CN115537072B

CN115537072B - Quantum dot ink, quantum dot light emitting diode, preparation method of quantum dot ink and quantum dot light emitting diode, and display device

Info

Publication number: CN115537072B
Application number: CN202110727250.5A
Authority: CN
Inventors: 许冰
Original assignee: Guangdong Juhua Printing Display Technology Co Ltd
Current assignee: Guangdong Juhua Printing Display Technology Co Ltd
Priority date: 2021-06-29
Filing date: 2021-06-29
Publication date: 2024-04-02
Anticipated expiration: 2041-06-29
Also published as: CN115537072A

Abstract

The embodiment of the application provides quantum dot ink, a quantum dot light emitting diode, a preparation method of the quantum dot ink and the quantum dot light emitting diode, and a display device; the quantum dot ink comprises a doping agent of a first polar group and a first nonpolar group, wherein the first polar group can coordinate with a metal oxide, the first nonpolar group can be self-assembled into layers, the first polar group comprises at least one of phosphine groups, amine groups or phosphorus oxy groups, and the first nonpolar group comprises at least one of alkyl chains formed by 6 to 16 carbon atoms, aromatic groups or aromatic groups substituted by the alkyl chains; when the quantum dot ink is deposited on the surface of the electronic functional layer, the first polar group can generate coordination action with the surface of one side, far away from the substrate, of the electronic functional layer, meanwhile, the hydrophobic chain segment of the first nonpolar group forms a self-assembled insulating layer on the electronic functional layer, the insulating layer can passivate surface defects of the electronic functional layer, the effect of electron injection is weakened, and the luminous efficiency of the quantum dot light emitting diode is further improved.

Description

Quantum dot ink, quantum dot light emitting diode, preparation method of quantum dot ink and quantum dot light emitting diode, and display device

Technical Field

The application relates to the technical field of display, in particular to quantum dot ink, a quantum dot light emitting diode, a preparation method of the quantum dot ink and the quantum dot light emitting diode, and a display device.

Background

A self-luminous QLED (Quantum Dot Light-Emitting Diode) device using inorganic quantum dots as an electroluminescent material has advantages of wide color gamut coverage, high color purity, ultra-thin portability, bendable curling, and the like, and thus has received a wide attention in academic and industrial fields.

At present, in the process of preparing an inverted QLED device, a metal oxide nanocrystal is generally adopted as an electron injection layer or an electron transport layer, a quantum dot luminescent layer is formed on the surface of the electron injection layer or the electron transport layer by a solution method, then a hole transport layer and a hole injection layer are deposited by a vacuum evaporation mode, and finally an anode is formed. In the current device structure, defects on the surface of the metal oxide nanocrystals have quenching effect on quantum dot excitons, which results in a decrease in quantum yield of radiative transitions, resulting in a decrease in the luminous efficiency of the QLED device.

Therefore, it is necessary to develop a quantum dot ink, a quantum dot light emitting diode, a method for manufacturing the same, and a display device, so as to overcome the defects of the prior art.

Disclosure of Invention

The embodiment of the application provides quantum dot ink, a quantum dot light emitting diode, a preparation method thereof and a display device, which are used for solving the technical problem that the luminous efficiency of a QLED device is low due to the defect of the surface of an electronic functional layer.

The embodiment of the application provides a quantum dot ink, which comprises a doping agent, a quantum dot material and an organic solvent, wherein the doping agent comprises a first polar group and a first nonpolar group, the first polar group can coordinate with a metal oxide, the first nonpolar group can self-assemble into layers,

preferably, the first polar group includes at least one of a phosphine group, an amine group, or a phosphorus oxide group, and the first nonpolar group includes at least one of an alkyl chain composed of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with the alkyl chain.

Optionally, in some embodiments of the present application, the dopant has a molecular weight of less than 500.

Optionally, in some embodiments of the present application, the quantum dot material comprises a hydrophobic ligand,

the hydrophobic ligand is not less capable of coordinating to a metal than the first polar group in the dopant,

Preferably, the hydrophobic ligand comprises a second polar group and a second non-polar group,

still preferably, the second polar group includes at least one of a carboxyl group, a mercapto group, a phosphine group, or an amine group, and the second nonpolar group includes at least one of an alkyl chain composed of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with the alkyl chain.

Optionally, in some embodiments of the present application, the organic solvent has a melting point less than or equal to 0 ℃, a boiling point range of 100 ℃ to 300 ℃,

preferably, the organic solvent comprises a chain alkane, a cycloalkane, a haloalkane, an aromatic hydrocarbon, a chain alkane, a cycloalkane, a haloalkane, a derivative of an aromatic hydrocarbon, and combinations thereof.

Optionally, in some embodiments of the present application, the organic solvent is 79.8% to 98.97% by mass of the quantum dot material in the quantum dot ink, 1% to 20% by mass of the dopant in the quantum dot ink, and 0.03% to 0.2% by mass of the dopant in the quantum dot ink.

Optionally, in some embodiments of the present application, the mass ratio of the dopant to the quantum dot material ranges from 1% to 10%.

Correspondingly, the embodiment of the application also provides a quantum dot light-emitting diode, which comprises a light-emitting layer and an electronic functional layer, wherein the light-emitting layer is made of the quantum dot ink as described in any one of the above, and the electronic functional layer is made of metal oxide;

wherein, the first polar group in the quantum dot ink coordinates with the metal oxide, and the first nonpolar group in the quantum dot ink self-assembles into a layer on the surface of the metal oxide.

Optionally, in some embodiments of the present application, the metal oxide comprises at least one of zinc oxide, titanium dioxide, or tin dioxide.

Correspondingly, the embodiment of the application also provides a preparation method of the quantum dot light emitting diode, which comprises the following steps:

forming an electron function layer on the cathode layer;

forming a quantum dot composite layer on the electronic functional layer, wherein the quantum dot composite layer comprises an insulating layer formed on the electronic functional layer and a light-emitting layer formed on the insulating layer;

the step of forming the quantum dot composite layer comprises the following steps:

coating the quantum dot ink on the surface of the electronic functional layer; drying the quantum dot ink to form a quantum dot film;

And carrying out thermal annealing treatment on the quantum dot film to form the quantum dot composite layer.

Optionally, in some embodiments of the present application, the step of forming a quantum dot composite layer on the electronic functional layer further includes:

forming a hole transport layer on the quantum dot composite layer;

forming a hole injection layer on the hole transport layer;

an anode layer is formed on the hole injection layer.

Optionally, in some embodiments of the present application, the cathode layer is ITO, the electron-functional layer is zinc oxide nanocrystals, the hole-transporting layer is TCTA, and the hole-injecting layer is MoO ₃ The anode layer is silver metal. Correspondingly, the embodiment of the application also provides a display device which comprises the quantum dot light emitting diode or the quantum dot light emitting diode prepared by the preparation method of the quantum dot light emitting diode.

According to the quantum dot ink, the quantum dot light emitting diode, the preparation method thereof and the display device provided by the embodiment of the application, the doping agent containing the first polar group and the first nonpolar group is added into the quantum dot ink, the first polar group can coordinate with the metal oxide, the first nonpolar group can be self-assembled into layers, the first polar group comprises at least one of phosphine groups, amine groups or phosphorus oxide groups, and the first nonpolar group comprises at least one of alkyl chains formed by 6 to 16 carbon atoms, aromatic groups or aromatic groups substituted by the alkyl chains, wherein the first polar group has the metal oxide coordination ability similar to or weaker than that of a quantum dot material in the quantum dot ink, and the concentration of the doping agent in the quantum dot ink is lower, so that ligand exchange reaction does not occur between the doping agent and the hydrophobic ligand in the quantum dot ink, but the doping agent mainly exists in a dissolved and dispersed molecular form; when the equivalent quantum dot ink is deposited on the surface of the electronic functional layer, the first polar group can generate coordination action with the surface of one side, far away from the substrate, of the electronic functional layer and is attached to the electronic functional layer, meanwhile, the hydrophobic chain segment of the first nonpolar group forms a self-assembled insulating layer on the electronic functional layer, the insulating layer can passivate the surface defect of the electronic functional layer, further exciton quenching at the interface between the light-emitting layer and the electronic functional layer is inhibited, the effect of electron injection is further weakened, and the light-emitting efficiency of the quantum dot light-emitting diode is further improved.

Drawings

In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings that are needed in the description of the embodiments will be briefly introduced below, it being obvious that the drawings in the following description are only some embodiments of the present application, and that other drawings may be obtained according to these drawings without inventive effort for a person skilled in the art.

Fig. 1 is a schematic flow chart of a preparation method of quantum dot ink provided in an embodiment of the present application;

fig. 2 is a schematic structural diagram of a quantum dot light emitting device according to an embodiment of the present application;

fig. 3 is a schematic flow chart of a preparation method of a quantum dot light emitting device according to an embodiment of the present application.

Detailed Description

The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all, of the embodiments of the present application. All other embodiments, which can be made by those skilled in the art based on the embodiments herein without making any inventive effort, are intended to be within the scope of the present application.

Embodiments of the present application provide a quantum dot ink comprising a dopant, a quantum dot material, and an organic solvent, the dopant package Includes a first polar group R ₁ And a first nonpolar group R ₂ The first polar group R ₁ Capable of coordinating to metal oxides, said first non-polar group R ₂ Capable of self-assembling into layers;

wherein the first polar group includes at least one of a phosphine group, an amine group, or a phosphorus oxide group, and the first nonpolar group includes at least one of an alkyl chain composed of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with the alkyl chain. The doping agent added in the quantum dot ink comprises a first polar group R ₁ And a first nonpolar group R ₂ A first polar group R ₁ Capable of complexing with metal oxides, a first non-polar group R ₂ The quantum dot ink can be self-assembled into layers, the first polar group comprises at least one of phosphine group, amine group or phosphorus oxide group, the first nonpolar group comprises at least one of alkyl chain, aromatic group or aromatic group substituted by alkyl chain which are formed by 6 to 16 carbon atoms, wherein the first polar group has metal oxide coordination ability similar to or weaker than that of a hydrophobic ligand of the quantum dot material, the metal oxide coordination ability can be attached to an electronic functional layer through coordination chemical bonds, the first nonpolar group is self-assembled into layers on the electronic functional layer, surface defects of the electronic functional layer can be passivated, exciton quenching at an interface between a light emitting layer and the electronic functional layer is further suppressed, the effect of electron injection is further weakened, and the luminous efficiency of a quantum dot light emitting diode prepared by using the quantum dot ink is further improved.

The technical solutions of the present application will now be described with reference to specific embodiments.

The embodiment of the application firstly provides a quantum dot ink, which comprises a dopant, a quantum dot material and an organic solvent, wherein the dopant comprises a first polar group R ₁ And a first nonpolar group R ₂ . The first polar group R ₁ Capable of coordinating to metal oxides, said first non-polar group R ₂ Capable of self-assembling into layers;

wherein the first polar group R ₁ Comprising at least one of a phosphine group, an amine group or a phosphorus oxide group, said first nonpolarGroup R ₂ Comprising at least one of an alkyl chain consisting of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with said alkyl chain.

Specifically, the molecular weight of the dopant is less than 500. If the molecular weight of the dopant is greater than or equal to 500, this will result in the first non-polar group R in the dopant ₂ The thickness of the insulating layer formed by self-assembly is too large, and the electron density injected into the light-emitting layer subsequently is influenced by the thickness of the insulating layer, so that the light-emitting efficiency of the QLED device manufactured subsequently is reduced.

Among them, self-assembly (self-assembly) refers to a technique in which basic structural units (molecules, nanomaterials, substances of micrometer or larger scale) spontaneously form an ordered structure. During self-assembly, the basic building blocks spontaneously organize or aggregate into a stable, regular geometric appearance under non-covalent based interactions.

In one embodiment of the present application, the dopant material comprises diphenylphosphine or diphenylphosphine chloride; wherein said diphenylphosphine or said diphenylphosphine chloride is commercially available.

In one embodiment of the present application, the dopant material comprises tri-n-octylphosphine, wherein the tri-n-octylphosphine is commercially available.

In one embodiment of the present application, the dopant material includes n-hexylamine, which has the chemical structural formula:

wherein said n-hexylamine is commercially available.

In one embodiment of the present application, the dopant material comprises 4-hexylaniline having the chemical formula:

wherein the 4-hexylaniline is commercially available.

In one embodiment of the present application, the dopant material comprises 4-hexyl chloroaniline; wherein the 4-hexyl chloroaniline is commercially available.

In one embodiment of the present application, the dopant material comprises tri-n-octylphosphorus oxide having the chemical structural formula:

wherein the tri-n-octyl phosphorus oxide is commercially available.

In one embodiment of the present application, the dopant material comprises diphenylphosphorus oxide, wherein the diphenylphosphorus oxide is commercially available. In one embodiment of the present application, the dopant material comprises a primary dodecylamine having the chemical formula:

Wherein the dodecylamine is commercially available.

In the above-described embodiments of the present application, the quantum dot material is a hydrophobic material, the quantum dot material includes a core-shell-ligand structure, and the quantum dot material is capable of forming a light emitting layer of a quantum dot light emitting device. The core-shell-ligand structure comprises a core layer quantum dot material, a shell layer quantum dot material and a hydrophobic ligand which are arranged from inside to outside.

In the above-described embodiments of the present application, the core layer quantum dot material includes a quantum dot composed of a semiconductor or perovskite, the semiconductor including a compound composed of an element in groups II and VI, a compound composed of an element in groups III and V, or a compound composed of an element in groups I, III, and VI; preferably, the core layer quantum dot material comprises an alloy of at least one or more of CdTe, cdSe, cdS, znTe, znSe, znS, inP, inAs, inSb, gaAs, gaP, gaSb, hgTe, hgSe, hgS, cuInS and CuInSe.

In the above-described embodiments of the present application, the shell quantum dot material also includes a quantum dot composed of a semiconductor including a compound composed of an element in groups II and VI, a compound composed of an element in groups III and V, or a compound composed of an element in groups I, III, and VI; preferably, the shell quantum dot material comprises an alloy of at least one or more of CdSe, cdS, znSe and ZnS.

In the above embodiments of the present application, the hydrophobic ligand has a ligand capacity to metal that is not greater than the first polar group R in the dopant ₁ Weak coordination ability with the metal, the structure of the hydrophobic ligand comprises a second polar group R ₃ A second nonpolar group R ₄ The second polar group R ₃ Comprises at least one of carboxyl, sulfhydryl, phosphino or amino;

wherein the second polar group R ₃ Is more capable of coordination than the first polar group R ₁ Is used as a ligand. Further, the second polar group R ₃ Is a polar group with a certain metal oxide coordination ability, which is stronger than or close to the first polar group R ₁ The second nonpolar group R ₄ Is a non-polar hydrophobic chain. Specifically, the second polar group R ₃ Comprises at least one of carboxyl, sulfhydryl, phosphino and amino; the second nonpolar group R ₄ Is a hydrophobic group, the second nonpolar group R ₄ Comprising at least one of an alkyl chain of 6 to 16 carbon atoms, an aromatic group, and an aromatic group substituted with the alkyl chain.

Because the surface of the quantum dot material is electrically neutral, the quantum dot material and the electronic transmission material oxadiazole are not easy to agglomerate. Therefore, the problem that the quantum dot material is dispersed in the quantum dot ink and the problem that the quantum dot material is easy to agglomerate with the electron transport material are solved by adopting the hydrophobic quantum dot material and the organic solvent.

In summary, by the above selection, the first polar group R of the dopant ₁ And the second polar group R in the hydrophobic ligand in the quantum dot material ₃ Compared with the prior art, the catalyst has similar or weaker coordination capability.

In the above-described embodiments of the present application, the organic solvent includes chain alkanes, cycloalkanes, haloalkanes, aromatic hydrocarbons, and derivatives of any of the foregoing, and combinations thereof; wherein the melting point of any one of the components in the organic solvent is less than or equal to 0 ℃, the organic solvent is liquid at normal temperature and the boiling point of the organic solvent is between 100 ℃ and 300 ℃ under normal pressure. Wherein, the melting point of any component in the organic solvent is less than or equal to more than 0 ℃ to ensure that the organic solvent is in a liquid state at normal temperature, and the doping agent and the quantum dot material can be better dissolved; the boiling point of the organic solvent is between 100 ℃ and 300 ℃ under normal pressure, so that the organic solvent can be prevented from bumping under the condition of reducing volatilization of the organic solvent. In the above embodiments of the present application, the mass percentage of the organic solvent in the quantum dot ink is 79.8% to 98.97%, the mass percentage of the quantum dot material in the quantum dot ink is 1% to 20%, and the mass percentage of the dopant in the quantum dot ink is 0.03% to 0.2%;

Wherein the mass ratio of the dopant to the quantum dot material is in the range of 0.01 to 0.1. If the mass percentage of the quantum dot material in the quantum dot ink is less than 1%, the thickness of the finally obtained luminescent layer is too thin, and the luminescent efficiency of the display panel is affected; if the mass percentage of the quantum dot material in the quantum dot ink is greater than 20%, the thickness of the finally obtained luminescent layer is too thick, and the luminescent efficiency of the display panel is affected.

Further, the self-assembled insulating layer has the following two beneficial effects: (1) Inhibiting exciton quenching at the interface between the electron injection/transport layer and the light-emitting layer, and improving quantum yield of exciton radiative transition; (2) The injection of electrons into the light-emitting layer is weakened, and the charge balance in the device is promoted, so that the efficiency of the QLED device can be improved on the premise of not introducing an additional functional layer deposition step.

Specifically, if the mass ratio of the dopant to the quantum dot material is in the range of less than 0.01, the thickness of the resulting insulating layer is too thin, and it is difficult to suppress the exciton quenching phenomenon generated between the surface of the electron functional layer and the quantum light emitting layer of the display panel; if the mass ratio of the dopant to the quantum dot material is in a range of more than 0.1, the concentration of the dopant in the quantum dot ink is too high, resulting in a ligand exchange reaction with the hydrophobic ligand in the quantum dot ink, thereby making it difficult to form an insulating layer and further suppressing the exciton quenching phenomenon generated between the surface of the electron functional layer and the quantum light emitting layer of the display panel.

The quantum dot ink in the embodiment of the present application is characterized by containing a small amount of dopant, and its molecular structure includes a polar group having a certain metal oxide coordination ability, and a nonpolar hydrophobic segment of alkyl or aryl group. The doping agent has similar or weaker coordination capability with the hydrophobic ligand in the quantum dot material, and the concentration of the doping agent in the quantum dot ink is lower, so that the doping agent does not undergo ligand exchange reaction with the hydrophobic ligand in the hydrophobic quantum dot material in the quantum dot ink, but exists mainly in a dissolved and dispersed molecular form.

In the above examples of the present application, the viscosity of the quantum dot ink is 2.5 to 10cP, and the surface tension is 32 to 42mN/m (mN/m is the surface tension coefficient of the liquid, which represents the mutual traction force per unit length between the adjacent two parts of the liquid surface; the first m in mN/m represents 10 to 3 and the latter m is the unit of meter, so mN/m=10 to 3*N/m, i.e., 0.001 newton/meter).

The viscosity and surface tension may be measured by methods commonly used in the art, for example, a capillary viscometer, a rotary viscometer, a vibrating viscometer, etc., and the surface tension may be measured by a rotary drop interfacial tensiometer, a microcomputer surface tensiometer, a hydrostatic surface tensiometer, etc. The test results of viscosity and surface tension are mainly related to temperature, but are not related to the adopted test method and test instrument. In the embodiment, the viscosity is measured by a digital display rotary viscometer, the liquid to be measured is injected into an instrument, and the measurement is started by clicking; in this embodiment, the surface tension is measured by using a rotary drop interfacial tension meter, tracking the moving drop by using a video optical system of the machine, acquiring and imaging by using a digital imaging system, and analyzing and measuring the image of the drop to calculate the surface tension value.

In the above embodiments of the present application, the quantum dot ink may be applied to high-end display applications such as QD-OLED or QD-Micro/Mini LED (quantum dot Micro/Mini light emitting diode) or PE-Micro/Mini LED (perovskite Micro/Mini light emitting diode).

Fig. 1 is a schematic flow chart of a preparation method of quantum dot ink according to an embodiment of the present application; wherein the method comprises the following steps:

s101, mixing a dopant with a first organic solvent to form a dopant preparation solution A, wherein the mass percentage of the dopant in the dopant preparation solution A is in the range of 0.5-10%.

Specifically, the S101 further includes:

firstly, providing a dopant and a first part of organic solvent, wherein the molecular weight of the dopant is less than 500, and the structure of the dopant is provided with a first polar group R ₁ A first nonpolar group R ₂ The method comprises the steps of carrying out a first treatment on the surface of the The first polar group R ₁ Is a polar group with certain metal oxide coordination ability, the first nonpolar group R ₂ Is a hydrophobic group; wherein the first polar group R ₁ Comprises at least one of phosphinyl, amino and phosphorus oxide; the first nonpolar group R ₂ Comprising at least one of an alkyl chain of 6 to 16 carbon atoms, an aromatic group, and an aromatic group substituted with the alkyl chain. The organic solvent comprises chain alkane, cycloalkane, halogenated alkane, aromatic hydrocarbon and derivatives and combinations thereof, namely the organic solvent comprises any one or two or more of the chain alkane, chain alkane derivatives, cycloalkane derivatives, halogenated alkane derivatives, aromatic hydrocarbon or aromatic hydrocarbon derivatives; further, the melting point of any component in the organic solvent is not more than 0 DEG C Boiling point is 100-300 deg.c.

In the above-described embodiments of the present application, the organic solvent includes at least one of octane, chlorooctane, o-xylene, m-xylene, phenylcyclohexane, methyl benzoate, toluene, chlorobenzene, and dichlorobenzene; alternatively, the organic solvent further includes a combination of o-xylene and phenylcyclohexane and a combination of phenylcyclohexane and methyl benzoate.

Specifically, the mixing mode is at least one selected from stirring, shaking and ultrasonic dispersing, and the mixing process can be accompanied by a certain degree of heating. The mixed solution or suspension has the characteristics of clarification and uniformity, and larger agglomerated particles are removed by a polytetrafluoroethylene filter membrane with a pore size of 0.2 microns or 0.45 microns before use.

S102, mixing a quantum dot material with a second organic solvent to form a quantum dot preparation suspension B, wherein the mass percentage of the quantum dot material in the quantum dot preparation suspension B ranges from 1.5% to 40%.

Specifically, the step S102 further includes:

a quantum dot material is provided, the quantum dot material is a hydrophobic material, the quantum dot material comprises a core-shell-ligand structure, and the quantum dot material can form a luminescent layer of a display panel.

Wherein the structure of the hydrophobic ligand comprises a second polar group R ₃ A second nonpolar group R ₄ The second polar group R ₃ Comprising at least one of carboxyl, mercapto, phosphino or amine groups, said second polar group being more capable of coordination than said first polar group R ₁ The coordination ability of the second nonpolar group R ₄ Comprising at least one of an alkyl chain of 6 to 16 carbon atoms, an aromatic group, and an aromatic group substituted with the alkyl chain.

And S103, mixing the dopant preparation solution A, the quantum dot preparation suspension B and a third organic solvent to form the quantum dot ink.

Specifically, the step S103 further includes:

firstly, converting the mass ratio (the mass ratio is between 0.01 and 0.1) of a dopant in a preset quantum dot ink to a quantum dot material to obtain the volume ratio of the dopant preparation solution A to the quantum dot preparation suspension B, and mixing the dopant preparation solution A and the quantum dot preparation suspension B according to the volume ratio and a proper volume of a third part of organic solvent according to a first ratio in a mixing mode to form the quantum dot ink; wherein the mass ratio of the small molecular dopant to the hydrophobic quantum dot material in the quantum dot ink is between 0.01 and 0.1.

Specifically, the first proportion is calculated by converting the mass ratio (the mass ratio is between 0.01 and 0.1) of the dopant and the quantum dot material in the predetermined quantum dot ink to obtain the volume ratio of the solution A and the suspension B.

The preparation method of the quantum dot ink provided by the embodiment of the application is described with reference to specific embodiments.

Example 1

The quantum dot ink provided in the first embodiment comprises 78.5% of mixed organic solvent composed of o-xylene and 20% of phenylcyclohexane, 1.47% of red hydrophobic quantum dot material and 0.03% of dopant by mass percent; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphorus oxide.

Further, the preparation of the quantum dot ink provided in the first embodiment of the present application further includes the following steps:

s101, preparing a mixed organic solvent of dimethylbenzene and phenylcyclohexane according to a preset proportion;

s102, mixing a dopant with a part of the mixed organic solvent to form a dopant preparation solution A with the mass concentration of 1%;

s103, mixing the quantum dot material with another part of mixed organic solvent to form red hydrophobic quantum dot preparation suspension B with the mass concentration of 3%;

S104, converting the mass ratio (the mass ratio is 1:50) of the dopant in the preset quantum dot ink to the red hydrophobic quantum dot material to obtain the volume ratio (the volume ratio is 1:16.33) of the dopant preparation solution A to the red hydrophobic quantum dot preparation suspension B, and mixing 0.03ml of the dopant preparation solution A, 0.49ml of the red hydrophobic quantum dot preparation suspension B and 0.48ml of a third mixed organic solvent in the mixing mode according to the volume ratio to form 1ml of the quantum dot ink; wherein the mixing means is at least one selected from stirring, shaking and ultrasonic dispersion, and the mixing process may be accompanied by a degree of heating. The mixed solution or suspension has the characteristics of clarification and uniformity, and larger agglomerated particles are removed by a polytetrafluoroethylene filter membrane with a pore size of 0.2 microns or 0.45 microns before use.

Example two

The quantum dot ink provided in the second embodiment comprises 78.5% of xylene and 20% of phenylcyclohexane by mass percentage, 1.47% of red hydrophobic quantum dot material and 0.03% of dopant; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphine.

Further, the preparation of the quantum dot ink provided in the fourth embodiment of the present application further includes the following steps:

s101, preparing a mixed organic solvent of o-xylene and phenylcyclohexane according to a preset proportion;

Example III

The quantum dot ink provided in the third embodiment (comprising 67% by mass of a mixed organic solvent composed of phenylcyclohexane and 30% by mass of methyl benzoate, 2.95% by mass of a green hydrophobic quantum dot material and 0.05% by mass of a small molecule dopant, wherein the green hydrophobic quantum dot material is composed of a CdSe core, a ZnSe/ZnS double-layer shell and a 1-dodecyl mercaptan ligand, and the dopant is dodecylprimary amine.

Further, the preparation of the quantum dot ink provided in the second embodiment of the present application further includes the following steps:

s101, preparing a mixed organic solvent of phenylcyclohexane and methyl benzoate according to a predetermined proportion;

s102, mixing a dopant with a part of the mixed organic solvent to form a dopant preparation solution A with the mass concentration of 2%;

s103, mixing the quantum dot material with another part of mixed organic solvent to form a quantum dot preparation suspension B with the mass concentration of 5%;

s104, converting the mass ratio (the mass ratio is 1:59) of the molecular dopant in the predetermined quantum dot ink to the green hydrophobic quantum dot material to obtain the volume ratio (the volume ratio is 1:23.6) of the dopant preparation solution A to the green hydrophobic quantum dot preparation suspension B, and mixing 0.025ml of the dopant preparation solution A, 0.59ml of the green hydrophobic quantum dot preparation suspension B and 0.385ml of a third part of mixed organic solvent in the mixing mode according to the volume ratio to form 1ml of the quantum dot ink; wherein the mixing means is at least one selected from stirring, shaking and ultrasonic dispersion, and the mixing process may be accompanied by a degree of heating. The mixed solution or suspension has the characteristics of clarification and uniformity, and larger agglomerated particles are removed by a polytetrafluoroethylene filter membrane with a pore size of 0.2 microns or 0.45 microns before use.

Example IV

The quantum dot ink provided in the fourth embodiment comprises 67% by mass of a mixed organic solvent composed of phenylcyclohexane and 30% by mass of methyl benzoate, 2.8% by mass of a green hydrophobic quantum dot material and 0.2% by mass of a small molecular dopant; the green hydrophobic quantum dot material is composed of a CdSe core, a ZnSe/ZnS double-layer shell and a 1-dodecyl mercaptan ligand, and the doping agent is dodecyl primary amine.

Further, the preparation of the quantum dot ink provided in the third embodiment of the present application further includes the following steps:

s102, mixing the dopant with a part of the mixed organic solvent to form a dopant preparation solution A with the mass concentration of 2%;

s103, mixing the green quantum dot material with another part of mixed organic solvent to form a green hydrophobic quantum dot preparation suspension B with the mass concentration of 5%;

s104, converting the mass ratio (the mass ratio is 1:59) of the dopant in the preset quantum dot ink to the green hydrophobic quantum dot material to obtain the volume ratio (the volume ratio is 1:23.6) of the dopant preparation solution A to the green hydrophobic quantum dot preparation suspension B, and mixing 0.025ml of the dopant preparation solution A, 0.59ml of the green hydrophobic quantum dot preparation suspension B and 0.385ml of a third part of mixed organic solvent according to the volume ratio in the mixing mode to form 1ml of the quantum dot ink; wherein the mixing means is at least one selected from stirring, shaking and ultrasonic dispersion, and the mixing process may be accompanied by a degree of heating. The mixed solution or suspension has the characteristics of clarification and uniformity, and larger agglomerated particles are removed by a polytetrafluoroethylene filter membrane with a pore size of 0.2 microns or 0.45 microns before use. Comparative example one

The application also provides quantum dot ink compared with the first embodiment and the second embodiment, wherein the quantum dot ink comprises a mixed organic solvent composed of 78.5% of dimethylbenzene and 20% of phenylcyclohexane in percentage by mass and a red hydrophobic quantum dot material with the mass percentage of 1.5%; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand.

Further, the preparation of the quantum dot ink further comprises the following steps:

s102, mixing the quantum dot material with the mixed organic solvent according to a preset mass percent to form 1ml of quantum dot ink; wherein the mixing means is at least one selected from stirring, shaking and ultrasonic dispersion, and the mixing process may be accompanied by a degree of heating. The mixed solution or suspension has the characteristics of clarification and uniformity, and larger agglomerated particles are removed by a polytetrafluoroethylene filter membrane with a pore size of 0.2 microns or 0.45 microns before use.

Comparative example two

The application also provides quantum dot ink compared with the third embodiment and the fourth embodiment, wherein the quantum dot ink comprises a mixed organic solvent composed of 67% by mass of phenylcyclohexane and 30% by mass of methyl benzoate and a green hydrophobic quantum dot material 3% by mass; the green hydrophobic quantum dot material is composed of a CdSe core, a ZnSe/ZnS double-layer shell and a 1-dodecanethiol ligand.

Fig. 2 is a schematic structural diagram of a quantum dot light emitting device according to an embodiment of the present application; wherein the quantum dot light emitting device 10 includes: a substrate 100 and a light emitting functional layer on the substrate 100, wherein the light emitting functional layer comprises a cathode layer 110, an electron functional layer 120 on the cathode layer 110, a quantum dot composite layer on the electron functional layer 120, a hole functional layer on the quantum dot composite layer, and an anode layer 170 on the hole functional layer;

Wherein the quantum dot composite layer is made of the quantum dot ink as described in any one of the above, the quantum dot composite layer comprises a light emitting layer 140, an insulating layer 130 between the electron functional layer 120 and the light emitting layer 140, and the light emitting layer 140 comprises the quantum dot light emitting material described above; the hole-functional layer includes a hole-transporting layer 150 and a hole-injecting layer 160. Wherein the electron functional layer 120 is made of metal oxide, and the first polar group R in the quantum dot ink ₁ A first nonpolar group R in the quantum dot ink coordinated with the metal oxide ₂ The insulating layer 130 is self-assembled on the surface of the metal oxide.

In the embodiment of the present application, the electronic functional layer 120 includes a metal oxide nanocrystal, and the metal oxide nanocrystal includes at least one of zinc oxide, zinc oxide doped with one or more of magnesium, aluminum, and lithium, titanium dioxide, and tin dioxide.

In the embodiment of the present application, the hole transport layer 150 may be selected from an organic material having a hole transport capability, and may be, but is not limited to, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (NPB), N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine (TPD), poly (N, N '-bis (4-butylphenyl) -N, N' -bis (phenyl) benzidine) (poly-TPD), poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (TFB), polyvinylcarbazole (PVK), 4 '-bis (9-Carbazole) Biphenyl (CBP), 4',4 "-tris (carbazole-9-yl) triphenylamine (TCTA), poly (9, 9-dioctylfluorene-CO-bis-N, N-phenyl-1, 4-phenylenediamine) (b), or a mixture thereof.

In the embodiment of the present application, the hole injection layer 160 is made of PEDOT PSS, cuPc, F-TCNQ, HATCN, molybdenum oxide, vanadium oxide, tungsten oxide, chromium oxide, moS ₂ 、WS ₂ 、MoSe ₂ 、WSe ₂ One or more of the following.

In the embodiment of the present application, since the quantum dot light emitting device 10 is an inverted QLED light emitting device, the material of the cathode layer 110 is an anode material of a conventional top light emitting device, and the material of the anode layer 170 is a cathode material of a conventional top light emitting device.

The cathode layer 110 is a high conductive film layer, and the quantum dot light emitting device 10 is a bottom emission type panel, and the conductive film layer is a transparent conductive film layer, and may be made of conductive metal oxides such as ITO (indium tin oxide), IZO (indium zinc oxide), or high conductive organic conductive materials such as graphene, conductive polymers, and the like.

Optionally, in some embodiments of the present application, the anode layer 170 is a reflective electrode (bottom emission type), and the material of the reflective electrode is a highly conductive metal film such as Al or Ag.

In the quantum dot light emitting device 10 provided in the embodiments of the present application, the electronic functional layer 120 is made of metal oxide, and the first polar group R in the quantum dot ink ₁ A first nonpolar group R in the quantum dot ink coordinated with the metal oxide ₂ The insulating layer 130 is self-assembled on the surface of the metal oxide. At the quantum dotDuring the preparation of the optical device 10, the dopant is passed through the first polar group R ₁ The coordination ability with the metal oxide nanocrystals is attached to the surface of the electron functional layer 120 (electron injection layer and electron transport layer), whereby defects at the interface between the electron functional layer 120 and the light emitting layer 140 can be passivated. Within a certain concentration range, the self-assembled single molecule dielectric layer is formed, and the thickness of the single molecule dielectric layer is defined by the density of the single molecule dielectric layer (namely the concentration of the dopant in the quantum dot ink) and the first nonpolar group R of the dopant ₂ Has good uniformity and can be finely controlled to about 1 nm. The accumulation of the nonpolar groups of the dopant renders the single-molecule interlayer insulating, and its extremely thin and controllable thickness has significant advantages for adjusting charge balance in the device and thus improving the efficiency of the quantum dot light emitting device.

In the quantum dot light emitting device 10 provided in the embodiments of the present application, the quantum dot light emitting device 10 can be only an inverted organic light emitting diode device, because of the first nonpolar group R in the quantum dot ink ₂ The insulating layer 130 formed by self-assembly on the surface of the metal oxide is formed between the electron transport layer 120 and the light emitting layer 140 by means of coordination between the polar end group and the metal oxide on the surface of the electron functional layer 120 near the light emitting layer 140. If the quantum dot ink is used for preparing the forward organic light-emitting diode device, the dopant in the quantum dot ink has no self-assembly driving force, and a uniform and orderly insulating layer cannot be formed.

forming an electron function layer 120 on the substrate to which the cathode layer 110 is attached;

forming a quantum dot composite layer on the electron functional layer 120;

forming a hole transport layer 150 on the quantum dot composite layer;

forming a hole injection layer 160 on the hole transport layer 150;

forming an anode layer 170 on the hole injection layer 160;

coating quantum dot ink on the surface of the electronic functional layer, wherein the quantum dot ink comprises a doping agent, a quantum dot material and an organic solvent, the doping agent comprises a first polar group and a first nonpolar group, the first polar group can coordinate with a metal oxide, the first nonpolar group can self-assemble into layers, the first polar group comprises at least one of phosphine groups, amine groups or phosphorus oxide groups, and the first nonpolar group comprises at least one of alkyl chains formed by 6 to 16 carbon atoms, aromatic groups or aromatic groups substituted by the alkyl chains;

Drying the quantum dot ink after being placed for a period of time to form a quantum dot film;

and carrying out thermal annealing treatment on the quantum dot film to form the quantum dot composite layer, wherein the quantum dot composite layer comprises an insulating layer formed on the electronic functional layer and a light-emitting layer formed on the insulating layer.

Specifically, in the embodiment of the present application, the electronic functional layer 120 includes a metal oxide nanocrystal, and the metal oxide nanocrystal includes at least one of zinc oxide, zinc oxide doped with one or more of magnesium, aluminum, and lithium, titanium dioxide, and tin dioxide.

Referring to fig. 2 and fig. 3, fig. 3 is a schematic flow chart of a preparation method of a quantum dot light emitting device according to an embodiment of the present application; specifically, the method comprises the following steps:

s201, an electron functional layer is formed on the cathode layer 110.

Specifically, the step S201 further includes:

first, an electron functional layer 120 is formed on a substrate 100 to which a cathode layer 110 is attached by a solution method, the electron functional layer 120 including an electron injection layer and an electron transport layer; the process of forming the electronic function layer 120 by the solution method may include coating a solution, drying, annealing the dried film, and the like. The coating method of the solution method includes spin coating, blade coating, ink jet printing, and the like. S202, forming a quantum dot composite layer on the electronic functional layer 120, where the quantum dot composite layer includes an insulating layer formed on the electronic functional layer and a light emitting layer formed on the insulating layer.

Specifically, the step S202 further includes:

firstly, the quantum dot ink is coated on the surface of the electronic functional layer 120, wherein the coating mode comprises spin coating, blade coating, ink jet printing, and the like; the quantum dot ink comprises a dopant, a quantum dot material and an organic solvent, wherein the dopant comprises a first polar group and a first nonpolar group, the first polar group can coordinate with a metal oxide, the first nonpolar group can be self-assembled into a layer, the first polar group comprises at least one of a phosphine group, an amine group or a phosphorus oxide group, and the first nonpolar group comprises at least one of an alkyl chain formed by 6 to 16 carbon atoms, an aromatic group or an aromatic group substituted by the alkyl chain.

And secondly, placing the quantum dot ink for a period of time and drying to form a quantum dot film. The method specifically comprises the following steps: placing a wet film formed by the quantum dot ink for 2-10 min under normal pressure, transferring to a vacuum cabin, and drying under reduced pressure to form a quantum dot film; wherein, the quantum dot film can be controlled at 10-35 ℃ in the normal pressure placing process.

And finally, carrying out thermal annealing treatment on the quantum dot film to form a quantum dot composite layer.

Carrying out thermal annealing treatment on the quantum dot film to form a quantum dot composite layer; the thermal annealing temperature of the quantum dot film is between 50 ℃ and 120 ℃ and the time is between 5min and 30 min. Since the quantum dot ink comprises the dopant, the dopant comprises a first polar group R ₁ And a first nonpolar group R ₂ . The first polar group R ₁ Capable of coordinating to metal oxides, said first non-polar group R ₂ Capable of self-assembling into a layer, the first polar group R ₁ Comprising at least one of a phosphine group, an amine group or a phosphorus oxide group, said first nonpolar group comprising at least one R of an alkyl chain consisting of 6 to 16 carbon atoms, an aromatic group or an aromatic group substituted by said alkyl chain ₂ . Wherein the dopant is bound to the first polar group R ₁ The coordination ability with the metal oxide nanocrystals, attached to the surface of the electron functional layer 120 (electron injection/transport layer), forms an insulating layer 130, whereby defects at the surface of the electron functional layer 120 can be passivated. The quantum dot ink further includes the quantum dot material, and finally, a light emitting layer 140 is formed on the insulating layer 130. Further, in the described A hole transport layer 150 is formed on the quantum dot composite layer.

Forming a hole transport layer 150 on the quantum dot composite layer, wherein the deposition mode of the hole transport layer 150 can be respectively selected from a solution method or a vacuum evaporation method; wherein the hole transport layer 150 may be selected from an organic material having hole transport capability, and may be, but is not limited to, N '-diphenyl-N, N' - (1-naphthyl) -1,1 '-biphenyl-4, 4' -diamine (NPB), N '-diphenyl-N, N' -bis (3-methylphenyl) -1,1 '-biphenyl-4, 4' -diamine (TPD), poly (N, N '-bis (4-butylphenyl) -N, N' -bis (phenyl) benzidine) (poly-TPD), poly (9, 9-dioctylfluorene-CO-N- (4-butylphenyl) diphenylamine) (TFB), polyvinylcarbazole (PVK), 4 '-bis (9-Carbazole) Biphenyl (CBP), 4',4 "-tris (carbazole-9-yl) triphenylamine (TCTA), poly (9, 9-dioctylfluorene-CO-bis-N, N-phenyl-1, 4-Phenylenediamine) (PFB), or a mixture thereof.

Still further, a hole injection layer 160 is formed on the hole transport layer 150.

Forming a hole injection layer 160 on the quantum dot composite layer, wherein the deposition mode of the hole injection layer 160 can be respectively selected from a solution method or a vacuum evaporation method; the hole injection layer 160 is made of PEDOT PSS, cuPc, F-TCNQ, HATCN, molybdenum oxide, vanadium oxide, tungsten oxide, chromium oxide, moS ₂ 、WS ₂ 、MoSe ₂ 、WSe ₂ One or more of the following.

Still further, an anode layer 170 is formed on the hole injection layer 160.

Forming an anode layer 170 on the hole injection layer 160, wherein the anode layer 170 may be deposited by a vacuum evaporation method or a sputtering method; the anode layer 170 is a reflective electrode (bottom emission type), and the reflective electrode is made of a highly conductive metal film such as Al or Ag. Specifically, the quantum dot ink provided in the first embodiment of the present application includes a mixed organic solvent composed of 78.5% of xylene and 20% of phenylcyclohexane, 1.47% of red hydrophobic quantum dot material, and 0.03% of dopant; the quantum dot material consists of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphorus oxide.

When the quantum dot INK provided in the first embodiment of the present application is used to prepare the first quantum dot light emitting device (the device number is S-INK 1), the main steps of the preparation include: firstly, a quantum dot wet film is obtained on the surface of a zinc oxide nanocrystal in a spin coating mode, then the quantum dot wet film is placed for 2min at 25 ℃ and normal pressure, then is placed for 10min at 10 ℃/100Pa to be dried, and finally the preparation of the quantum dot composite layer is completed through thermal annealing treatment at 5min and 100 ℃.

Specifically, the quantum dot ink provided in the second embodiment of the present application comprises a mixed organic solvent composed of 78.5% of xylene and 20% of phenylcyclohexane, 1.47% of red hydrophobic quantum dot material and 0.03% of dopant by mass; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphine.

When the quantum dot INK provided in the second embodiment of the present application is used to prepare a second quantum dot light emitting device (device number S-INK 2), the main steps of the preparation include: firstly, a quantum dot wet film is obtained on the surface of a zinc oxide nanocrystal in an ink-jet printing mode, then the quantum dot wet film is placed for 5min at 25 ℃ and normal pressure, then is placed for 15min at 10 ℃/1Pa to be dried, and finally the preparation of a quantum dot composite layer is completed through thermal annealing treatment at 10min and 100 ℃.

Specifically, the quantum dot ink provided in the third embodiment of the present application includes a mixed organic solvent composed of 67% by mass of phenylcyclohexane and 30% by mass of methyl benzoate, 2.95% by mass of a green hydrophobic quantum dot material, and 0.05% by mass of a dopant; the quantum dot material consists of a CdSe core, a ZnSe/ZnS double-layer shell and a dodecyl mercaptan ligand, and the doping agent is dodecyl primary amine.

When the quantum dot INK provided in the third embodiment of the present application is used to prepare a third quantum dot light emitting device (device number S-INK 3), the main steps of the preparation include: firstly, a quantum dot wet film is obtained on the surface of a zinc oxide nanocrystal in an ink-jet printing mode, then the quantum dot wet film is placed for 5min at 25 ℃ and normal pressure, then is placed for 15min at 10 ℃/1Pa to be dried, and finally the preparation of a quantum dot composite layer is completed through thermal annealing treatment at 10min and 100 ℃.

Specifically, the quantum dot ink provided in the fourth embodiment of the present application includes a mixed organic solvent composed of 67% by mass of phenylcyclohexane and 30% by mass of methyl benzoate, 2.8% by mass of a green hydrophobic quantum dot material, and 0.2% by mass of a dopant; the quantum dot material consists of a CdSe core, a ZnSe/ZnS double-layer shell and a dodecyl mercaptan ligand, and the doping agent is dodecyl primary amine.

When the quantum dot INK provided in the fourth embodiment of the present application is used to prepare a fourth quantum dot light emitting device (device number S-INK 4), the main steps of the preparation include: firstly, a quantum dot wet film is obtained on the surface of a zinc oxide nanocrystal in an ink-jet printing mode, then the quantum dot wet film is placed for 5min at 25 ℃ and normal pressure, then is placed for 15min at 10 ℃/1Pa to be dried, and finally the preparation of a quantum dot composite layer is completed through thermal annealing treatment at 10min and 100 ℃.

Specifically, the quantum dot ink provided in the first comparative example of the present application comprises a mixed organic solvent composed of 78.5% by mass of xylene and 20% by mass of phenylcyclohexane, and a red hydrophobic quantum dot material 1.5% by mass; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand.

When the quantum dot ink provided in the first comparative example of the present application is used to prepare a fifth quantum dot light emitting device (device number S-REF 1), the main steps of the preparation thereof include: firstly, a quantum dot wet film is obtained on the surface of zinc oxide nanocrystals in an inkjet printing mode, then the quantum dot wet film is placed for 5min at 25 ℃ and normal pressure, then is placed for 15min at 10 ℃/1Pa to be dried, and finally the preparation of the luminescent layer is completed through thermal annealing treatment at 5min and 100 ℃.

Specifically, the quantum dot ink provided in the second comparative example of the present application comprises a mixed organic solvent composed of 67% by mass of phenylcyclohexane and 30% by mass of methyl benzoate, and a green hydrophobic quantum dot material 3% by mass; the green hydrophobic quantum dot material is composed of a CdSe core, a ZnSe/ZnS double-layer shell and a 1-dodecanethiol ligand.

When a sixth quantum dot light emitting device (device number S-REF 2) was prepared using the quantum dot ink provided in the second comparative example of the present application, the main steps of the preparation thereof included: firstly, a quantum dot wet film is obtained on the surface of zinc oxide nanocrystals in an inkjet printing mode, then the quantum dot wet film is placed for 5min at 25 ℃ and normal pressure, then is placed for 15min at 10 ℃/1Pa to be dried, and finally the preparation of the luminescent layer is completed through thermal annealing treatment at 10min and 100 ℃.

Further, an inverted QLED device is prepared according to the steps shown in fig. 3, the structure of which is shown in fig. 2, wherein the material of the cathode layer 110 is ITO (indium tin oxide), the material of the electronic functional layer 120 is zinc oxide nanocrystals, the quantum dot inks of the above three embodiments of the present application form the insulating layer 130 and the light emitting layer 140 respectively, the quantum dot inks of the above two comparative embodiments of the present application form only the light emitting layer 140, the material of the hole transporting layer 150 is TCTA (4, 4',4″ -tris (carbazole-9-yl) triphenylamine), and the material of the hole injecting layer 160 is MoO ₃ The anode layer 170 is made of silver metal. Quantum dot light emitting devices prepared by using the quantum dot INK of the first embodiment of the present application, the quantum dot INK of the second embodiment of the present application, the quantum dot INK of the third embodiment of the present application, the quantum dot INK of the first comparative embodiment of the present application and the quantum dot INK of the second comparative embodiment of the present application are respectively denoted as "S-INK1 device", "S-INK2 device", "S-INK3 device", "S-INK4 device", "S-REF1 device" and "S-REF2 device".

Specifically, the film layer structures of the six inverted QLED devices described above are shown in the following order from the cathode layer 110 to the anode layer 170:

inverted QLED device S-INK1: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, the electron function layer 120 is zinc oxide nanocrystals, the thickness of the electron function layer 120 is 80-100 nm, preferably 90nm, and the hole transport layer 150 is TCTA (4, 4',4″ -tris (carbazole)-9-yl) triphenylamine), the hole transport layer 150 has a thickness of 50 to 70nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm; the quantum dot ink provided in the first embodiment of the present application forms the insulating layer 130 and the light-emitting layer 140, where the total thickness of the insulating layer 130 and the light-emitting layer 140 is 15-30 nm, preferably 20nm; the quantum dot ink provided in the first embodiment of the present application comprises a mixed organic solvent composed of 78.5% of xylene and 20% of phenylcyclohexane, 1.47% of red hydrophobic quantum dot material and 0.03% of dopant by mass; the quantum dot material consists of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphorus oxide.

Inverted QLED device S-INK2: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, the electron function layer 120 is zinc oxide nanocrystals, the thickness of the electron function layer 120 is 80-100 nm, preferably 90nm, the hole transport layer 150 is TCTA (4, 4' -tris (carbazol-9-yl) triphenylamine), the thickness of the hole transport layer 150 is 50-70 nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm;

the quantum dot ink provided in the second embodiment of the present application forms the insulating layer 130 and the light-emitting layer 140, where the total thickness of the insulating layer 130 and the light-emitting layer 140 is 15-30 nm, preferably 20nm; the quantum dot ink provided in the second embodiment of the present application comprises a mixed organic solvent composed of 78.5% of xylene and 20% of phenylcyclohexane, 1.47% of red hydrophobic quantum dot material and 0.03% of dopant by mass; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand, and the doping agent is tri-n-octyl phosphine. Inverted QLED device S-INK3: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, and the electron function layer 120 is zinc oxide nanocrystals The thickness of the electron functional layer 120 is in the range of 60 to 80nm, preferably 80nm, the hole transport layer 150 is TCTA (4, 4' -tris (carbazol-9-yl) triphenylamine), the thickness of the hole transport layer 150 is 40 to 60nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm; the quantum dot ink provided in the third embodiment of the present application forms the insulating layer 130 and the light-emitting layer 140, where the total thickness of the insulating layer 130 and the light-emitting layer 140 is 15-25 nm, preferably 20nm; the quantum dot ink provided in the third embodiment of the present application comprises 67% by mass of a mixed organic solvent composed of phenylcyclohexane and 30% by mass of methyl benzoate, 2.95% by mass of a green hydrophobic quantum dot material, and 0.05% by mass of a dopant; the quantum dot material consists of a CdSe core, a ZnSe/ZnS double-layer shell and a dodecyl mercaptan ligand, and the doping agent is dodecyl primary amine.

Inverted QLED device S-INK4: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, the electron function layer 120 is zinc oxide nanocrystals, the thickness of the electron function layer 120 is in the range of 60-80 nm, preferably 80nm, the hole transport layer 150 is TCTA (4, 4' -tris (carbazol-9-yl) triphenylamine), the thickness of the hole transport layer 150 is 40-60 nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm;

the quantum dot ink provided in the fourth embodiment of the present application forms the insulating layer 130 and the light-emitting layer 140, where the total thickness of the insulating layer 130 and the light-emitting layer 140 is 15-25 nm, preferably 20nm; the quantum dot ink provided in the fourth embodiment of the present application comprises 67% by mass of a mixed organic solvent composed of phenylcyclohexane and 30% by mass of methyl benzoate, 2.8% by mass of a green hydrophobic quantum dot material, and 0.2% by mass of a dopant; wherein the quantum dot material consists of a CdSe core, a ZnSe/ZnS double-layer shell and a dodecanethiol ligand, and the doping agent is twelvePrimary alkyl amines. Inverted QLED device S-REF1: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, the electron function layer 120 is zinc oxide nanocrystals, the thickness of the electron function layer 120 is 80-100 nm, preferably 90nm, the hole transport layer 150 is TCTA (4, 4' -tris (carbazol-9-yl) triphenylamine), the thickness of the hole transport layer 150 is 50-70 nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm;

wherein the quantum dot ink provided in the first comparative example of the present application forms the light emitting layer 140, and the thickness of the light emitting layer 140 is 15-30 nm, preferably 20nm; the quantum dot ink provided in the first comparative example of the present application comprises a mixed organic solvent composed of 78.5% by mass of xylene and 20% by mass of phenylcyclohexane, and a red hydrophobic quantum dot material 1.5% by mass; the red hydrophobic quantum dot material is composed of an InP core, a ZnS shell and an oleylamine ligand.

Inverted QLED device S-REF2: the cathode layer 110 is ITO, the thickness of the cathode layer 110 is 50nm, the electron function layer 120 is zinc oxide nanocrystals, the thickness of the electron function layer 120 is in the range of 60-80 nm, preferably 80nm, the hole transport layer 150 is TCTA (4, 4' -tris (carbazol-9-yl) triphenylamine), the thickness of the hole transport layer 150 is 40-60 nm, preferably 60nm, and the hole injection layer 160 is MoO ₃ The thickness of the hole injection layer 160 is 5-10 nm, preferably 8nm, the anode layer 170 is silver metal, and the thickness of the anode layer 170 is 100nm;

Wherein the quantum dot ink provided in the second comparative example of the present application forms the light emitting layer 140, and the total thickness of the light emitting layer 140 is 15 to 25nm, preferably 20nm; the quantum dot ink provided in the second comparative example of the present application comprises 67% by mass of a mixed organic solvent composed of phenylcyclohexane and 30% by mass of methyl benzoate, and 3% by mass of a green hydrophobic quantum dot material; the green hydrophobic quantum dot material is composed of a CdSe core, a ZnSe/ZnS double-layer shell and a 1-dodecanethiol ligand.

Finally, the maximum external quantum efficiency of the six quantum dot light emitting devices is tested respectively, and the device performance results are shown in table 1:

device numbering	Maximum external quantum efficiency (%)
		S-INK1	3.6％
S-INK2	3.5％
		S-INK3	11.2％
S-INK4	9.7％
		S-REF1	2.2％
S-REF2	8.5％

TABLE 1

As can be seen from table 1 above, when the inverted QLED device S-INK1 and the inverted QLED device S-INK2 are compared with the inverted QLED device S-REF1 of the first comparative example of the present application, the addition of a small molecular dopant with a certain concentration to the quantum dot INK can increase the maximum external quantum efficiency of the quantum dot light emitting diode device; compared with the inverted QLED device S-INK3 and the inverted QLED device S-INK4 in the second comparative example, when the same quantum dot material is adopted, the maximum external quantum efficiency of the quantum dot light emitting diode device can be improved by adding a small molecular dopant with a certain concentration into the quantum dot INK, and the maximum external quantum efficiency of the quantum dot light emitting diode device is reduced due to the fact that the concentration of the small molecular dopant is too high.

Wherein, the inverted QLED device S-INK1, the inverted QLED device S-INK2 and the inverted QLED device S-REF1 are all red hydrophobic quantum dot materials composed of InP cores, znS shells and oleylamine ligands, and the inverted QLED device S-INK3, the inverted QLED device S-INK4 and the inverted QLED device S-REF2 are all green hydrophobic quantum dot materials composed of CdSe cores, znSe/ZnS double-layer shells and dodecanethiol ligands.

Further, due to the relatively large performance difference between the two quantum dot materials, the different quantum dot materials have a great influence on the maximum external quantum efficiency of the inverted QLED device. Therefore, the maximum external quantum efficiency of an inverted quantum dot light emitting device when different quantum dot materials are used may also be greatly different.

When the quantum dot ink provided by the embodiment of the application is used for preparing the inverted quantum dot luminescent device, the self-assembly effect of the small molecular dopant on the surface of the electron injection/transmission layer is utilized to form the insulating layer with uniform and controllable thickness and extremely thin thickness. The insulating layer has the following two beneficial effects: (1) Inhibiting exciton quenching at the interface between the electron injection/transport layer and the light-emitting layer, and improving quantum yield of exciton radiative transition; (2) The injection of electrons into the light emitting layer is reduced, promoting charge balance in the device. Therefore, the efficiency of the QLED device can be improved on the premise of not introducing an additional functional layer deposition step.

Correspondingly, the embodiment of the application also provides a display device which comprises the quantum dot light emitting diode or the quantum dot light emitting diode prepared by the preparation method of the quantum dot light emitting diode.

According to the quantum dot ink, the quantum dot light emitting diode, the preparation method thereof and the display device, when the quantum dot ink is deposited on the surface of the electronic functional layer formed by the metal oxide nanocrystals, the polar groups of the small molecular dopants can coordinate with the metal oxide and are attached to the surface of the electronic functional layer; meanwhile, hydrophobic nonpolar groups produce the effect of self-assembled insulating layers on the surface of the electronic functional layer. Therefore, the effects of passivating the surface defects of the metal oxide nanocrystals, inhibiting exciton quenching at the interface and weakening electron injection can be achieved, and the luminous efficiency of the quantum dot display panel is further improved.

In summary, according to the quantum dot ink, the quantum dot light emitting diode, the preparation method thereof and the display device provided by the embodiments of the present application, the dopant containing the first polar group and the first nonpolar group is added into the quantum dot ink, the first polar group can coordinate with the metal oxide, the first nonpolar group can self-assemble into layers, the first polar group comprises at least one of phosphine group, amine group or phosphorus oxide group, the first nonpolar group comprises at least one of alkyl chain, aromatic group or aromatic group substituted by the alkyl chain formed by 6 to 16 carbon atoms, wherein the first polar group has a metal oxide coordination ability similar to or weaker than that of the hydrophobic ligand of the quantum dot material in the quantum dot ink, and the concentration of the dopant in the quantum dot ink is lower, so that the dopant does not undergo ligand exchange reaction with the hydrophobic ligand in the quantum dot ink, but mainly exists in a dissolved and dispersed molecular form; when the equivalent quantum dot ink is deposited on the surface of the electronic functional layer, the first polar group can generate coordination action with the surface of one side, far away from the substrate, of the electronic functional layer and is attached to the electronic functional layer, meanwhile, the hydrophobic chain segment of the first nonpolar group forms a self-assembled insulating layer on the electronic functional layer, the insulating layer can passivate the surface defect of the electronic functional layer, further exciton quenching at the interface between the light-emitting layer and the electronic functional layer is inhibited, the effect of electron injection is further weakened, and the light-emitting efficiency of the quantum dot light-emitting diode is further improved.

In the foregoing embodiments, the descriptions of the embodiments are emphasized, and for parts of one embodiment that are not described in detail, reference may be made to related descriptions of other embodiments.

The quantum dot ink, the preparation method thereof and the display panel provided by the embodiment of the application are described in detail, and specific examples are applied to illustrate the principle and the implementation of the application, and the description of the above examples is only used for helping to understand the method and the core idea of the application; meanwhile, those skilled in the art will have variations in the specific embodiments and application scope in light of the ideas of the present application, and the present description should not be construed as limiting the present application in view of the above.

Claims

1. The quantum dot ink is characterized by comprising a doping agent, a quantum dot material and an organic solvent;

wherein the dopant comprises a first polar group capable of coordinating with the metal oxide, the first nonpolar group capable of self-assembling into a layer, the first polar group comprising at least one of a phosphine group, an amine group, or a phosphorus oxy group, and a first nonpolar group comprising at least one of an alkyl chain composed of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with the alkyl chain;

The quantum dot material comprises a hydrophobic ligand, wherein the coordination ability of the hydrophobic ligand and a metal oxide is not weaker than the coordination ability of the first polar group in the dopant and the metal oxide; the hydrophobic ligand includes a second polar group including at least one of a carboxyl group, a mercapto group, a phosphine group, or an amine group, and a second nonpolar group including at least one of an alkyl chain composed of 6 to 16 carbon atoms, an aromatic group, or an aromatic group substituted with the alkyl chain;

the organic solvent includes chain alkanes, cycloalkanes, haloalkanes, aromatic hydrocarbons, derivatives of chain alkanes, cycloalkanes, haloalkanes, aromatic hydrocarbons, and combinations thereof;

the mass ratio of the doping agent to the quantum dot material is 1% -10%.

2. The quantum dot ink of claim 1, wherein the dopant has a molecular weight of less than 500.

3. The quantum dot ink of claim 1, wherein the organic solvent has a melting point of less than or equal to 0 ℃ and a boiling point range of 100 ℃ to 300 ℃.

4. The quantum dot ink according to claim 1, wherein the mass percentage of the organic solvent in the quantum dot ink is 79.8% -98.97%, the mass percentage of the quantum dot material in the quantum dot ink is 1% -20%, and the mass percentage of the dopant in the quantum dot ink is 0.03% -0.2%.

5. The quantum dot ink of claim 1, wherein the dopant comprises any one of diphenyl phosphine, diphenyl phosphine chloride, tri-n-octyl phosphine, n-hexylamine, 4-hexylaniline, 4-hexylchloroaniline, tri-n-octyl phosphorus oxide, diphenyl phosphorus oxide, dodecyl primary amine.

6. A quantum dot light emitting diode comprising a light emitting layer made of the quantum dot ink of any one of claims 1 to 5 and an electron functional layer made of a metal oxide;

7. The quantum dot light emitting diode of claim 6, wherein the metal oxide comprises at least one of zinc oxide, titanium dioxide, or tin dioxide.

8. The preparation method of the quantum dot light emitting diode is characterized by comprising the following steps of:

forming an electron function layer on the cathode layer;

coating the quantum dot ink according to any one of claims 1 to 5 on the surface of the electronic functional layer; drying the quantum dot ink to form a quantum dot film;

9. A display device comprising the quantum dot light-emitting diode according to claim 6 or 7 or the quantum dot light-emitting diode prepared by the method for preparing the quantum dot light-emitting diode according to claim 8.