(2-mercaptoacetate) were injected, and the solution was incubated for 15 minutes. The temperature was lowered to 220°C, 4 milliliters of zinc oleate with a concentration of 0.3 moles and 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 1 mole were injected, and the solution was incubated for 15 minutes. The reaction solution was cooled to 30°C by using a cold air gun, and the reaction was stopped. Ethanol or acetone was added, the reaction solution was centrifuged, and then hexane and ethanol were used for repeated centrifugation for three times. Then, the solution was dissolved in n-octane to obtain a multi-interface coupled indium phosphide quantum dot solution with a concentration of 1.5 moles, which was used for the preparation of subsequent light-emitting diodes.

[0044] Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) with a concentration of 0.5 moles was printed on a transparent conductive substrate to form a 70-nanometer-thick hole injection layer, and then poly(9-vinylcarbazole) with a concentration of 0.5 moles was printed layer by layer on the transparent conductive substrate to form a 50-nanometer-thick hole transport layer, which was annealed at 150°C for 30 minutes. A multi-interface coupled indium phosphide quantum dot solution with a concentration of 1.5 moles was deposited on the hole transport layer and annealed at 80°C for 40 minutes to obtain a 50-nanometer-thick quantum dot light-emitting layer. An electron transport material of magnesium-doped zinc oxide with a concentration of 1.5 moles was deposited on the multi-interface coupled indium phosphide quantum dot light-emitting layer and annealed at 80°C for 40 minutes to obtain a 50-nanometer-thick electron transport layer. A 100-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0045] Table 3 Quantum dots and their electroluminescent LED performance

[0046]

[0047] Summary

[0048] In Examples 1-3, the types and concentrations of precursors and the temperature and time of the reaction were adjusted, and multi-interface coupled indium phosphide quantum dots of red, green, and blue light-emitting colors were synthesized, and electroluminescent LED devices of the three light-emitting colors were prepared, which met the needs of color modulation of electroluminescent LEDs.

[0049] Example 4

[0050] Indium chloride and oleylamine were mixed in a molar ratio of 1:15, placed in a container of a heating device, stirred, vacuumed, and heated to 120°C to obtain an indium precursor solution with a concentration of 0.12 moles; tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed in a molar ratio of 1:3 to obtain a phosphine precursor solution with a concentration of 3.6 moles; under inert gas protection, 10 milliliters of the indium precursor solution was heated to 200°C, 4.5 millimoles of the phosphine precursor solution was injected, and the temperature was maintained for 40 minutes. The temperature was increased to 350°C, 16 milliliters of zinc oleate with a concentration of 0.5 moles and 3 milliliters of tri-n-octylphosphine-selenium with a concentration of 2 moles were mixed and then injected into the reaction system, and the temperature was maintained for 80 minutes. Then, 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles was injected, and the temperature was maintained for 40 minutes. The temperature was increased to 360°C, 1.5 millimoles of a crosslinking agent and 5 milliliters of glycerol were injected, and the temperature was maintained for 30 minutes. The temperature was decreased to 260°C, 4 milliliters of zinc oleate with a concentration of 0.5 moles and 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles were injected, and the temperature was maintained for 30 minutes. The reaction solution was cooled to 30°C using a cold air gun, and the reaction was stopped. Ethanol was added, the reaction solution was centrifuged, and then repeated centrifugation was performed using n-hexane and ethanol for 5 times. Then, the solution was dissolved in n-octane to obtain a multi-interface coupled indium phosphide quantum dot solution with a concentration of 0.5 moles, which was used for subsequent preparation of light-emitting diodes.

[0051] A 0.5-molar-concentration poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) was printed on a transparent conductive substrate to form a 50-nanometer-thick hole injection layer, and then a 0.5-molar-concentration 1,2,4,5-tetra(trifluoromethyl)benzene was printed on the hole injection layer to form a 30-nanometer-thick hole transport layer, which was annealed at 100°C for 10 minutes. A 0.5-molar-concentration multi-interface coupled indium phosphide quantum dot solution was deposited on the hole transport layer and annealed at 30°C for 50 minutes to obtain a 20-nanometer-thick quantum dot light-emitting layer. A 0.5-molar-concentration magnesium-doped zinc oxide electron transport material was deposited on the multi-interface coupled indium phosphide quantum dot light-emitting layer and annealed at 40°C for 20 minutes to obtain a 30-nanometer-thick electron transport layer. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0052] Table 4 Influence of different crosslinking agents on the performance of electroluminescent LEDs

[0053]

[0054] Example 5

[0055] The indium chloride and oleylamine were mixed in a molar ratio of 1:15, placed in a container of a heating device, stirred, vacuumed, and heated to 120°C to obtain an indium precursor solution with a concentration of 0.12 moles; the tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed in a molar ratio of 1:3 to obtain a phosphine precursor solution with a concentration of 3.6 moles; under inert gas protection, 10 milliliters of the indium precursor solution was heated to 200°C, 4.5 millimoles of the phosphine precursor solution was injected, and the temperature was maintained for 40 minutes. The temperature was increased to 350°C, 16 milliliters of zinc oleate with a concentration of 0.5 moles and 3 milliliters of tri-n-octylphosphine-selenium with a concentration of 2 moles were mixed and then injected into the reaction system, and the temperature was maintained for 80 minutes. Then, 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles was injected, and the temperature was maintained for 40 minutes. The temperature was increased to 360°C, 1.5 millimoles of pentaerythritol tetra(3-mercaptopropionate) and 5 milliliters of a polar solvent were injected, and the temperature was maintained for 30 minutes. The temperature was decreased to 260°C, 4 milliliters of zinc oleate with a concentration of 0.5 moles and 1 milliliter of tri-n-octylphosphine-sulfur with a concentration of 2 moles were injected, and the temperature was maintained for 30 minutes. The reaction solution was cooled to 30°C using a cold air gun, and the reaction was stopped. Ethanol was added, the reaction solution was centrifuged, and then repeated centrifugation was performed using n-hexane and ethanol for 5 times. Then, the solution was dissolved in n-octane to obtain a multi-interface coupled indium phosphide quantum dot solution with a concentration of 0.5 moles, which was used for the preparation of a subsequent light-emitting diode.

[0056] A 50-nanometer-thick hole injection layer was printed on a transparent conductive substrate using a 0.5-molar-concentration poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), and then a 30-nanometer-thick hole transport layer was printed on the hole injection layer using a 0.5-molar-concentration 1,2,4,5-tetra(trifluoromethyl)benzene, and annealed at 100°C for 10 minutes. A 20-nanometer-thick quantum dot light-emitting layer was obtained by depositing a 0.5-molar-concentration multi-interface coupled indium phosphide quantum dot solution on the hole transport layer and annealing at 30°C for 50 minutes. A 30-nanometer-thick electron transport layer was obtained by depositing a 0.5-molar-concentration magnesium-doped zinc oxide electron transport material on the multi-interface coupled indium phosphide quantum dot light-emitting layer and annealing at 40°C for 20 minutes. A 70-nanometer-thick silver metal cathode was deposited on the electron transport layer by vacuum thermal evaporation.

[0057] Table 5 Influence of different polar solvents on the performance of the electroluminescent LED

[0058]

[0059] Example 6

[0060] Indium chloride and oleylamine were mixed at a molar ratio of 1:15 and placed in a container of a heating device. The mixture was stirred, evacuated, and heated to 120°C to obtain a 0.12 mol concentration indium precursor solution. Tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed at a molar ratio of 1:3 to obtain a 3.6 mol concentration phosphine precursor solution. Under inert gas protection, 10 mL of the indium precursor solution was heated to 200°C, and 4.5 mmol of the phosphine precursor solution was injected, maintaining this temperature for 40 minutes. The temperature was then raised to 350°C, and 16 mL of 0.5 mol zinc oleate and 3 mL of 2 mol tri-n-octylphosphine-selenium were mixed and injected into the reaction system. The mixture was maintained for 80 minutes, followed by the injection of 1 mL of 2 mol tri-n-octylphosphine-sulfur, maintaining this temperature for 40 minutes. The temperature was then raised to 360°C, and 1.5 mmol of pentaerythritol tetrakis(3-mercaptopropionic acid) and 5 mL of glycerol were injected, maintaining this temperature for 30 minutes. The temperature was lowered to 260°C, and 4 mL of 0.5 mol zinc oleate and 1 mL of 2 mol tri-n-octylphosphine-sulfur were injected. The mixture was kept at this temperature for 30 minutes, and then the reaction solution was cooled to 30°C using a cold air gun to stop the reaction. Ethanol was added, and the reaction solution was centrifuged. This centrifugation was repeated 5 times with hexane and ethanol, and then dissolved in n-octane to obtain a 0.5 mol multi-interface coupled indium phosphide quantum dot solution for subsequent light-emitting diode fabrication.

[0061] A 50 nm thick hole injection layer was formed by printing a 0.5 mol concentration of hole injection material onto a transparent conductive substrate. Subsequently, a 30 nm thick hole transport layer was formed by printing a 0.5 mol concentration of hole transport material onto the hole injection layer, and the layers were annealed at 100 °C for 10 minutes. A 0.5 mol concentration of multi-interface coupled indium phosphide quantum dot solution was deposited onto the hole transport layer and annealed at 30 °C for 50 minutes to obtain a 20 nm thick quantum dot emitting layer. A 0.5 mol concentration of magnesium-doped zinc oxide electron transport material was deposited onto the multi-interface coupled indium phosphide quantum dot emitting layer and annealed at 40 °C for 20 minutes to obtain a 30 nm thick electron transport layer. A 70 nm thick silver cathode was then deposited on the electron transport layer by vacuum thermal evaporation.

[0062] Table 6 Performance of electroluminescent LEDs with different hole injection / transport layers

[0063]

[0064] Summary: Example 6 adjusted the performance of the electroluminescent LED device by changing the hole injection layer and the hole transport layer. Electroluminescent LED devices with a single hole injection layer or hole transport layer have poor performance. A high-performance electroluminescent LED device was obtained by printing the hole injection layer first and then the hole transport layer.

[0065] Example 7

[0066] Indium chloride and oleylamine were mixed at a molar ratio of 1:15 and placed in a container of a heating device. The mixture was stirred, evacuated, and heated to 120°C to obtain a 0.12 mol concentration indium precursor solution. Tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed at a molar ratio of 1:3 to obtain a 3.6 mol concentration phosphine precursor solution. Under inert gas protection, 10 mL of the indium precursor solution was heated to 200°C, and 4.5 mmol of the phosphine precursor solution was injected, maintaining this temperature for 40 minutes. The temperature was then raised to 350°C, and 16 mL of 0.5 mol zinc oleate and 3 mL of 2 mol tri-n-octylphosphine-selenium were mixed and injected into the reaction system. The mixture was maintained for 80 minutes, followed by the injection of 1 mL of 2 mol tri-n-octylphosphine-sulfur, maintaining this temperature for 40 minutes. The temperature was then raised to 360°C, and 1.5 mmol of pentaerythritol tetrakis(3-mercaptopropionic acid) and 5 mL of glycerol were injected, maintaining this temperature for 30 minutes. The temperature was lowered to 260°C, and 4 mL of 0.5 mol zinc oleate and 1 mL of 2 mol tri-n-octylphosphine-sulfur were injected. The mixture was kept at this temperature for 30 minutes, and then the reaction solution was cooled to 30°C using a cold air gun to stop the reaction. Ethanol was added, and the reaction solution was centrifuged. This centrifugation was repeated 5 times with hexane and ethanol, and then dissolved in n-octane to obtain a 0.5 mol multi-interface coupled indium phosphide quantum dot solution for subsequent light-emitting diode fabrication.

[0067] A 50 nm thick hole injection layer was formed by printing 0.5 mol of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate. Subsequently, a 30 nm thick hole transport layer was formed by printing 0.5 mol of 1,2,4,5-tetrafluoromethylbenzene onto the hole injection layer, followed by annealing at 100 °C for 10 minutes. A 0.5 mol solution of multi-interface coupled indium phosphide quantum dot was deposited onto the hole transport layer and annealed at 30 °C for 50 minutes to obtain a 20 nm thick quantum dot emitting layer. A 0.5 mol solution of electron transport material was deposited onto the multi-interface coupled indium phosphide quantum dot emitting layer and annealed at 40 °C for 20 minutes to obtain a 30 nm thick electron transport layer. A 70 nm thick silver metal cathode was then deposited on the electron transport layer by vacuum thermal evaporation.

[0068] Table 7 Performance of electroluminescent LEDs with different electron transport layers

[0069]

[0070] Example 8

[0071] Indium chloride and oleylamine were mixed at a molar ratio of 1:15 and placed in a container of a heating device. The mixture was stirred, evacuated, and heated to 120°C to obtain a 0.12 mol concentration indium precursor solution. Tris(dimethylamino)phosphine and tri-n-octylphosphine were mixed at a molar ratio of 1:3 to obtain a 3.6 mol concentration phosphine precursor solution. Under inert gas protection, 10 mL of the indium precursor solution was heated to 200°C, and 4.5 mmol of the phosphine precursor solution was injected, maintaining this temperature for 40 minutes. The temperature was then raised to 350°C, and 16 mL of 0.5 mol zinc oleate and 3 mL of 2 mol tri-n-octylphosphine-selenium were mixed and injected into the reaction system. The mixture was maintained for 80 minutes, followed by the injection of 1 mL of 2 mol tri-n-octylphosphine-sulfur, maintaining this temperature for 40 minutes. The temperature was then raised to 360°C, and 1.5 mmol of pentaerythritol tetrakis(3-mercaptopropionic acid) and 5 mL of glycerol were injected, maintaining this temperature for 30 minutes. The temperature was lowered to 260°C, and 4 mL of 0.5 mol zinc oleate and 1 mL of 2 mol tri-n-octylphosphine-sulfur were injected. The mixture was kept at this temperature for 30 minutes, and then the reaction solution was cooled to 30°C using a cold air gun to stop the reaction. Ethanol was added, and the reaction solution was centrifuged. This centrifugation was repeated 5 times with hexane and ethanol, and then dissolved in n-octane to obtain a 0.5 mol multi-interface coupled indium phosphide quantum dot solution for subsequent light-emitting diode fabrication.

[0072] A 50 nm thick hole injection layer was formed by printing 0.5 mol of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid) onto a transparent conductive substrate. Subsequently, a 30 nm thick hole transport layer was formed by printing 0.5 mol of 1,2,4,5-tetrafluoromethylbenzene onto the hole injection layer, followed by annealing at 100 °C for 10 minutes. A 0.5 mol solution of multi-interface coupled indium phosphide quantum dot was deposited onto the hole transport layer and annealed at 30 °C for 50 minutes to obtain a 20 nm thick quantum dot emitting layer. A 0.5 mol solution of magnesium-doped zinc oxide electron transport material was deposited onto the multi-interface coupled indium phosphide quantum dot emitting layer and annealed at 40 °C for 20 minutes to obtain a 30 nm thick electron transport layer. A 70 nm thick metal cathode was then deposited on the electron transport layer by vacuum thermal evaporation.

[0073] Table 8 Performance of Electroluminescent LEDs with Different Metal Cathodes

[0074]

[0075] Comparative Example

[0076] To compare the superiority of the multi-interface coupled indium phosphide quantum dots of this invention, Example 8 uses uncoupled quantum dots to fabricate a light-emitting diode (LED), which is then compared with an LED fabricated using multi-interface coupled indium phosphide quantum dots (taking Example 1 as an example). The fabrication process of the uncoupled quantum dot LED is the same as in Example 1, except that the steps of injecting crosslinking agent and polar solvent and holding at a temperature are omitted. The results show that compared with the LED fabricated using uncoupled indium phosphide quantum dots, the LED fabricated using multi-interface coupled indium phosphide quantum dots of this invention has a higher external quantum efficiency. This is because the unique coupling structure significantly reduces surface defects and achieves a higher fluorescence quantum yield.

[0077] Table 9 Performance of Quantum Dots and Their Electroluminescent LEDs

[0078]

[0079] While several embodiments of the present invention have been provided herein, those skilled in the art should understand that modifications can be made to these embodiments without departing from the spirit of the invention. The above embodiments are merely exemplary and should not be construed as limiting the scope of the invention.

Claims

1. A method for preparing multi-interface coupled indium phosphide quantum dots, characterized in that: The one-step continuous synthesis of the multi-interface coupled core-shell structure InP / ZnSe / ZnS quantum dots comprises the following steps: (1) Put halogenated indium and oleylamine in a flask, heat, stir and vacuumize to obtain an indium source solution with a concentration of 0.07-0.12 mol, and then heat to 160-200℃, quickly inject tri(dimethylamino) phosphine solution, and keep the molar ratio of phosphorus to indium at 3:1-5:1 for 20-40 minutes; (2) Heat to 300-350℃, inject 0.3-0.5 mol zinc oleate and 1-2 mol tri-n-octylphosphine-selenium mixture into the reaction system, keep for 40-80 minutes, then inject 1-2 mol tri-n-octylphosphine-sulfur, and keep for 20-40 minutes; (3) Heat to 340-360℃, inject 0.5-1.5 mol polar solvent and 3-5 ml crosslinking agent, and keep for 15-30 minutes; (4) Reduce the temperature to 220-260℃, inject 1-2 mol zinc oleate and tri-n-octylphosphine-sulfur, and keep for 15-30 minutes to stop the reaction; (5) Add ethanol or acetone, centrifuge the reaction solution, repeat the centrifugation with n-hexane and ethanol, and then dissolve in an organic solvent to obtain a multi-interface coupled InP quantum dot solution. The polar solvent is glycerol and / or ethylene glycol, and the crosslinking agent is tetra(3-mercaptopropionic acid) pentaerythritol ester and / or tetra(2-mercaptoacetic acid) pentaerythritol ester. 2.The method of claim 1, wherein the method further comprises: adding a first surfactant to the solution of the first precursor and the second precursor to form a first mixture; and adding a second surfactant to the first mixture to form a second mixture. The halogenated indium is indium chloride, indium bromide or indium iodide. 3.The method of claim 1, wherein the method further comprises: adding a surfactant to the solution of the indium phosphide quantum dots to form a surfactant-modified indium phosphide quantum dot solution. The organic solvent is n-octane, toluene or dichloromethane.

4. A multi-interface coupled indium phosphide quantum dot electroluminescent diode, characterized in that: The multi-interface coupled InP quantum dot solution prepared by the preparation method of any one of claims 1-3 is used to prepare a light-emitting layer in a diode.

5. The method for fabricating a multi-interface coupled indium phosphide quantum dot electroluminescent diode according to claim 4, characterized in that, The preparation steps are as follows: (1) Print a hole injection material on a transparent conductive substrate to form a 50-70 nm thick hole injection layer, then print a hole transport material on the hole injection layer to form a 30-50 nm thick hole transport layer, and anneal at 100-150℃ for 10-30 minutes; (2) Deposit the multi-interface coupled InP quantum dot solution on the hole transport layer to form a 20-50 nm thick multi-interface coupled InP quantum dot light-emitting layer, and anneal at 50-80℃ for 20-40 minutes; (3) Print a 0.5-1.5 mol zinc oxide or magnesium-doped zinc oxide ethanol solution on the quantum dot layer to form a 30-50 nm thick electron transport layer, and anneal at 40-80℃ for 20-40 minutes; (4) Deposit a metal cathode material on the electron transport layer by vacuum evaporation to form a 70-100 nm thick electrode, and obtain an electroluminescent diode.

6. The method of claim 5, wherein the method further comprises: The hole injection material is poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonic acid), and the hole transport layer material is one of 1,2,4,5-tetrakis(trifluoromethyl)benzene, poly(9-vinylcarbazole) and poly[bis(4-phenyl)(4-butylphenyl)amine].

7. The method for fabricating a multi-interface coupled indium phosphide quantum dot electroluminescent diode according to claim 6, characterized in that: The transparent conductive substrate is one of indium-doped tin oxide and silver nanowires, and the metal cathode material is one of aluminum, silver and gold.

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