CN114039002A

CN114039002A - Electron transport ink, electron transport film, electroluminescent diode, and display device

Info

Publication number: CN114039002A
Application number: CN202011476226.0A
Authority: CN
Inventors: 罗健; 庄锦勇
Original assignee: Guangdong Juhua Printing Display Technology Co Ltd
Current assignee: Guangdong Juhua Printing Display Technology Co Ltd
Priority date: 2020-12-15
Filing date: 2020-12-15
Publication date: 2022-02-11
Anticipated expiration: 2040-12-15
Also published as: CN114039002B

Abstract

The invention discloses an electron transfer ink, an electron transfer layer, an electroluminescent diode and a display device. The electron transport ink comprises a dispersing agent and a dispersoid dispersed in the dispersing agent, wherein the dispersoid comprises a first electron transport material and a second electron transport material, the first electron transport material and the second electron transport material are both selected from nanoparticles of materials with electron transport capacity, the particle size of the second electron transport material is 20 nm-100 nm, and the particle size ratio of the first electron transport material to the second electron transport material is (0.05-0.15): 1. The electron transmission film prepared by the electron transmission ink is more compact, can effectively inhibit the generation of leakage current, and improves the current efficiency of devices. In addition, the electron transmission film can also play a role in balancing current carriers in the electroluminescent diode, and the luminous efficiency of the device is improved.

Description

Electron transport ink, electron transport film, electroluminescent diode, and display device

Technical Field

The invention relates to the technical field of electronic display, in particular to an electronic transmission ink, an electronic transmission film, an electroluminescent diode and a display device.

Background

The organic light emitting diode and the quantum dot light emitting diode have the advantages of high color gamut, self-luminescence, low starting voltage, and fast response speed, and are considered to be the electroluminescent diodes with the most application prospect, and have been widely used in display devices.

A conventional multilayer electroluminescent diode device structure typically includes a cathode, an electron transport layer, a light emitting layer, a hole transport layer, and an anode. Wherein each layer can be prepared by magnetron sputtering, chemical vapor deposition and the like. However, these methods have some disadvantages. For example, in the magnetron sputtering process, the preparation process of the target is complicated, the utilization rate of the target is low, and if the utilization rate of the target is increased, the equipment cost is increased. In the chemical vapor deposition process, the reaction source participating in deposition and the gas after reaction are often flammable, explosive or toxic, and environmental protection measures need to be taken. The solution method preparation technology such as ink-jet printing is taken as a non-contact and dot-matrix printing technology which is gradually developed in recent years, can realize accurate quantification and positioning deposition of functional materials, has simpler process technology, does not need particularly strict environmental requirements, has lower manufacturing cost, can reduce pollution to the environment and waste of raw materials, and is an ideal preparation method suitable for large-scale production.

However, compared with electron transport layers prepared by magnetron sputtering and chemical vapor deposition methods, the electron transport layers prepared by solution methods such as inkjet printing have significantly poorer performance. In particular, such electron transport layers, when applied in quantum dot light emitting diodes, can cause device leakage current. In addition, in the conventional quantum dot light emitting diode, since the electron injection capability into the quantum dot light emitting layer is strong, the number of electrons in the quantum dot light emitting layer is usually much greater than that of holes, and the imbalance of carriers also causes the reduction of the light emitting performance and the life performance of the quantum dot light emitting diode.

Disclosure of Invention

In view of the above, an object of the present invention is to provide an electron transport ink capable of alleviating a leakage current of an electron transport layer and improving light emitting performance and life performance of a quantum dot light emitting diode.

It is a further object of the present invention to provide an electron transport film prepared from the electron transport ink, and a laminated light emitting diode and display device.

According to one embodiment of the invention, the electron transport ink comprises a dispersant and a dispersoid dispersed in the dispersant, wherein the dispersoid comprises a first electron transport material and a second electron transport material, the first electron transport material and the second electron transport material are both selected from nanoparticles of materials with electron transport capability, the particle size of the second electron transport material is 20 nm-100 nm, and the particle size ratio of the first electron transport material to the second electron transport material is (0.05-0.15): 1.

In one embodiment, the material with electron transport capability is a zinc oxide based material.

In one embodiment, the zinc oxide-based material is selected from ZnO, ZnMgO, ZnTiO₃、ZnMgTiO₃、ZnTiO₃、ZnCdO、ZnWO₄、ZnAlO、ZnNiO、ZnSnO₃And one or more of ZnTiSnO.

In one embodiment, the dispersant is selected from alcoholic solvents.

In one embodiment, the alcoholic solvent is selected from one or more of methanol, ethanol, isopropanol, butanol, glycerol, ethylene glycol, polyethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and pentylene glycol.

In one embodiment, the mass ratio of the dispersoid is 1 to 20% and the mass ratio of the dispersant is 80 to 99% in the electron transport ink.

In one embodiment, the first electron transport material is spherical; and/or the presence of a gas in the gas,

the second electron transport material is spherical; and/or the presence of a gas in the gas,

the mass ratio of the first electron transmission material to the second electron transmission material is 1 (5-100).

An electron transport film formed from the electron transport ink according to any of the above embodiments without a dispersant.

Further, an electroluminescent diode comprises a cathode, an anode, a light emitting layer arranged between the cathode and the anode in a laminating mode, and an electron transport layer arranged between the cathode and the light emitting layer in a laminating mode, wherein the electron transport layer is formed by removing a dispersing agent from the electron transport ink according to any one of the embodiments.

In one embodiment, the light emitting layer is a quantum dot light emitting layer.

And a display device comprising a driving element and a pixelated electroluminescent diode, the driving element being electrically connected to the electroluminescent diode for driving light emission of the electroluminescent diode, the electroluminescent diode being as described in any of the above embodiments.

The electrical property and compactness of the electron transport layer are the key to influence the film quality, while the ink prepared by the solution method is the key to prepare the electron transport layer, and the dispersoid in the traditional electron transport layer ink is mostly a nano-particle material with a single particle size. The inventors have found that electron transport layers prepared from such inks tend to suffer from leakage currents. This is because, on the one hand, the film is formed by stacking a plurality of particles in actual film formation due to the limitations of the solution process and the raw materials used, and the contact between the particles in such a film cannot be very dense and has a certain number of pores. On the other hand, the nanoparticle material in the ink is generally a nearly spherical or spherical nanoparticle, and even if it is deposited in a close-packed manner at the time of film formation, a certain gap still exists therein. These factors lead to the final formation of a less dense film, which may also lead to leakage current problems. In addition, in practical application, the quantum dot light emitting diode has the problems of strong electron injection capability and high electron mobility, which affects carrier balance in the quantum dot light emitting diode and limits the light emitting performance and service life of the device.

Based on the problems, the dispersoid comprises a first electron transport material and a second electron transport material, and the ratio of the particle sizes of the first electron transport material and the second electron transport material is (0.05-0.15): 1. Through the selection of the electron transmission materials with large particle size and small particle size, when the film is formed through deposition, the second electron transmission material with larger particle size can form a main body material of the film, and the first electron transmission material can be filled in gaps of the second electron transmission material, so that the prepared film is more compact. The more compact film has better electrical property, so that the generation of leakage current can be effectively inhibited, and the current efficiency of the device can be improved when the film is applied to the device. In addition, the electron mobility of the nano material with smaller particle size is lower than that of the nano material with larger particle size, and the nano material with larger particle size and the nano material with smaller particle size are simultaneously contained in the electron transfer ink, so that the electron mobility of the film prepared from the nano material can be reduced by mixing and matching the nano materials with different particle sizes. Therefore, the electron transport layer prepared by the electron transport ink can also play a role in balancing current carriers, and the luminous efficiency of the device is improved.

Drawings

FIG. 1 is a schematic structural diagram of an electroluminescent diode 10 according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a theoretical stacking structure of a first electron transport material and a second electron transport material.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. "Multi", as used herein, means a combination of two or more items. Unless explicitly indicated or otherwise generally understood by those skilled in the art, the ratios or concentrations in this application are to be considered mass ratios or mass concentrations.

The electrical property and compactness of the electron transport layer are key to influence the film quality, and the ink prepared by the solution method is key to prepare the electron transport layer. The ink generally includes a dispersant and an electron transport layer material dispersed in the dispersant, and the electron transport layer material may be an organic small molecule material, a polymer material or an inorganic material having an electron conduction capability. The inorganic material is typically nanoparticles, which are capable of being uniformly dispersed in a dispersant to form an ink, but do not dissolve. Therefore, the film made of the material is still composed of the original nanoparticles.

The dispersoids in conventional electron transport layer inks are mostly composed of nanoparticles of a single particle size or of a particle size that slightly fluctuates in a certain small range. After the quantum dot ink is formed on a substrate by a certain method, the dispersing agent is removed, and particles in the dispersing agent are stacked to form a film. In the film forming process, on one hand, due to the limitations of the solution method preparation process and the used raw materials, a film is formed by stacking a plurality of particles in the actual film forming process, the contact among the particles in the film cannot be very dense, and certain holes exist. On the other hand, the nanoparticle material in the ink is generally a nearly spherical or spherical nanoparticle, and even if it is deposited in a close-packed manner at the time of film formation, a certain gap still exists therein. These factors lead to the final formation of a less dense film, which may also lead to leakage current problems.

In view of the above problems, an embodiment of the present invention provides an electron transport ink capable of better solving the problem, and the electron transport ink can be applied to a method for preparing a thin film by a solution method, such as inkjet printing, spin coating, or pad printing, to prepare a dense thin film, so as to improve the problems of leakage current and carrier imbalance.

According to one embodiment of the invention, the electron transport ink comprises a dispersing agent and a dispersoid dispersed in the dispersing agent, wherein the dispersoid comprises a first electron transport material and a second electron transport material, the first electron transport material and the second electron transport material are selected from nanoparticles of materials with electron transport capability, and the ratio of the particle size of the first electron transport material to the particle size of the second electron transport material is (0.05-0.15): 1. The specific configuration of the electronic transfer ink that is optional is shown below by a number of different examples.

In one specific example, the mass ratio of the first electron transport material to the second electron transport material is 1 (5-100). In the particle size ratio, the first electron transport material and the second electron transport material with a specific mass ratio are selected, so that the amounts of the first electron transport material and the second electron transport material can be reasonably matched, and a more compact and uniform film is formed.

In one specific example, both the first electron transport material and the second electron transport material are insoluble in the dispersant, and maintain their original forms in the dispersant. Wherein "nanoparticles" refers to particles that are nanoscale in all three dimensions. The shape of the particles may be spindle, rod, sphere, or ellipsoid. Optionally, the first electron transport material is a spherical nanoparticle and/or the second electron transport material is a spherical nanoparticle. The "spherical" quantum dot material is not necessarily a perfect regular sphere, but may have an error in diameter in each direction, and the overall shape is close to that of a regular sphere. And the surface of the quantum dot material may be non-smooth, e.g. having suitable topographical defects.

In one specific example, the material having an electron transport ability may be selected from N-type metal chalcogenides, such as ZnS-based materials or ZnO-based materials. The N-type metal chalcogenide compound has stronger electron transport capability.

In one specific example, the nanoparticles with electron transport capability in the electron transport ink are particulate zinc oxide-based nanomaterials. The zinc oxide-based nanomaterial refers to zinc oxide or a derivative of zinc oxide formed after doping certain metal elements. Zinc oxide (ZnO) is a typical ii-vi wide bandgap direct semiconductor. Its forbidden band width is about 3.37eV at room temperature. The zinc oxide-based film doped with metal ions is a typical functional oxide material, has good optical, piezoelectric and gas-sensitive characteristics, and is widely applied to the fields of solar cells, high-power resistors, gas-sensitive sensors and the like. The zinc oxide-based nano material is a typical inorganic material with strong electron transport capability, and the electron transport capability of the zinc oxide-based nano material is far higher than that of most of the existing materials with hole transport capability, so that the quantum dot light-emitting diode using the zinc oxide-based nano material as an electron transport layer has the problem of obvious carrier imbalance.

In one specific example, the zinc oxide-based nanomaterial is selected from ZnO, ZnMgO, ZnTiO₃、ZnMgTiO₃、ZnTiO₃、ZnCdO、ZnWO₄、ZnAlO、ZnNiO、ZnSnO₃And one or more of ZnTiSnO. Wherein, like "ZnMgO" is commonly referred to as magnesium-doped zinc oxide, the chemical formula does not strictly represent the actual atomic composition, and other similar chemical formulas should be understood according to the general knowledge of those skilled in the art.

In one specific example, the dispersant is selected from alcohol solvents. The uniformity of dispersion of the dispersoids in the dispersant also significantly affects the properties of the film prepared from the electron transport ink. If the dispersoid cannot be uniformly dispersed, the components in the dispersoid are subjected to phase separation or have a phase separation tendency in the electron transport ink, and further, the first electron transport material with smaller particle size cannot be uniformly dispersed into gaps of the second electron transport material in the actual preparation process, so that the compactness of the prepared film is influenced. The first electron transport material and the second electron transport material can be uniformly dispersed in the alcohol solvent, so that the film prepared from the composite film water can obtain better compactness.

Moreover, in the actual preparation process, the material of the quantum dot light-emitting layer is usually prepared by using an ink with an oily dispersant as a dispersant, so that the condition of cross dissolution can be avoided by selecting the dispersant for preparing the ink of the electron transport material as an alcohol solvent.

In one specific example, the alcohol solvent is selected from one or more of methanol, ethanol, isopropanol, butanol, glycerol, ethylene glycol, polyethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and pentylene glycol.

Further, the alcohol solvent may be selected from one or more of isopropyl alcohol, propyl alcohol and glycerin, taking into consideration the viscosity and universality of the ink.

In one specific example, in the electron transport ink, the mass ratio of the dispersoid is 1% to 20%, and the mass ratio of the dispersant is 80% to 99%. For example, the mass ratio of the dispersant is 80%, 85%, 88%, 90%, 92%, 95%, 97%, 99% or a range between the above mass ratios. Correspondingly, the mass fraction of the dispersoid is 20%, 15%, 12%, 10%, 8%, 5%, 3%, 1% or a range between the above mass fractions. Only the dispersant and the dispersoid may be contained in the electron transport ink. Further, in the present embodiment, only the first electron transporting material and the second electron transporting material may be included in the dispersoid; in other embodiments, however, other materials may be included in the dispersoid, such as additives that may be used to improve the compatibility of the first electron transport material and the second electron transport material.

In one specific example, in the dispersoid, the mass ratio of the first electron transport material to the second electron transport material is optionally 1:5, 1:10, 1:20, 1:30, 1:40, 1:50, 1:60, 1:70, 1:80, 1:90, 1:100 or a range between the above mass ratios. By selecting a proper mass ratio, the compactness of the prepared film can be regulated and controlled, and the electron transmission performance of the prepared film can be regulated and controlled. Specifically, the introduction of the first electron transport material having a smaller particle size into the electron transport layer causes more interfaces in the thin film, the transport of electrons at the interfaces is greatly hindered, and the electron transport performance on the first electron transport material having a smaller particle size is also poor, which collectively play a role in reducing the electron transport efficiency in the electron transport layer.

In one specific example, the second electron transport material has a large particle size of 20nm to 100 nm. Optionally, the second electron transport material has a particle size of 20nm, 30nm, 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or a range therebetween. In particular, the particle size of the second electron transport material is 20nm to 50 nm.

In order to facilitate understanding of the advantages of the electronic transmission ink of the above embodiments of the present invention, a specific application scenario of the electronic transmission ink is described below.

Referring to fig. 1, a quantum dot light emitting diode 10 according to another embodiment of the present invention is provided. The quantum dot light emitting diode 10 includes an anode 110, a hole injection layer 120 stacked on the anode 110, a hole transport layer 130 stacked on the hole injection layer 120, a quantum dot light emitting layer 140 stacked on the hole transport layer 130, an electron transport layer 150 stacked on the quantum dot light emitting layer 140, and a cathode 160 stacked on the electron transport layer 150. It is understood that the hole transport layer 130, the hole injection layer 120, and the electron transport layer 150, among others, function to enhance the ability to inject holes and the ability to inject electrons into the light emitting layer 140, respectively.

Fig. 1 shows a quantum dot light emitting diode with a bottom emission structure, light exiting from a bottom anode 110. In one specific example, the anode 110 may be made of a light-transmissive material, wherein the light-transmissive material may be selected from: one or more of conductive metal oxides (e.g., ITO), graphene, carbon nanotubes, and conductive polymers. In the actual manufacturing process, the anode 110 may be usually attached to a substrate in advance, and the substrate may be selected from sapphire, glass, and the like. For example, a conductive metal oxide previously attached to a glass substrate is used as the anode 110.

In one specific example, the cathode 160 may be made of metal, and specifically, the cathode 160 may be selected from one or more of aluminum (Al), silver (Ag), and gold (Au). For a bottom emission structure, the thickness of the cathode 160 may be thicker to enhance reflectivity. For example, the thickness of the cathode may be 100nm to 200 nm.

In other specific examples, the above-mentioned qd-led 10 may also be a top emission structure, i.e. light is emitted from the top electrodeThe cathode 160 exits. At this time, the material of the anode 110 may be selected to have a sandwich electrode having an oxide/metal/oxide structure, in which oxides such as: conductive metal oxide (e.g., ITO), Indium Zinc Oxide (IZO), tungsten oxide (WO)₃) And molybdenum oxide (MoO)₃) Metal such as: one or more of gold (Au) and silver (Ag). The material of the cathode 160 can be selected from light-transmitting materials such as: one or more of a conductive metal oxide (e.g., ITO), a metal complex (e.g., Mg/Ag complex), and a high work function metal (e.g., Ag).

In one specific example, the material of the hole transport layer 130 is selected from materials having a hole transport capability, such as: one or more of a small molecule material, a polymeric material, and an inorganic material. Specifically, the small molecule material can be selected from aromatic diamine materials, such as TPD, NPB and the like; the polymer material can be selected from PEDOT, PSS, and the inorganic metal oxide can be selected from NiO. The thickness of the hole transport layer 130 may be 20nm to 50 nm. In particular, the thickness of the hole transport layer 130 may be 30nm to 40 nm.

It can be understood that the electron transport layer and the hole transport layer are used for promoting the injection of electrons and holes into the quantum dot light emitting layer, and are a more optional specific implementation scheme. However, the light emitting diode in some other specific examples may not have an electron transport layer and a hole transport layer. For example, the electroluminescent diode in other embodiments may include only a cathode, an anode, a light-emitting layer stacked between the cathode and the anode, and an electron transport layer stacked between the cathode and the light-emitting layer. Alternatively, in the electroluminescent diode of other embodiments, an electron injection layer may be additionally disposed between the cathode 160 and the electron transport layer 150 on the basis of the electroluminescent diode 10.

In one specific example, the material of the hole injection layer 120 may be selected from PEDOT: PSS (poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonic acid)). The thickness of the hole injection layer 120 may be 20nm to 60 nm. In particular, the thickness of the hole injection layer 120 may be 30nm to 50 nm.

In the electroluminescent diode 10, the electron transport layer 150 is a thin film formed by stacking two kinds of nanoparticles having different particle diameters. The thin film may be formed by removing the dispersant from the ink including the two types of nanoparticles having different particle diameters after the ink is formed on the surface of the light emitting layer 140. Specifically, the preparation method of the electron transport layer may include the steps of:

forming ink on a substrate material by a solution method, then removing a dispersing agent by a heating and drying method, and simultaneously annealing the nano material film. The annealing treatment can reduce the integral free energy of the film to a certain extent, reconstruct the crystal structure of the nano material, eliminate partial defects in the nano material, ensure that all the nano materials are combined more tightly and improve the electrical property of the film.

Among them, the solution method may be selected from inkjet printing or spin coating. The drying temperature can be controlled to be 100-150 ℃ when the temperature is raised and the drying is carried out. The drying time can be 5min to 30 min.

The ink for preparing the electron transport layer 150 is the electron transport ink in the above-described embodiment and each specific example thereof.

In one specific example, the thickness of the electron transport layer 150 may be 40nm to 100nm corresponding to the particle size of the second electron transport material. Specifically, the thickness of the electron transport layer 150 may be 40nm, 50nm, 60nm, 70nm, 80nm, 90nm, 100nm, or a range therebetween. Optionally, the thickness of the electron transport layer 150 is 50nm to 100 nm.

The electron transport layer 150 prepared from the above electron transport ink includes both the first electron transport material having a small particle size and the second electron transport material having a large particle size. When a film is formed by deposition, the second electron transport material with larger particle size can form a main body material of the film, and the first electron transport material can be filled in gaps of the second electron transport material, so that the prepared film is more compact. To facilitate an intuitive understanding of the electron transport layer 150 of the present invention, please refer to the contents shown in fig. 2. One preferred situation is: the three regular spherical second electron transport materials 152 with larger particle size form a close packing, and the spherical first electron transport materials 151 with smaller particle size are embedded in the gaps between the second electron transport materials 152, so that the ratio of the particle size of the first electron transport material 151 to the particle size of the second electron transport material 152 is about 0.077: 1. The actual preparation condition is more complex, so that the effect of improving the electrical property of the film can be achieved by setting the particle size within a certain range. The more compact film has better electrical property, thereby effectively inhibiting the generation of leakage current and improving the current efficiency of the device. In addition, the electron mobility of the nano-particles with smaller particle size is lower than that of the nano-materials with larger particle size, and more interfaces are introduced into the film by the nano-particles with smaller particle size, so that the electron mobility of the film prepared by the nano-particles with smaller particle size can be reduced by mixing and matching the nano-materials with different particle sizes. Therefore, the electron transport layer prepared by the electron transport ink can also play a role in balancing current carriers, and the luminous efficiency of the device is improved.

Another embodiment of the present invention provides a method for manufacturing the quantum dot light emitting diode 10, which includes the following steps:

providing a substrate coated with an anode thin film, such as a glass substrate and an ITO anode laminated on the glass substrate;

an ink containing a hole injection layer material, such as PEDOT: PSS, is spin coated on the substrate. Alternatively, the spin speed is 2000r/min, and the spin time is 40 s. After completion of the spin coating, annealing was performed at 150 ℃ for 15min to prepare a hole injection layer.

An ink containing a hole transport layer material, such as a chlorobenzene solution of TFB, is spin coated over the hole injection layer. Alternatively, the spin speed is 3000r/min, and the spin time is 40 s. After the completion of spin coating, annealing was performed at 150 ℃ for 30min to prepare a hole transport layer.

An ink containing a quantum dot emissive material, such as CdSe/ZnS red quantum dots, is spin coated over the hole transport layer. Alternatively, the spin speed is 3000r/min, and the spin time is 40 s. And annealing at 120 ℃ for 10min after the spin coating is finished to prepare the quantum dot light-emitting layer. The quantum dot light emitting layer is only a red light quantum dot light emitting layer, and in other specific examples, green quantum dots or blue quantum dots can be correspondingly selected to prepare a green light quantum dot light emitting layer or a blue light quantum dot light emitting layer.

The electron transport ink provided by the above embodiment of the invention is spin-coated on the quantum dot light emitting layer. Alternatively, the spin speed is 3000r/min, and the spin time is 40 s. After the completion of spin coating, annealing was performed at 120 ℃ for 10min to prepare an electron transport layer.

On the electron transport layer, under high vacuum (10)^-7Torr) was used to deposit a silver cathode layer having a thickness of about 150 nm.

It will be appreciated that the thicknesses set forth in the above examples are approximate and that in actual fabrication processes, the thicknesses produced will often be subject to some error, but overall similar performance can be achieved.

On the other hand, a further embodiment of the present invention also provides a display device, which includes a driving element and a pixelized electroluminescent diode, the driving element is electrically connected with the electroluminescent diode for driving the light emission of the electroluminescent diode, and the electroluminescent diode is the quantum dot light-emitting diode 10 in the above embodiment.

It is understood that the quantum dot light emitting diode 10 of the above embodiment is only one application scenario of the electron transport ink, and does not represent that the electron transport ink and the thin film prepared therefrom are only applicable to the scenario, and the composite film or the thin film prepared therefrom can also be applied to many other scenarios.

For example, the electron transport ink including a zinc oxide-based material may also be applied in solar cells, high power resistors, and gas sensors due to the unique semiconductor properties of the zinc oxide-based material.

Specific, alternative examples and comparative examples are provided below to facilitate understanding and practice of the invention. The technical solution of the present invention will be more apparent and the advantages thereof will be more apparent from the examples and comparative examples.

The materials used in the examples and comparative examples are all commercially available in the ordinary course of practice, unless otherwise specified.

Example 1

While stirring, 1g of ZnO spherical nanoparticles having a particle size of about 20nm, 0.01g of ZnO spherical nanoparticles having a particle size of about 3nm, 50g of glycerol, and 10g of isopropanol solvent were sequentially added to a 100mL round-bottom flask, and the mixture was stirred for another 30 minutes to be uniformly dispersed without coagulation, thereby obtaining ZnO ink.

Example 2

While stirring, 1g of ZnMgO spherical nanoparticles with the particle size of about 30nm, 0.02g of ZnMgO nanoparticles with the particle size of about 4nm, 50g of glycerol and 10g of isopropanol solvent are sequentially added into a 100mL round-bottom flask, and the mixture is stirred for 30 minutes to be uniformly dispersed without coagulation, so that ZnMgO ink is obtained.

Example 3

Under the condition of stirring, 1g of ZnO spherical nano-particles with the particle size of about 50nm, 0.1g of ZnMgO spherical nano-particles with the particle size of about 5nm, 50g of glycerol and 10g of isopropanol solvent are sequentially added into a 100mL round-bottom flask, and the mixture is stirred for 30 minutes continuously to be uniformly dispersed without coagulation, so that ZnO/ZnMgO ink is obtained.

Example 4

Under the condition of stirring, 1g of ZnO spherical nano-particles with the particle size of about 100nm, 0.2g of ZnMgO spherical nano-particles with the particle size of about 5nm, 50g of glycerol and 10g of isopropanol solvent are sequentially added into a 100mL round-bottom flask, and the mixture is stirred for 30 minutes continuously to be uniformly dispersed without coagulation, so that ZnO/ZnMgO ink is obtained.

Comparative example 1

While stirring, 1.01g of ZnO spherical nanoparticles having a particle size of about 20nm, 50g of glycerol, and 10g of isopropanol solvent were sequentially added to a 100mL round-bottom flask, and the mixture was stirred for another 30 minutes to be uniformly dispersed without coagulation, thereby obtaining a ZnO ink.

Comparative example 2

While stirring, 1g of ZnO spherical nanoparticles with a particle size of about 20nm, 0.5g of ZnO spherical nanoparticles with a particle size of about 3nm, 50g of glycerol and 10g of isopropanol solvent were added in sequence to a 100mL round-bottom flask, and the mixture was stirred for another 30 minutes to be uniformly dispersed without coagulation, thereby obtaining ZnO ink.

Test example: the electron transport layers of the quantum dot light emitting diodes were prepared using the inks of the respective examples and comparative examples described above. The quantum dot light-emitting diodes are identical except for an electron transport layer, specifically, the substrate layer is a glass substrate, the ITO anode and the hole injection layer which are stacked on the glass substrate are made of poly (3, 4-ethylenedioxythiophene) -poly (styrenesulfonic acid) (PEDOT: PSS), the hole transport layer is made of poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (TFB), the quantum dot light-emitting layer is red light CdSe/ZnS, and the cathode layer is made of silver.

The preparation method comprises the following steps:

providing a glass substrate with ITO arranged in a laminated mode as a substrate layer;

PSS is spin-coated on the substrate layer, the spin-coating speed is 2000r/min, the spin-coating time is 40s, and then annealing is carried out for 15min at 150 ℃ to form a hole injection layer with the thickness of about 40 nm;

spin-coating a TFB chlorobenzene solution with the concentration of 10mg/ml on the hole injection layer, carrying out spin-coating at the rotating speed of 3000r/min for 40s, and then annealing at 150 ℃ for 30min to form a hole transport layer with the thickness of about 35 nm;

spin-coating 20mg/mL red light CdSe/ZnS red light quantum dot ink on the hole transport layer, wherein the spin-coating rotation speed is 3000r/min, the spin-coating time is 40s, annealing is carried out for 10min at 120 ℃, and a quantum dot light-emitting layer is formed and has the thickness of about 20 nm;

spin-coating the inks of the above embodiments and comparative examples on the quantum dot light emitting layer at a spin speed of 3000r/min for 40s, and annealing at 120 ℃ for 30min to form an electron transport layer with a thickness of about 100 nm;

finally in high vacuum (10)^-7Torr) was used to deposit a 150nm silver cathode layer.

The maximum external quantum efficiency and current efficiency of each quantum dot light emitting diode were tested separately, and the results can be seen in table 1.

TABLE 1

Item	Maximum external quantum efficiency	Maximum current efficiency (cd/A)
			Example 1	18.5％	20.8
Example 2	19.7％	22.2
			Example 3	20.9％	23.6
Example 4	19.1％	21.9
			Comparative example 1	11.3％	14.2
Comparative example 2	15.6％	16.8

For a quantum dot light emitting diode, the electroluminescent properties, such as maximum external quantum efficiency and maximum current efficiency, can visually reflect the ability of the light emitting diode to convert current into light. According to the data in table 1, it can be found that the maximum external quantum efficiency and the maximum current efficiency of the quantum dot light emitting diode device can be significantly improved compared with the quantum dot ink which only adopts the electron transport material with the larger particle size as the dispersoid, and the electron transport layer which is prepared by adopting the electron transport material with the larger particle size and the electron transport material with the smaller particle size as the dispersoid. Thus, the data demonstrate that electron transport materials with smaller particle sizes can be embedded in quantum dot thin films, increasing the density of the quantum dot thin films, thereby increasing the maximum current efficiency. Meanwhile, due to the fact that the electron transport material with the small particle size is added, the electron transfer performance of the electron transport layer is reduced, the number of current carriers is more balanced, and therefore the maximum external quantum efficiency can be further improved.

The technical features of the above embodiments can be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the above embodiments are not described, but should be considered as the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above examples are merely illustrative of one preferred embodiment of the present invention, which is described in more detail and detail, but should not be construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims

1. The electronic transmission ink is characterized by comprising a dispersant and a dispersoid dispersed in the dispersant, wherein the dispersoid comprises a first electronic transmission material and a second electronic transmission material, the first electronic transmission material and the second electronic transmission material are respectively selected from nanoparticles of materials with electronic transmission capability, the particle size of the second electronic transmission material is 20 nm-100 nm, and the particle size ratio of the first electronic transmission material to the second electronic transmission material is (0.05-0.15): 1.

2. The electron transport ink of claim 1, wherein the electron transport material is a zinc oxide based material.

3. The electron transport ink of claim 2, wherein the zinc oxide-based material is selected from the group consisting of ZnO, ZnMgO, ZnTiO₃、ZnMgTiO₃、ZnTiO₃、ZnCdO、ZnWO₄、ZnAlO、ZnNiO、ZnSnO₃And one or more of ZnTiSnO.

4. The electron transport ink of claim 1, wherein the dispersant is selected from alcohol solvents.

5. The electronic ink according to claim 4, wherein the alcohol solvent is one or more selected from methanol, ethanol, isopropanol, butanol, glycerol, ethylene glycol, polyethylene glycol, diethylene glycol, propylene glycol, butylene glycol, and pentylene glycol.

6. The electron transport ink according to any one of claims 1 to 5, wherein the dispersoid is 1 to 20% by mass and the dispersant is 80 to 99% by mass in the electron transport ink.

7. The electron transport ink of any one of claims 1 to 5, wherein the first electron transport material is spherical; and/or the presence of a gas in the gas,

8. An electron transport film formed by removing the dispersant from the electron transport ink according to any one of claims 1 to 7.

9. An electroluminescent diode comprising a cathode, an anode, a light-emitting layer laminated between the cathode and the anode, and an electron transport layer laminated between the cathode and the light-emitting layer, wherein the electron transport layer is the electron transport film according to claim 8.

10. A display device comprising a driving element and a pixelated electroluminescent diode, the driving element being electrically connected to the electroluminescent diode for driving light emission of the electroluminescent diode, the electroluminescent diode being as claimed in claim 9.