CN112349870B - Quantum dot light-emitting diode and preparation method thereof - Google Patents

Quantum dot light-emitting diode and preparation method thereof Download PDF

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CN112349870B
CN112349870B CN201910730700.9A CN201910730700A CN112349870B CN 112349870 B CN112349870 B CN 112349870B CN 201910730700 A CN201910730700 A CN 201910730700A CN 112349870 B CN112349870 B CN 112349870B
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quantum dot
dot light
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CN112349870A (en
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何斯纳
吴龙佳
吴劲衡
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TCL Technology Group Co Ltd
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    • H10K50/14—Carrier transporting layers
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    • H10K50/11—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers
    • H10K50/115—OLEDs or polymer light-emitting diodes [PLED] characterised by the electroluminescent [EL] layers comprising active inorganic nanostructures, e.g. luminescent quantum dots
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Abstract

The invention belongs to the technical field of display, and particularly relates to a quantum dot light-emitting diode and a preparation method thereof. The quantum dot light-emitting diode comprises an anode, a cathode and a quantum dot light-emitting layer, wherein the quantum dot light-emitting layer is positioned between the anode and the cathode, an electron transmission layer is arranged between the cathode and the quantum dot light-emitting layer, and an ethylene diamine tetraacetic acid disodium material is arranged on at least part of the surface, close to the quantum dot light-emitting layer, of the electron transmission layer. The device well utilizes the high electron mobility of the electron transport material and the energy level potential barrier between the quantum dot light emitting layer and the electrode can be reduced by the EDTA-2Na, so that ohmic contact is formed to effectively transport charges, good contact can be generated between the EDTA-2Na and the electron transport material, a proper electron transport channel is provided, good electron transport and electron injection are achieved, holes are effectively blocked, exciton recombination is reduced, and finally the light emitting efficiency and the performance of the device are improved.

Description

Quantum dot light-emitting diode and preparation method thereof
Technical Field
The invention belongs to the technical field of display, and particularly relates to a quantum dot light-emitting diode and a preparation method thereof.
Background
The Quantum Dots (QDs) of the semiconductor have Quantum size effect, people can realize the required luminescence with specific wavelength by regulating and controlling the size of the QDs, and the tuning range of the luminescence wavelength of the CdSe QDs can be from blue light to red light. In the conventional inorganic electroluminescent device, electrons and holes are injected from a cathode and an anode, respectively, and then recombined in a light emitting layer to form excitons for light emission. Conduction band electrons in wide bandgap semiconductors can be accelerated under high electric fields to obtain high enough energy to strike QDs to cause it to emit light.
In recent years, inorganic semiconductors have been studied as an electron transport layer in a relatively hot manner. Nanometer ZnO and ZnS are wide bandgap semiconductor materials, and attract the attention of a plurality of researchers due to the advantages of quantum confinement effect, size effect, excellent fluorescence characteristic and the like. Therefore, in the last ten years, znO and ZnS nanomaterials have shown great potential for development in the fields of photocatalysis, sensors, transparent electrodes, fluorescent probes, diodes, solar cells, and lasers. ZnO is an n-type semiconductor material with a direct band gap, has a wide forbidden band of 3.37eV and a low work function of 3.7eV, and the structural characteristics of the energy band determine that ZnO can become a proper electron transport layer material. Meanwhile, znS is a II-VI semiconductor material, has two different structures of sphalerite and wurtzite, and has the characteristics of stable chemical property of forbidden bandwidth (3.62 eV), abundant resources, low price and the like.
The interface chemical modification can change the intrinsic physical properties of the superconducting, metallic, semi-metallic and semiconducting electronic structures by changing the electronic structures, thereby inducing electron transfer or lattice change. Therefore, the method becomes an effective method for regulating and controlling the intrinsic physical properties of the inorganic nano material. However, the interface modification effect of inorganic semiconductors as electron transport layers in devices is not yet ideal.
Therefore, the prior art is still to be improved.
Disclosure of Invention
The invention aims to provide a quantum dot light-emitting diode and a preparation method thereof, and aims to solve the technical problem that the luminous efficiency of a device is influenced due to the fact that the electron transmission effect of the conventional quantum dot light-emitting diode is not ideal.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a quantum dot light-emitting diode, which comprises an anode, a cathode and a quantum dot light-emitting layer positioned between the anode and the cathode, wherein an electron transmission layer is arranged between the cathode and the quantum dot light-emitting layer, and an ethylene diamine tetraacetic acid disodium material is arranged on the surface, close to the quantum dot light-emitting layer, of the electron transmission layer.
In the quantum dot light-emitting diode provided by the invention, the electron transmission layer and the ethylene diamine tetraacetic acid disodium material are arranged between the cathode and the quantum dot light-emitting layer, the ethylene diamine tetraacetic acid disodium material is arranged on at least part of the surface of the electron transmission layer close to the quantum dot light-emitting layer, and the ethylene diamine tetraacetic acid disodium material can reduce the work function of the electron transmission material, so that the injection barrier is reduced, the contact resistance is reduced, and the electron transmission is promoted; meanwhile, the disodium ethylene diamine tetraacetate material is arranged on at least part of the surface of the electron transmission layer close to the quantum dot light emitting layer, so that the disodium ethylene diamine tetraacetate material has the characteristic of high electron mobility of the electron transmission material, and can reduce the energy level potential barrier between the quantum dot light emitting layer and an electrode, thereby forming ohmic contact to effectively transmit charges, and the disodium ethylene diamine tetraacetate and the electron transmission material can generate good contact, so that a proper electron transmission channel can be provided, good electron transmission and electron injection can be achieved, holes can be effectively blocked, exciton recombination can be reduced, and the light emitting efficiency and the service performance of a device can be finally improved.
The invention provides a preparation method of a quantum dot light-emitting diode, which comprises the following steps:
providing an anode substrate;
preparing a quantum dot light emitting layer on the anode substrate;
preparing an ethylene diamine tetraacetic acid disodium material on at least part of the surface of the quantum dot light-emitting layer;
preparing an electron transport layer on the surface of the ethylene diamine tetraacetic acid material;
preparing a cathode on the electron transport layer.
And, a method for preparing quantum dot light emitting diode, comprising the steps of:
providing a cathode substrate;
preparing an electron transport layer on the cathode substrate;
preparing an ethylene diamine tetraacetic acid disodium material on at least part of the surface of the electron transport layer;
preparing a quantum dot light-emitting layer on the surface of the ethylene diamine tetraacetic acid material;
and preparing an anode on the quantum dot light-emitting layer.
The invention provides a preparation method of an upright quantum dot light-emitting diode and an inverted quantum dot light-emitting diode respectively, the preparation method is simple and easy to implement and is suitable for large-area and large-scale preparation, and in a finally obtained device, an ethylene diamine tetraacetic acid disodium material is prepared on the contact surface of an electron transmission layer and a quantum dot light-emitting layer, and can reduce the work function of the electron transmission material, so that the injection barrier is reduced, and the contact resistance is reduced.
Drawings
Fig. 1 is a schematic structural diagram of a quantum dot light-emitting diode provided by the present invention;
FIG. 2 is a schematic flow chart of a method for manufacturing an upright quantum dot light-emitting diode according to the present invention;
fig. 3 is a schematic flow chart of a method for manufacturing an inversion-type quantum dot light-emitting diode according to the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
On one hand, the embodiment of the invention provides a quantum dot light-emitting diode, which comprises an anode, a cathode and a quantum dot light-emitting layer positioned between the anode and the cathode, wherein an electron transmission layer is arranged between the cathode and the quantum dot light-emitting layer, and an ethylene diamine tetraacetic acid disodium material is arranged on at least part of the surface, close to the quantum dot light-emitting layer, of the electron transmission layer.
In the quantum dot light-emitting diode provided by the embodiment of the invention, the electron transmission layer and the ethylene diamine tetraacetic acid disodium material are stacked between the cathode and the quantum dot light-emitting layer, the ethylene diamine tetraacetic acid disodium material is arranged on at least part of the surface of the electron transmission layer close to the quantum dot light-emitting layer, and the ethylene diamine tetraacetic acid disodium material can reduce the work function of the electron transmission material, so that the injection barrier is reduced, the contact resistance is reduced, and the electron transmission is promoted; meanwhile, the disodium ethylene diamine tetraacetate material is arranged on at least part of the surface of the electron transmission layer close to the quantum dot light emitting layer, so that the characteristic of high electron mobility of the electron transmission material is achieved, the characteristic that the energy level potential barrier between the quantum dot light emitting layer and an electrode can be reduced by the disodium ethylene diamine tetraacetate material, ohmic contact is formed to effectively transmit charges, good contact can be generated between the disodium ethylene diamine tetraacetate and the electron transmission material, a proper electron transmission channel can be provided, good electron transmission and electron injection are achieved, holes are effectively blocked, exciton recombination is reduced, and the light emitting efficiency and the use performance of the device are finally improved.
In one embodiment, the ethylene diamine tetraacetic acid disodium material is arranged on a part of the surface of the electron transport layer close to the quantum dot light emitting layer, and at this time, the ethylene diamine tetraacetic acid disodium material is not arranged on the other part of the surface of the electron transport layer close to the quantum dot light emitting layer, or other materials are arranged according to the specific needs of the device. When the ethylene diamine tetraacetic acid material is arranged on the part of the surface of the electron transmission layer close to the quantum dot light-emitting layer, the work function of the electron transmission material can be reduced due to the ethylene diamine tetraacetic acid material, so that the electron injection potential barrier on the surface provided with the ethylene diamine tetraacetic acid material can be reduced, the contact resistance is reduced, and the electron transmission is promoted. Meanwhile, the ethylene diamine tetraacetic acid disodium material is arranged on part of the surface, a proper electron transmission channel can be provided between the ethylene diamine tetraacetic acid disodium material and the electron transmission material, so that good electron transmission and electron injection are achieved, holes are effectively blocked, exciton recombination is reduced, and the luminous efficiency and the service performance of the device are finally improved.
In a preferred embodiment, the ethylene diamine tetraacetic acid material on the surface of the electron transport layer close to the quantum dot light-emitting layer forms an ethylene diamine tetraacetic acid disodium material layer, namely, the electron transport layer is close to the whole surface of the quantum dot light-emitting layerAnd forming the ethylene diamine tetraacetic acid disodium material layer. Disodium ethylene diamine tetraacetate, EDTA-2Na for short, is a non-conjugated micromolecular electrolyte, has carboxyl (-COOH) on the structure, can be dissolved in some organic solvents (such as methanol, isopropanol and the like), and also has certain conductivity. Because EDTA-2Na contains more carboxyl groups, the molecules or intermolecular are gathered together due to the action of hydrogen bonds, and Na is treated by an external voltage + The activity of the compound is increased, so that the acting force between carboxyl groups is weakened, and the compound is more fully contacted with an electron transmission material, so that the interface modification performance of the compound is improved, namely EDTA-2Na can play a good role in interface modification between an electron transmission layer and a quantum dot light-emitting layer; because the electron transport material has higher electron mobility, but has the defects of more surface defects and uneven spatial distribution, when EDTA-2Na forms an EDTA-2Na layer between the electron transport layer and the quantum dot light-emitting layer, namely an interface dipole layer is formed, the electron transport is further promoted, and the electron transport layer and the EDTA-2Na layer which are laminated can better utilize the high electron mobility of the electron transport material, and the EDTA-2Na layer can reduce the energy level barrier between the light-emitting layer and an electrode, so that better ohmic contact is formed to effectively transport charges.
In one embodiment, the thickness of the ethylene diamine tetraacetic acid material layer in the quantum dot light-emitting diode is 20-60nm; the EDTA-2Na layer is too thin to well cover the EDTA-2Na layer of the adjacent layer and is too thick, the electron mobility of the EDTA-2Na is poor, and the performance of the device is influenced, so that the comprehensive effect within the range of 20-60nm is optimal. Further, the thickness of the electron transport layer is 20-60nm.
In one embodiment, the material of the electron transport layer in the quantum dot light emitting diode is selected from ZnO, znS and TiO 2 、SnO 2 、Ta 2 O 3 And ZrO 2 Preferably ZnO nanoparticles or ZnS nanoparticles.
In one embodiment, an electron injection layer is arranged between the electron transport layer and the cathode in the quantum dot light emitting diode; in another embodiment, a hole function layer, such as a hole transport layer, or a stacked hole injection layer and hole transport layer (where the hole injection layer is adjacent to the anode) is disposed between the quantum dot light emitting layer and the anode.
In a specific embodiment, the structure of the positive quantum dot light emitting diode is shown in fig. 1, and the device sequentially comprises a substrate 1, an anode 2, a hole transport layer 3, a quantum dot light emitting layer 4, an EDTA-2Na layer 5, an electron transport layer 6 and a cathode 7 which are stacked from bottom to top.
On the other hand, the embodiment of the present invention further provides a method for manufacturing a quantum dot light emitting diode, where the quantum dot light emitting diode is an orthotype device, as shown in fig. 2, and the method includes the following steps:
s01: providing an anode substrate;
s02: preparing a quantum dot light emitting layer on the anode substrate;
s03: preparing an ethylene diamine tetraacetic acid disodium material on at least part of the surface of the quantum dot light-emitting layer;
s04: preparing an electron transport layer on the surface of the ethylene diamine tetraacetic acid material;
s05: preparing a cathode on the electron transport layer.
And, a method for preparing a quantum dot light emitting diode, which is an inversion type device, as shown in fig. 3, comprising the steps of:
e01: providing a cathode substrate;
e02: preparing an electron transport layer on the cathode substrate;
e03: preparing an ethylene diamine tetraacetic acid disodium material on at least part of the surface of the electron transport layer;
e04: preparing a quantum dot light-emitting layer on the surface of the ethylene diamine tetraacetic acid material;
e05: and preparing an anode on the quantum dot light-emitting layer.
The embodiment of the invention provides a preparation method of an upright quantum dot light-emitting diode and an inverted quantum dot light-emitting diode respectively, the preparation method is simple and easy to implement and is suitable for large-area and large-scale preparation, in a finally obtained device, an ethylene diamine tetraacetic acid material is prepared on at least part of the contact surface of an electron transmission layer and a quantum dot light-emitting layer, and the ethylene diamine tetraacetic acid material can reduce the work function of the electron transmission material, so that an injection barrier is reduced, and the contact resistance is reduced.
For the preparation method of the positive quantum dot light-emitting diode, in step S03: the step of preparing the ethylene diamine tetraacetic acid disodium material on at least part of the surface of the quantum dot light-emitting layer comprises the following steps: and preparing a disodium ethylene diamine tetraacetate solution, depositing the disodium ethylene diamine tetraacetate solution on at least part of the surface of the quantum dot light-emitting layer, and then carrying out annealing treatment.
Further, the ethylene diamine tetraacetic acid disodium solution is deposited on the surface of the quantum dot light-emitting layer, and then an ethylene diamine tetraacetic acid disodium layer is formed after annealing treatment so as to cover the surface of the quantum dot light-emitting layer. After the electron transport layer is subsequently prepared, the laminated electron transport layer and the EDTA-2Na layer are formed, so that the high electron mobility of the electron transport material can be better utilized, and the energy level barrier between the light emitting layer and the electrode can be reduced by the EDTA-2Na, so that better ohmic contact can be formed to effectively transport charges.
Wherein, the solvent in the ethylene diamine tetraacetic acid disodium solution is at least one selected from methanol, ethanol, isopropanol and dimethyl sulfoxide, and dimethyl sulfoxide (DMSO) is preferred; the concentration of the ethylene diamine tetraacetic acid disodium in the ethylene diamine tetraacetic acid disodium solution is 10-20mg/ml; if the concentration is too low, the prepared EDTA-2Na layer is too thin and cannot well cover the quantum dot light emitting layer, and if the concentration is too high, the prepared EDTA-2Na layer is too thick and influences the performance of the device. Further, the temperature of the annealing treatment is 100-150 ℃; the time of the annealing treatment is 10-20min. In one embodiment, the step of preparing the disodium edetate solution comprises: dissolving EDTA-2Na in DMSO to form EDTA-2Na solution; the concentration of EDTA-2Na solution is: 10-20mg/ml.
In the step S04: the step of preparing the electron transport layer on the surface of the ethylene diamine tetraacetic acid disodium material comprises the following steps: preparing precursor solution of electron transport material (including dissolving metal salt such as zinc salt in organic solvent, stirring at constant temperature for dissolving, adding alkali solution (sulfur source), stirring at constant temperature, cooling, precipitating with precipitant, washing, and drying); and then dripping the precursor solution on the surface of the EDTA-2Na layer, and carrying out spin coating and annealing to form a film so as to form a laminated structure of the EDTA-2Na layer and the electron transport layer.
The metal salt is zinc salt, titanium salt, tin salt, zirconium salt and the like which can be used as corresponding metal salts of the electron transport material. Wherein the zinc salt is soluble inorganic zinc salt or organic zinc salt, such as zinc acetate, zinc nitrate, zinc chloride, zinc sulfate, zinc acetate dihydrate, etc., but not limited thereto. The organic solvent is not limited thereto, but isopropyl alcohol, ethanol, propanol, butanol, methanol, etc. The alkali solution is ammonia, potassium hydroxide, sodium hydroxide, lithium hydroxide, ethanolamine, ethylene glycol, diethanolamine, triethanolamine, ethylenediamine, etc., but is not limited thereto. The sulfur source is not limited to sodium sulfide, potassium sulfide, thiourea, amine sulfide, etc. The precipitant is a weakly polar and non-polar solvent such as ethyl acetate, heptane, octane, etc., but not limited thereto. The total concentration of the metal salt solution is 0.2M-1M; molar ratio, base: m 2+ = (1.8 to 2.5): 1,pH =12 to 13; molar ratio, S 2- ：Zn 2+ In a molar ratio of (1-1.5): 1; . The temperature is 60-80 ℃; the reaction time is 2-4 h.
The electron transport material layer is exemplified by a ZnO layer and a ZnS layer:
the zinc hydroxide (Zn (OH) is generated by the reaction of zinc salt and alkali liquor in the embodiment of the invention 2 )，Zn(OH) 2 Polycondensation reaction is carried out, and ZnO nuclear crystal particles are generated after dehydration. In the zinc oxide crystal solution, the organic base and/or inorganic baseMolar amount of base the ratio of base to zinc ion is (1.8-2.5): 1, when the ratio of the sum of the molar amounts of base and zinc ions is less than 1.8:1, excessive zinc salt and less alkali liquor can not generate enough zinc hydroxide; greater than 2.5:1, too high a pH results in a slower polycondensation rate in the system. Optimally, the ratio of base to zinc ions is maintained at (1.8-2.5): when the pH value is 1, the pH value is = 12-13, and ZnO nano-particles with uniform particles can be obtained subsequently.
In the embodiment of the invention, znS is generated by reacting zinc salt with a sulfur source. Wherein the ratio of the molar amount of sulfur in the sulfur source to the molar amount of zinc ions in the zinc salt is (1-1.5): 1, when the molar ratio of sulfur to indium ions is less than 1:1, excessive zinc salt and less sulfur are generated, so that the generated zinc sulfide is insufficient; greater than 1.5: in case 1, the sulfur salt is excessive, and thus, an impurity compound is easily formed and is not easily removed. Optimally, the ratio of the molar amount of sulfur to the molar amount of zinc ions is (1-1.5): 1, a compact and dense film can be obtained subsequently, and the particles on the surface of the film are uniformly distributed.
The annealing temperature of the EDTA-Na layer is selected to be 100 to 150 ℃ in order to remove the solvent. The annealing temperature of the electron transporting material layer is selected to be 250 to 300 ℃ in order to remove the solvent and to make the electron transporting material more crystalline.
For the preparation method of the inverted quantum dot light-emitting diode, in the step E03: the step of preparing the ethylene diamine tetraacetic acid disodium material on at least part of the surface of the electron transport layer comprises the following steps: preparing a disodium ethylene diamine tetraacetate solution, depositing the disodium ethylene diamine tetraacetate solution on at least part of the surface of the electron transport layer, and then carrying out annealing treatment.
Further, the ethylene diamine tetraacetic acid disodium solution is deposited on the surface of the electron transport layer, and then annealing treatment is carried out to form an ethylene diamine tetraacetic acid disodium layer to cover the surface of the electron transport layer. This makes it possible to form a stacked electron transport layer and an EDTA-2Na layer to make good use of the high electron mobility of the electron transport material and the EDTA-2Na can reduce the energy level barrier between the light emitting layer and the electrode, thereby forming a better ohmic contact to efficiently transport charges.
The solvent selection, the concentration selection, the annealing temperature and the annealing time of the disodium ethylene diamine tetraacetate solution and the like can be the same as the preparation method of the positive quantum dot light-emitting diode. Namely, the solvent in the ethylene diamine tetraacetic acid disodium solution is at least one selected from methanol, ethanol, isopropanol and dimethyl sulfoxide, and dimethyl sulfoxide (DMSO) is preferred; the concentration of the ethylene diamine tetraacetic acid in the ethylene diamine tetraacetic acid disodium solution is 10-20mg/ml; if the concentration is too low, the prepared EDTA-2Na layer is too thin to cover the electron transport layer well, and if the concentration is too high, the prepared EDTA-2Na layer is too thick, which affects the performance of the device. Further, the temperature of the annealing treatment is 100-150 ℃; the time of the annealing treatment is 10-20min.
In one embodiment, the method for preparing the positive type QLED device with the laminated structure of the EDTA-2Na layer and the electron transmission layer comprises the following steps:
a: firstly, growing a hole transport layer on a substrate;
b: then depositing a quantum dot light-emitting layer on the hole transport layer;
c: and finally, sequentially depositing EDTA-2Na and an electron transmission material on the quantum dot light-emitting layer, and evaporating a cathode on the electron transmission layer to obtain the quantum dot light-emitting diode.
In order to obtain a high-quality stacked structure of EDTA-2Na and an electron transport material, the ITO substrate needs to be subjected to a pretreatment process. The method comprises the following steps: cleaning the whole piece of ITO conductive glass with a cleaning agent, preliminarily removing stains on the surface, then sequentially carrying out ultrasonic cleaning in deionized water, acetone, absolute ethyl alcohol and deionized water for 20min respectively to remove impurities on the surface, and finally blowing dry with high-purity nitrogen to obtain the ITO positive electrode substrate.
The hole transport layer may be made of a hole transport material conventional in the art, including but not limited to TFB, PVK, poly-TPD, TCTA, PEDOT: PSS, CBP, etc., or any combination thereof, as well as other high performance hole transport materials. The preparation of the hole transport layer comprises: placing the ITO substrate on a spin coater, and spin-coating a prepared solution of a hole transport material to form a film; the film thickness is controlled by adjusting the concentration of the solution, the spin-coating speed and the spin-coating time, and then a thermal annealing process is performed at an appropriate temperature.
The light-emitting quantum dots in the quantum dot light-emitting layer are oil-soluble quantum dots and comprise binary phase, ternary phase and quaternary phase quantum dots; wherein the binary phase quantum dots include CdS, cdSe, cdTe, inP, agS, pbS, pbSe, hgS, etc., but are not limited thereto, and the ternary phase quantum dots include Zn X Cd 1-X S、Cu X In 1-X S、Zn X Cd 1-X Se、Zn X Se 1-X S、Zn X Cd 1-X Te、PbSe X S 1-X Etc. are not limited thereto, and the quaternary phase quantum dots include, zn X Cd 1-X S/ZnSe、Cu X In 1-X S/ZnS、Zn X Cd 1-X Se/ZnS、CuInSeS、Zn X Cd 1-X Te/ZnS、PbSe X S 1-X the/ZnS and the like are not limited thereto. The quantum dots can be any one of the common red, green and blue quantum dots or other yellow light, and the quantum dots can contain cadmium or do not contain cadmium. The quantum dot light-emitting layer of the quantum dot material has the characteristics of wide excitation spectrum, continuous distribution, high stability of emission spectrum and the like. The preparation of the quantum dot light-emitting layer comprises the following steps: spin-coating the prepared luminescent material solution with a certain concentration on a spin coater of a substrate with a spin-coated hole transport layer to form a film, controlling the thickness of the luminescent layer to be about 20-60nm by adjusting the concentration of the solution, the spin-coating speed and the spin-coating time, and drying at a proper temperature.
The preparation method of the EDTA-2Na layer and the electron transport layer of the stacked structure is a spin coating process, and includes, but is not limited to, drop coating, spin coating, dipping, coating, printing, evaporation, and the like. The method specifically comprises the following steps: the substrate which is coated with the quantum dot luminescent layer by spin coating is placed on a spin coater, EDTA-2Na solution and electron transmission material solution which are prepared with certain concentration are respectively coated by spin coating and annealed to form a film in sequence, and the thicknesses of the EDTA-2Na layer and the electron transmission layer are controlled by adjusting the concentration of the solution, the spin coating speed (preferably, the rotating speed is between 2000 and 6000 rpm) and the spin coating time, wherein the thicknesses are respectively about 20 to 60nm. The step can be performed in air annealing or in nitrogen atmosphere, and the annealing atmosphere is selected according to actual requirements.
And then, the substrate deposited with the functional layers is placed in an evaporation bin, and a layer of 15-30nm metal silver or aluminum is thermally evaporated through a mask plate to serve as a cathode, or a nano Ag wire or a Cu wire is used, so that a carrier can be smoothly injected due to the small resistance.
Further, the obtained QLED is subjected to a packaging process, which may be performed by a conventional machine or by a manual method. Preferably, the oxygen content and the water content in the packaging treatment environment are both lower than 0.1ppm so as to ensure the stability of the device.
The invention is described in further detail with reference to a part of the test results, which are described in detail below with reference to specific examples.
Example 1
The preparation of the laminated structure of the EDTA-2Na layer and the ZnO electron transport layer will be described in detail by taking zinc acetate, ethanol, potassium hydroxide, EDTA-2Na, and DMSO as examples.
1) An appropriate amount of zinc acetate was first added to 50ml of ethanol to form a solution having a total concentration of 0.5M. Then dissolved by stirring at 70 ℃, and added with alkali solution (molar ratio, OH) of potassium hydroxide dissolved in 10ml of ethanol - ：Zn 2+ =2:1,ph = 12). Stirring was continued at 70 ℃ for 4h to give a homogeneous, clear solution. And then, after the solution is cooled, ethyl acetate is used for precipitation, after centrifugation, a small amount of ethanol is used for dissolution (repeated operation and 3 times of washing), drying is carried out, znO nanoparticles are prepared, and the ZnO solution is obtained by re-dissolving the nanoparticles.
2) Subsequently, an appropriate amount of EDTA-2Na was dissolved in DMSO to form a 10mg/ml EDTA-2Na solution.
3) Finally, on the processed substrate, performing spin coating on the EDTA-2Na solution by using a spin coater and annealing at 150 ℃; and dripping the ZnO solution on a substrate, spin-coating at 300 ℃, and annealing to form a film to form an EDTA-2Na layer/ZnO electron transport layer laminated structure.
Example 2
The preparation of the laminated structure of the EDTA-2Na layer and the ZnO electron transport layer will be described in detail by taking zinc nitrate, methanol, ethanolamine, EDTA-2Na, DMSO as examples.
1) An appropriate amount of zinc nitrate was first added to 50ml of methanol to form a solution having a total concentration of 0.5M. Then stirring at 60 deg.C to dissolve, adding alkaline solution (molar ratio, ethanolamine: zn) of ethanolamine dissolved in 10ml methanol 2+ =2.5:1,ph = 13). Stirring was continued at 60 ℃ for 4h to give a homogeneous, clear solution. And then, after the solution is cooled, the solution is separated out by using heptane, after centrifugation, the solution is dissolved by using a small amount of methanol (repeated operation and washing for 3 times), and the solution is dried to prepare ZnO nanoparticles, and the ZnO solution is obtained by re-dissolving the nanoparticles.
2) Subsequently, an appropriate amount of EDTA-2Na was dissolved in DMSO to form a 10mg/ml EDTA-2Na solution.
3) Finally, on the processed substrate, performing spin coating on the EDTA-2Na solution by using a spin coater and annealing at 150 ℃; and dripping the ZnO solution on a substrate, spin-coating at 300 ℃, and annealing to form a film, thereby forming an EDTA-2Na layer/ZnO electron transport layer laminated structure.
Example 3
The preparation of the stacked structure of the EDTA-2Na layer and the ZnS electron transport layer will be described in detail by taking zinc chloride, propanol, sodium sulfide, EDTA-2Na, DMSO as examples.
1) An appropriate amount of zinc chloride was added to 50ml of propanol to form a solution having a total concentration of 0.5M, and dissolved with stirring at 80 ℃. A solution of sodium sulfide dissolved in 10ml of ethanol (molar ratio, S) was added 2- ：Zn 2+ ＝1.2：
1). Stirring was continued at 80 ℃ for 4h to give a homogeneous solution. And then, after the solution is cooled, precipitating by using ethyl acetate, centrifuging, dissolving by using a small amount of ethanol (repeating the operation, washing for 3 times), drying to obtain ZnS nanoparticles, and re-dissolving the nanoparticles to obtain the ZnS solution.
2) Subsequently, an appropriate amount of EDTA-2Na was dissolved in DMSO to form a 10mg/ml EDTA-2Na solution.
3) Finally, on the processed substrate, performing spin coating on EDTA-2Na by a spin coater and annealing at 150 ℃; and dripping the ZnS solution on a substrate, spin-coating at 300 ℃, and annealing to form a film, thereby forming an EDTA-2Na layer/ZnS electron transport layer laminated structure.
Example 4
A method for preparing a QLED device, the structure of which is shown in figure 1, comprises the following steps:
a: firstly, growing a hole transport layer on an anode substrate;
b: then depositing a quantum dot light-emitting layer on the hole transport layer;
c: finally, an EDTA-2Na layer and an electron transport layer are sequentially deposited on the quantum dot light-emitting layer, and the EDTA-2Na layer and the electron transport layer are laminated and prepared according to the method in the embodiment 1;
d: and evaporating a cathode on the electron transmission layer to obtain the quantum dot light-emitting diode.
The QLED device of the present embodiment is of an upright configuration, and as shown in fig. 1, the QLED device includes, in order from bottom to top, a substrate 1, an anode 2, a hole transport layer 3, a quantum dot light emitting layer 4, an EDTA-2Na layer 5, an electron transport layer 6, and a cathode 7. The substrate 1 is made of a glass sheet, the anode 2 is made of an ITO substrate, the hole transport layer 3 is made of TFB, the quantum dot light emitting layer 4 is made of quantum dots, the EDTA-2Na layer 5 is made of EDTA-2Na, the electron transport layer 5 is made of ZnO nanoparticles, and the cathode 6 is made of Al.
Example 5
A method for preparing a QLED device, the structure of which is shown in figure 1, comprises the following steps:
a: firstly, growing a hole transport layer on an anode substrate;
b: then depositing a quantum dot light-emitting layer on the hole transport layer;
c: finally, an EDTA-2Na layer and an electron transport layer are sequentially deposited on the quantum dot light-emitting layer, and the EDTA-2Na layer and the electron transport layer are laminated and prepared according to the method in the embodiment 3;
d: and evaporating a cathode on the electron transmission layer to obtain the quantum dot light-emitting diode.
The QLED device of the present embodiment is of an upright configuration, and as shown in fig. 1, the QLED device includes, in order from bottom to top, a substrate 1, an anode 2, a hole transport layer 3, a quantum dot light emitting layer 4, an EDTA-2Na layer 5, an electron transport layer 6, and a cathode 7. The material of the substrate 1 is a glass sheet, the material of the anode 2 is an ITO substrate, the material of the hole transport layer 3 is TFB, the material of the quantum dot light-emitting layer 4 is quantum dots, the material of the EDTA-2Na layer 5 is EDTA-2Na, the material of the ZnS nanoparticles of the electron transport layer 5 and the material of the cathode 6 are Al.
Comparative example 1
A quantum dot light-emitting diode comprises a laminated structure of an anode and a cathode which are oppositely arranged, a quantum dot light-emitting layer arranged between the anode and the cathode, an electron transport layer arranged between the cathode and the quantum dot light-emitting layer, and a hole transport layer arranged between the anode and the quantum dot light-emitting layer, wherein the anode is arranged on a substrate. The substrate is made of a glass sheet, the anode is made of an ITO (indium tin oxide) substrate, the hole transport layer is made of TFB (thin film transistor), the electron transport layer is made of ZnO nano materials, and the cathode is made of Al.
And (3) performance testing:
the thin films of the laminated structure of the EDTA-2Na layer and the electron transport layer prepared in the examples 1 to 3, the electron transport layer prepared in the comparative example 1, the quantum dot light-emitting diodes prepared in the examples 4 and 5 and the comparative example 1 were subjected to performance tests, and the test indexes and the test method are as follows:
(1) Electron mobility: the electron transport film was tested for current density (J) -voltage (V), plotted as a graph, fitted to the Space Charge Limited Current (SCLC) region in the graph, and then calculated for electron mobility according to the well-known Child's law equation:
J＝(9/8)ε r ε 0 μ e V 2 /d 3
wherein J represents current density in mAcm -2 ；ε r Denotes the relative dielectric constant,. Epsilon 0 Represents the vacuum dielectric constant; mu.s e Denotes the electron mobility in cm 2 V -1 s -1 (ii) a V represents the drive voltage, in units of V; d represents the film thickness in m.
(2) Resistivity: and measuring the resistivity of the electronic transmission film by using the same resistivity measuring instrument.
(3) External Quantum Efficiency (EQE): measured using an EQE optical test instrument.
Note: the electron mobility and resistivity were tested as single layer thin film structure devices, namely: cathode/electron transport film/anode. The external quantum efficiency test is the QLED device, namely: anode/hole transport film/quantum dot/electron transport film/cathode.
The test results are shown in table 1 below:
TABLE 1
Figure BDA0002160452020000141
As can be seen from table 1 above, examples 1 to 3 of the present invention provided materials having an EDTA-2Na layer/metal compound electron transport layer laminate structure, the resistivity was significantly lower than that of the electron transport film prepared in comparative example 1, and the electron mobility was significantly higher than that of the electron transport film prepared in comparative example 1.
The external quantum efficiency of the quantum dot light-emitting diode (electron transport layer material is an EDTA-2Na layer/metal compound electron transport layer laminated structure) provided in embodiments 4 and 5 of the present invention is significantly higher than that of the quantum dot light-emitting diode in comparative example 1, which indicates that the quantum dot light-emitting diode obtained in the embodiments has better light-emitting efficiency.
It is noted that the embodiments provided by the present invention all use blue light quantum dots Cd X Zn 1-X S/ZnS is used as a quantum dot light-emitting layer material, is based on a blue light-emitting system, is a system which is used more (the blue light quantum dot light-emitting diode is difficult to achieve high efficiency, so the blue light quantum dot light-emitting diode has higher reference value), and does not represent that the invention is only used for the blue light-emitting system.
The above description is intended to be illustrative of the preferred embodiment of the present invention and should not be taken as limiting the invention, but rather, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Claims (6)

1. A quantum dot light-emitting diode is an upright quantum dot light-emitting diode and comprises an anode, a cathode and a quantum dot light-emitting layer positioned between the anode and the cathode, wherein an electron transmission layer is arranged between the cathode and the quantum dot light-emitting layer; and the ethylene diamine tetraacetic acid material on the surface of the electron transmission layer close to the quantum dot light-emitting layer forms an ethylene diamine tetraacetic acid disodium material layer.
2. The quantum dot light-emitting diode of claim 1, wherein the layer of disodium ethylenediaminetetraacetate material has a thickness of 20-60nm; and/or the presence of a gas in the gas,
the thickness of the electron transmission layer is 20-60nm; and/or the presence of a gas in the gas,
the material of the electron transport layer is selected from ZnO, znS and TiO 2 、SnO 2 、Ta 2 O 3 And ZrO 2 At least one of (1).
3. The qd-led of any one of claims 1-2, wherein an electron injection layer is disposed between the electron transport layer and the cathode; and/or the presence of a gas in the gas,
and a hole function layer is arranged between the quantum dot light-emitting layer and the anode.
4. A preparation method of a quantum dot light-emitting diode comprises the following steps:
providing an anode substrate;
preparing a quantum dot light emitting layer on the anode substrate;
preparing an ethylene diamine tetraacetic acid disodium material on the surface of the quantum dot light-emitting layer;
preparing an electron transport layer on the surface of the ethylene diamine tetraacetic acid material;
preparing a cathode on the electron transport layer;
and the ethylene diamine tetraacetic acid material on the surface of the electron transmission layer close to the quantum dot light-emitting layer forms an ethylene diamine tetraacetic acid disodium material layer.
5. The method of claim 4, wherein the step of preparing the disodium ethylene diamine tetraacetate material on the surface of the quantum dot light-emitting layer comprises: and preparing a disodium ethylene diamine tetraacetate solution, depositing the disodium ethylene diamine tetraacetate solution on the surface of the quantum dot light-emitting layer, and then carrying out annealing treatment.
6. The method for preparing a quantum dot light-emitting diode according to claim 5, wherein the solvent in the disodium ethylene diamine tetraacetate solution is at least one selected from methanol, ethanol, isopropanol and dimethyl sulfoxide; and/or the presence of a gas in the gas,
the concentration of the ethylene diamine tetraacetic acid in the ethylene diamine tetraacetic acid disodium solution is 10-20mg/ml; and/or the presence of a gas in the atmosphere,
the temperature of the annealing treatment is 100-150 ℃; and/or the presence of a gas in the gas,
the time of the annealing treatment is 10-20min.
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