WO2022153443A1

WO2022153443A1 - Method for manufacturing quantum dot dispersion, quantum dot dispersion, and light-emitting device

Info

Publication number: WO2022153443A1
Application number: PCT/JP2021/001067
Authority: WO
Inventors: 裕真矢口
Original assignee: シャープ株式会社
Priority date: 2021-01-14
Filing date: 2021-01-14
Publication date: 2022-07-21

Abstract

This method for manufacturing a quantum dot dispersion includes a stirring step and a retrieval step. In the stirring step, a first liquid (38) and a second liquid (40) are stirred. The first liquid includes quantum dots (16) and a non-polar solvent (42). The second liquid includes ligands (22) that can be coordinated to the quantum dots and that include cations or anions, an ion liquid (30), and a non-aqueous polar solvent (20). In the retrieval step, a fourth liquid (52) is retrieved, the fourth liquid including quantum dots from a third liquid (50) obtained in the stirring step, a coordination compound that includes the ligands and the ion liquid, and the non-aqueous polar solvent. The non-aqueous polar solvent includes at least one from among lower alcohols, lower glycols, lower glycol esters, and lower glycol ethers.

Description

Quantum dot dispersion system manufacturing method, quantum dot dispersion system, light emitting device

The present invention relates to a quantum dot dispersion system and a method for manufacturing the same.

Patent Document 1 discloses a technique for covalently bonding a surface-modified portion of phosphor particles and a polymer derived from an ionic liquid in order to improve the dispersibility of the phosphor particles.

Japanese Patent Application Laid-Open No. 2018-137281

In the method disclosed in Patent Document 1, since it is necessary to expose the phosphor particles to water, the surface of the fluorescent particles may be deteriorated.

In order to solve the above problems, the method for producing a quantum dot dispersion system according to the uniformity of the present invention comprises (1) a first liquid containing a quantum dot and a non-polar solvent, and (2) the quantum dots. From a stirring step of stirring a ligand containing a cation or an anion, an ionic liquid, and a second liquid containing a non-aqueous polar solvent, and a third liquid obtained by the stirring step. The non-aqueous polar solvent comprises a coordinator containing the quantum dots, the ligand and the ionic liquid, and a take-out step of taking out a fourth liquid containing the non-aqueous polar solvent. It contains at least one of an alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether.

Further, the quantum dot dispersion system according to the uniformity of the present invention is at least one of a quantum dot, a coordinator capable of coordinating the quantum dot, and a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether. It is provided with a non-aqueous polar solvent containing, and the content of water is 0% by volume or more and 0.1% by volume or less with respect to the total volume.

Further, the light emitting device according to the uniform state of the present invention includes at least one of a light emitting layer and a wavelength conversion layer for converting the wavelength of light emitted from the light source as an optical layer, and the above one or more. The first optical layer among the optical layers is a non-optical layer containing at least one of a quantum dot, a coordinator capable of coordinating the quantum dot, and a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether. It is provided with an aqueous polar solvent, and the content of water is 0% by volume or more and 0.1% by volume or less with respect to the total volume of the first optical layer.

It is possible to manufacture a dispersion system containing the quantum dots coordinated by the coordinator and a light emitting device formed from the dispersion system without the contact of water with the quantum dots, and it is possible to reduce the deterioration of the quantum dots.

It is a process sectional view which shows the method of manufacturing the quantum dot dispersion system which concerns on Embodiment 1. FIG. It is the schematic sectional drawing which shows the light emitting device which concerns on Embodiment 1. FIG. It is a schematic enlarged view which shows the quantum dot which concerns on Embodiment 1. FIG. It is a schematic enlarged view which shows the vicinity of the outer surface of the quantum dot which concerns on Embodiment 1. FIG. It is the schematic which shows the example of the coordination structure which concerns on Embodiment 1. FIG. It is a flowchart which shows the method of manufacturing the light emitting layer which concerns on Embodiment 1. It is a schematic diagram for demonstrating the mechanism of recoordination to a quantum dot of the coordination structure which concerns on Embodiment 1. FIG. It is a schematic enlarged view which shows the vicinity of the outer surface of the quantum dot which concerns on Embodiment 2. It is the schematic which shows the example of the coordination structure which concerns on Embodiment 2. It is a flowchart which shows the method of manufacturing the light emitting layer which concerns on Embodiment 3. It is a process sectional view which shows the method of manufacturing the quantum dot dispersion system which concerns on Embodiment 3. FIG. It is another process sectional view which shows the method of manufacturing the quantum dot dispersion system which concerns on Embodiment 3. FIG. It is a schematic enlarged view which shows the vicinity of the outer surface of the quantum dot which concerns on Embodiment 4. FIG. It is a flowchart which shows the method of manufacturing the light emitting layer which concerns on Embodiment 4. It is the schematic sectional drawing which shows the light emitting device which concerns on Embodiment 5.

[Embodiment 1]
<Overview of light emitting device>
FIG. 2 is a schematic cross-sectional view of the light emitting device 1 according to the present embodiment. As shown in FIG. 2, the light emitting device 1 according to the present embodiment includes a light emitting element 2 and an array substrate 3. The light emitting device 1 has a structure in which each layer of the light emitting element 2 is laminated on an array substrate 3 on which a TFT (Thin Film Transistor) (not shown) is formed. In this specification, the direction from the light emitting element 2 of the light emitting device 1 to the array substrate 3 is described as "downward", and the direction opposite to the downward direction is described as "upward".

The light emitting element 2 includes a hole transport layer 6, a light emitting layer 8 as an optical layer, an electron transport layer 10, and a cathode 12 on the anode 4 in this order from the lower layer. The anode 4 of the light emitting element 2 formed on the upper layer of the array substrate 3 is electrically connected to the TFT of the array substrate 3.

The light emitting element according to another embodiment may have a cathode on the upper layer of the array substrate. In this case, the light emitting device may include an electron transport layer, a light emitting layer as an optical layer, a hole transport layer, and an anode on the cathode in this order.

<Outline of light emitting element>
Hereinafter, the configuration of each layer of the light emitting element 2 will be described in more detail.

The anode 4 and the cathode 12 contain a conductive material and are electrically connected to the hole transport layer 6 and the electron transport layer 10, respectively.

Either one of the anode 4 and the cathode 12 is a transparent electrode. As the transparent electrode, for example, ITO, IZO, ZnO, AZO, BZO, FTO or the like is used, and a film may be formed by a sputtering method or the like. Further, either the anode 4 or the cathode 12 may contain a metal material, and as the metal material, Al, Cu, Au, Ag or Mg having high reflectance of visible light or an alloy thereof is preferable. ..

The hole transport layer 6 is a layer that transports holes from the anode 4 to the light emitting layer 8. As the material of the hole transport layer 6, an organic or inorganic material conventionally used in a light emitting device containing quantum dots, an organic EL light emitting device, or the like can be used. As the organic material of the hole transport layer 6, a conductive compound such as CBP, PPV, PEDOT-PSS, TFB, or PVK can be used. As the inorganic material of the hole transport layer 6, a metal oxide such as molybdenum oxide, NiO, Cr _2O ₃ , MgO, MgZnO, LaNiO ₃ , or WO ₃ can be used. In particular, as the material of the hole transport layer 6, a material having a large electron affinity and an ionization potential is suitable.

The electron transport layer 10 is a layer that transports electrons from the cathode 12 to the light emitting layer 8. As the material of the electron transport layer 10, in addition to TiO ₂ , an organic or inorganic material conventionally used in a light emitting device containing quantum dots, an organic EL light emitting device, or the like can be used. As the organic material of the electron transport layer 10, a conductive compound such as Alq3, BCP or t-Bu-PBD can be used. As the inorganic material of the electron transport layer 10, a metal oxide such as ZnO, ZAO, ITO, IGZO or electride can be used. In particular, as the material of the electron transport layer 10, a material having a small electron affinity is suitable.

In the present embodiment, the hole transport layer 6 and the electron transport layer 10 can be formed by a vacuum vapor deposition method, a sputtering method, a coating forming method using a colloidal solution, or the like using the above-mentioned materials. Further, the light emitting device 2 may include a hole injection layer between the anode 4 and the hole transport layer 6, and may include an electron injection layer between the cathode 12 and the electron transport layer 10. May be good. Further, the light emitting element 2 may include an intermediate layer between the hole transport layer 6 and the light emitting layer 8, or between the electron transport layer 10 and the light emitting layer 8. The hole injection layer, the electron injection layer, and the intermediate layer may all be formed by the same method as the hole transport layer 6 or the electron transport layer 10.

<Light emitting layer and quantum dots>
The light emitting layer 8 is a layer containing a plurality of quantum dot structures 14 including quantum dots (semiconductor nanoparticles). The quantum dot structure 14 included in the light emitting layer 8 according to the present embodiment will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view of the quantum dot structure 14, and is an enlarged view showing the region A of FIG. In the present embodiment, as shown in FIG. 3, the quantum dot structure 14 includes the quantum dots 16, the surface modification portion 18, and the non-aqueous polar solvent 20.

The quantum dot 16 may be, for example, a quantum dot having a core / shell structure including a core and a shell formed around the core. In this case, the recombination of electrons and holes injected into the quantum dots 16 occurs mainly in the core. In addition, the shell has a function of suppressing the occurrence of core defects or dangling bonds, and reducing the recombination of carriers through the deactivation process. The material of the quantum dot 16 may include a core material of the quantum dot having a conventionally known core / shell and a material used for the shell material.

For example, in the present embodiment, the quantum dot 16 may be, for example, a semi-Cd-based conductor nanoparticle having CdSe in the core and ZnS in the shell. Alternatively, the quantum dots 16 may be, for example, semi-Cd-based conductor nanoparticles having CdSe in the core and ZnSe in the shell.

In addition, the quantum dot 16 may have CdSe / CdS, InP / ZnS, ZnSe / ZnS, CIGS / ZnS, or the like as a core / shell structure. The shell of the quantum dots 16 may be formed of a plurality of layers including a plurality of materials different from each other.

The core of the quantum dot 16 is a luminescent material that has a valence band level and a conduction band level, and emits light by recombination of holes in the valence band level and electrons in the conduction band level. Since the light emitted from the quantum dots 16 has a narrow spectrum due to the quantum confinement effect, it is possible to obtain light emission with a relatively deep chromaticity.

The particle size of the quantum dots 16 is about 1 to 100 nm. The wavelength of light emitted from the quantum dots 16 can be controlled by the particle size. In particular, when the quantum dots 16 have a core / shell structure, the wavelength of light emitted from the quantum dots 16 can be controlled by controlling the particle size of the core. Therefore, by controlling the particle size of the core of the quantum dot 16, the wavelength of the light emitted by the light emitting device 1 can be controlled.

Here, the quantum dot structure 14 in the light emitting layer 8 does not need to be regularly arranged as shown in FIG. 2, and the quantum dot structure 14 may be randomly included in the light emitting layer 8. The film thickness of the light emitting layer 8 may be about 1 nm to 100 nm.

The light emitting device 1 according to the present embodiment includes, but is not limited to, one light emitting element 2 including a light emitting layer 8 provided with one type of quantum dots 16. For example, the light emitting device 1 may include a plurality of types of quantum dots 16 having different light emitting colors from each other in the light emitting layer 8. In this case, the light emitting device 1 may have a plurality of light emitting elements 2 each having quantum dots 16 having different light emitting colors.

Further, the light emitting device 1 may have a plurality of pixels having a plurality of sub pixels, and may be provided with the above-mentioned light emitting element 2 one by one for each of the sub pixels. In this case, the light emitting elements 2 included in the sub-pixels included in the same pixel may have different light emitting colors. Further, the light emitting device 1 may individually drive the light emitting element 2 provided in each sub-pixel. In this case, the light emitting device 1 can configure a display device having a plurality of pixels.

A plurality of surface modification portions 18 are formed on the outermost surface 16S of each quantum dot 16 to modify the quantum dots 16. For example, when the quantum dot 16 has the core / shell structure described above, the surface modification unit 18 may modify the outer surface of the shell of the quantum dot 16. The detailed structure of the surface modification portion 18 will be described later. Although the surface modification portion 18 is shown as a straight line in FIG. 3, the surface modification portion 18 does not necessarily have a linear structure and may have a bent structure.

The surface modification portion 18 has a function of suppressing the occurrence of defects in the quantum dots 16 or dangling bonds. In addition, the surface modification portion 18 reduces the aggregation of the quantum dots 16, protects the quantum dots 16 from the surrounding environment, imparts electrical stability to the surface of the quantum dots 16, or dissolves the quantum dots 16 in a solvent. It has the effect of improving sex or dispersibility.

The non-aqueous polar solvent 20 is held in the vicinity of the outermost surface 16S of the quantum dots 16. In particular, the non-aqueous polar solvent 20 is held on the outermost surface 16S side of the quantum dots 16 between the plurality of non-volatile surface modification portions 18 located around the quantum dots 16. Specific examples of the non-aqueous polar solvent 20 will be described later.

<Ligand>
The specific structure of the surface modification portion 18 will be described with reference to FIG. 4, including the arrangement relationship between the outermost surface 16S of the quantum dots 16 and the non-aqueous polar solvent 20. FIG. 4 is a schematic enlarged view showing the vicinity of the outermost surface 16S of the quantum dot 16, and is an enlarged view showing the region B of FIG.

The surface modification portion 18 contains at least a ligand 22. The ligand 22 contains a coordination functional group 24, a carbon chain 26, and a cation portion 28. The coordination functional group 24 is a functional group that can be coordinated to the outermost surface 16S of the quantum dot 16. In other words, the coordination functional group 24 contains a functional group capable of forming a coordination bond with the outermost surface 16S of the quantum dot 16. Therefore, in the present embodiment, the surface modification portion 18 is formed by the coordination of the ligand 22 to the quantum dot 16 via the coordination bond between the coordination functional group 24 and the outermost surface 16S of the quantum dot 16. Modifies the quantum dot 16. The carbon chain 26 is formed between the coordination functional group 24 and the cation portion 28, and bonds with both the coordination functional group 24 and the cation portion 28. The cation portion 28 is a moiety containing a cation formed at the end of the carbon chain 26 opposite to the coordination functional group 24.

In the present embodiment, the surface modification portion 18 further includes an ionic liquid 30. The ionic liquid 30 is a salt that exhibits liquid properties at room temperature and contains an anion portion 32 containing an anion and a cation portion 34 containing a cation. The ionic liquid 30 binds to the ligand 22 by forming an ionic bond with the cation portion 28 of the ligand 22 by the anion portion 32. Therefore, the surface modification portion 18 includes the ligand 22 and the ionic liquid 30, and becomes a coordinator capable of coordinating with the quantum dots 16.

A specific example of the surface modification portion 18 according to the present embodiment will be described with reference to FIG. In this embodiment, the ligand 22 may be, for example, 2-diethylaminoethanethiol hydrochloride represented by the following chemical formula.

In this case, as shown in FIG. 5, the ligand 22 contains a sulfur atom in the coordination functional group 24 and a quaternary ammonium ion in the cation portion 28.

Further, in the present embodiment, the ionic liquid 30 may be 2- (methacryloyloxy) -ethyltrimethylammonium bis (trifluoromethanesulfonyl) imide. In this case, the anion portion 32 of the ionic liquid 30 becomes, for example, a bis (trifluoromethanesulfonyl) imide shown in the following chemical formula, and the anion 32A of the anion portion 32 shown in FIG. 5 and the cation portion 28 of the ligand 22 Form an ionic bond.

Further, the cation portion 34 of the ionic liquid 30 is, for example, 2- (methacryloyloxy) -ethyltrimethylammonium represented by the following chemical formula.

To further generalize the structure of the surface modification portion 18, for example, the ligand 22 may have a structure represented by the following chemical formula (1).

In the chemical formula (1), A represents the coordination functional group 24 and is selected from a thiol group, a carboxyl group, a phosphono group, or an amino group. R1, R2, and R3 are each selected from an H atom, a methyl group, an ethyl group, a propyl group, or an isopropyl group. n1 is a natural number representing the number of carbon atoms in the carbon chain 26 of the ligand 22, and is 1 or more and 3 or less. The range of n1 corresponds to the range in which the ligand 22 is soluble in a polar solvent.

The anion portion 32 of the ionic liquid 30 contains bis (trifluoromethanesulfonyl) imide, thiosalicylic acid, tetrafluoroborate, hexafluorophosphate, dibutyl phosphate, acetic acid, disyanamide, nitrate, hydrogen sulfate, octyl sulfate, and methanesulfon. Includes at least one from the group consisting of acids, thiosocyanic acids, trifluoromethanesulfonic acids, aminoacetic acids, and ethylsulfates.

Further, the cation portion 34 of the ionic liquid 30 contains at least one species from the group consisting of aliphatic quaternary ammonium ions, imidazolium ions, pyridinium ions, phosphonium ions, pyrrolidinium ions, piperidinium ions, and sulfonium ions.

As shown in FIG. 4, the non-aqueous polar solvent 20 is held in the vicinity of the outermost surface 16S of the quantum dots 16 and between a plurality of surface modification portions 18 that modify the quantum dots 16. In particular, in the present embodiment, the entire ligand 22 coordinated to the quantum dot 16 is located in the non-aqueous polar solvent 20 held in the vicinity of the outermost surface 16S of the quantum dot 16.

<Manufacturing method of light emitting device>
Hereinafter, a method for manufacturing the light emitting device 1 will be described. The light emitting device 1 may be manufactured by forming an array substrate 3 and forming each layer of a light emitting element 2 on the array substrate 3 in order from the anode 4. Of the layers of the light emitting element 2, the layers other than the light emitting layer 8 may be formed by the method described with reference to FIG.

The method of forming the light emitting layer 8 according to the present embodiment will be described with reference to FIG. In this embodiment, as will be described in detail later, the light emitting layer 8 is formed by applying the dispersion system of the quantum dots 16 obtained by stirring the first liquid and the second liquid onto the hole transport layer 6. To form. Regarding the method for forming the light emitting layer 8 according to the present embodiment, the first liquid and the second liquid will be described with reference to FIG. 1, which is a process cross-sectional view for explaining the stirring step of stirring the first liquid and the second liquid. It will be explained together with.

<Stirring of 1st and 2nd liquids>
In the method for forming the light emitting layer 8 according to the present embodiment, first, the generation of the first liquid (step S2) and the generation of the second liquid (step S4) are executed. Next, the first liquid and the second liquid are stirred in the container 36 shown in FIG. 1 (step S6), and the stirring step is executed. Here, in step S6A of FIG. 1, the state immediately before starting the stirring of the first liquid 38 and the second liquid 40 injected into the container 36 in step S6 is shown.

As shown in step S6A of FIG. 1, the first liquid 38 is a solution in which a plurality of quantum dots 16 in which a plurality of ligands 44 are coordinated are dispersed in a non-polar solvent 42. The non-polar solvent 42 is not particularly limited as long as it is a non-polar solvent in which the quantum dots 16 are soluble, and may be, for example, a non-polar organic solvent containing octane. The ligand 44 is not particularly limited as long as it has a coordination functional group 46 for coordinating to the quantum dot 16 and is soluble in the non-polar solvent 42. Specifically, the ligand 44 may be dodecanethiol, oleic acid, oleylamine, or the like. The first liquid 38 may be produced by dispersing the quantum dots 16 and the ligand 44 in a non-polar solvent 42 and stirring them appropriately.

For simplicity of illustration, the first liquid 38 shown in FIG. 1 shows only a part of the ligand 44 coordinated to the quantum dot 16. Along with this, the ligand 44 is shown so as to be biasedly coordinated to a part of the outer peripheral surface of the quantum dot 16, but the ligand 44 is not limited to this, and the ligand 44 is formed on the outer peripheral surface of the quantum dot 16. Coordination may be performed substantially uniformly over the entire surface.

As shown in step S6A of FIG. 1, the second liquid 40 is a solution in which the ligand 22 and the ionic liquid 30 are dispersed in the non-aqueous polar solvent 20. The second liquid 40 may further contain counter ion 48, which is an anion that ionically bonds with the cation of the cation portion 28 of the ligand 22, in the non-aqueous polar solvent 20. The second liquid 40 may be produced by mixing a solution in which the ligand 22 is dispersed in the non-aqueous polar solvent 20 and a solution in which the ionic liquid 30 is dispersed in the non-aqueous polar solvent 20.

Since the non-polar solvent 42 and the non-aqueous polar solvent 20 have different polarities from each other, the first liquid 38 and the second liquid 40 are separated in the container 36. Further, for example, when the specific gravity of the second liquid 40 is lighter than the specific gravity of the first liquid 38, the second liquid 40 is located at the upper part in the container 36 than the first liquid 38.

When the first liquid 38 and the second liquid 40 are stirred, the cation of the cation portion 28 of the ligand 22 and the anion of the anion portion 32 of the ionic liquid 30 are ionic bonded to form a surface modification portion. 18 is formed. Further, by stirring the first liquid 38 and the second liquid 40, the ligand coordinated to the quantum dot 16 becomes an equilibrium state between the ligand 22 and the ligand 44.

Here, when the surface modification portion 18 is formed by the ligand 22 and the ionic liquid 30 in the first liquid 38, the concentration of the surface modification portion 18 becomes excessive as compared with the concentration of the quantum dots 16. As such, the first liquid 38 contains an excess amount of the ligand 22 and the ionic liquid 30. Therefore, when the first liquid 38 and the second liquid 40 are sufficiently stirred, the ligand coordinated to the quantum dot 16 is replaced from the ligand 44 to the ligand 22.

<Production of 3rd liquid and removal of 4th liquid>
Step S6B of FIG. 1 shows the state in the container 36 after the first liquid 38 and the second liquid 40 are sufficiently stirred and then allowed to stand for a sufficient time. When the first liquid 38 and the second liquid 40 are sufficiently stirred, the third liquid 50 shown in step S6B of FIG. 1 is generated. The third liquid 50 includes the fourth liquid 52 and the fifth liquid 54.

As shown in step S6B of FIG. 1, the fourth liquid 52 is a solution in which the quantum dots 16 modified by the surface modification portion 18 are dispersed in the non-aqueous polar solvent 20. Since the ligand 22 and the ionic liquid 30 both have ions, they have relatively strong polarities. Therefore, the surface modification portion 18 containing the ligand 22 and the ionic liquid 30 is more soluble in the non-aqueous polar solvent 20 than in the non-polar solvent 42.

Therefore, the quantum dots 16 modified by the surface modification portion 18 are more soluble in the non-aqueous polar solvent 20 than in the non-polar solvent 42, as compared with the quantum dots 16 to which the ligand 44 is coordinated. Therefore, when the first liquid 38 and the second liquid 40 are sufficiently stirred, the quantum dot 16 is a ligand in which the coordinating ligand is bound from the ligand 44 to the ionic liquid 30. With the replacement with 22, the non-polar solvent 42 moves to the non-aqueous polar solvent 20. Therefore, the fourth liquid 52 is a solution in which the quantum dots 16 modified by the surface modification portion 18 are dispersed in the non-aqueous polar solvent 20.

Similar to the ligand 44 in the first liquid 38 shown in FIG. 1, in the fourth liquid 52 shown in FIG. 1, only a part of the surface modification portion 18 that modifies the quantum dots 16 is shown. Along with this, the surface modification portion 18 is shown so as to be biased to a part of the outer peripheral surface of the quantum dot 16, but the surface modification portion 18 is not limited to this, and the surface modification portion 18 is the entire outer surface surface of the quantum dot 16. On the other hand, the positions may be substantially uniform.

On the other hand, since the ligand 44 is soluble in the non-polar solvent 42, it remains in the non-polar solvent 42 even after the coordination bond with the quantum dot 16 is released. Therefore, the fifth liquid 54 becomes a solution in which the ligand 44 is dispersed in the non-polar solvent 42.

Since the non-polar solvent 42 and the non-aqueous polar solvent 20 have different polarities from each other, when the third liquid 50 is sufficiently allowed to stand, as shown in step S6B of FIG. The liquid 52 and the fifth liquid 54 are separated. Further, for example, when the specific gravity of the fifth liquid 54 is lighter than the specific gravity of the fourth liquid 52, the fifth liquid 54 is located at the upper part in the container 36 than the fourth liquid 52.

In general, quantum dots have the characteristic of photoexcited light emission, which is excited by absorbing light of a specific wavelength and emits light by the excitation. Therefore, by irradiating the third liquid 50 with an electromagnetic wave such as ultraviolet rays and causing the quantum dots 16 contained in the fourth liquid 52 to emit light, which of the two layers contained in the third liquid 50 is the fourth liquid 52? It is possible to judge.

Following step S6, the fourth liquid 52 is extracted from the third liquid 50 (step S8), and the extraction step is executed. As described above, in the third liquid 50 which has been sufficiently allowed to stand, the fourth liquid 52 and the fifth liquid 54 are separated. Therefore, it is possible to extract the fourth liquid 52 from the third liquid 50 by centrifuging the third liquid 50. As a result, the fourth liquid 52 in which the quantum dots 16 modified by the surface modification portion 18 are dispersed in the non-aqueous polar solvent 20 is generated as the quantum dot dispersion system. The fourth liquid 52 may contain the counter ions 48 contained in the second liquid 40.

<Formation of light emitting layer>
In the process of forming the light emitting layer 8 according to the present embodiment, the formation of the array substrate 3, the anode 4, and the hole transport layer 6 of the light emitting device 1 has been completed by the extraction step. In the step of forming the light emitting layer 8, following the take-out step, the fourth liquid 52 is applied onto the hole transport layer 6 and the fourth liquid 52 is dried (step S10).

For the application of the fourth liquid 52, various methods such as an inkjet method for applying a dispersion system of quantum dots can be adopted. The drying of the fourth liquid 52 is carried out to such an extent that the non-aqueous polar solvent 20 contained in the fourth liquid 52 remains in the vicinity of the outermost surface 16S of each quantum dot 16. In other words, even if the fourth liquid 52 is dried, the non-aqueous polar solvent 20 is retained between the non-volatile surface modifying portions 18 that modify each quantum dot 16, so that the quantum dots 16 The non-aqueous polar solvent 20 held in the vicinity of the outermost surface 16S does not volatilize.

Drying of the fourth liquid 52 may be carried out, for example, by allowing the laminate coated with the fourth liquid 52 to stand at a temperature of 60 ° C. or higher and 150 ° C. or lower for about 10 to 30 minutes. In particular, the fourth liquid 52 is preferably dried in an environment of 100 ° C. for about 10 minutes. Alternatively, the drying of the fourth liquid 52 may be carried out by allowing the laminate coated with the fourth liquid 52 to stand at room temperature.

With the above, the process of forming the light emitting layer 8 is completed. The light emitting layer 8 may contain counter ions 48 contained in the fourth liquid 52. After that, by forming the electron transport layer 10 and the cathode 12 in this order on the light emitting layer 8, the light emitting element 2 is formed, and the manufacturing process of the light emitting device 1 is completed.

<Selection of non-aqueous polar solvent based on the generation process of quantum dot dispersion system>
The specific configuration of the non-aqueous polar solvent 20 will be described based on the above-mentioned step of producing the fourth liquid 52, which is a quantum dot dispersion system.

In the step of producing the fourth liquid 52 according to the present embodiment, there is a step of dispersing the ligand 22 and the ionic liquid 30 in the non-aqueous polar solvent 20 to form the second liquid 40. Therefore, the non-aqueous polar solvent 20 may be any polar solvent in which the ligand 22 and the ionic liquid 30 can be dissolved.

Further, the fourth liquid 52 according to the present embodiment is a quantum dot dispersion system in which quantum dots 16 modified by the surface modification portion 18 are dispersed in a non-aqueous polar solvent 20. Therefore, the non-aqueous polar solvent 20 may be any polar solvent in which the quantum dots 16 modified by the surface modification portion 18 can be dissolved.

Therefore, as the non-aqueous polar solvent 20, at least one of a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether can be adopted.

For example, examples of materials that can be used as the non-aqueous polar solvent 20 include ethanol, propanol, and butanol as lower alcohols. Examples of the lower glycol include ethylene glycol. Examples of the lower glycol ester include propylene glycol monomethyl ether acetate (PMA). Examples of the lower glycol ether include propylene glycol 1-monomethyl ether 2-acetylate (PGMEA), propylene glycol monomethyl ether (PM), and ethylene glycol monomethyl ether.

In the present specification, "lower" means that the number of carbon atoms in one molecule is 2 or more and 8 or less. In particular, when the non-aqueous polar solvent 20 is a lower alcohol, in other words, when the number of carbon atoms in one molecule is 2 or more and 8 or less, the non-aqueous polar solvent 20 is a non-polar solvent 42. It has a sufficiently high polarity in comparison.

The boiling point of the non-aqueous polar solvent 20 may be 100 ° C. or higher. As a result, it is possible to reduce the volatilization of the non-aqueous polar solvent 20 held in the vicinity of the outermost surface 16S of the quantum dots 16 due to the heat generated by driving the light emitting element 2.

Further, the boiling point of the non-aqueous polar solvent 20 may be 200 ° C. or lower. Generally, when a layer containing quantum dots is formed by applying and drying a quantum dot dispersion system, the temperature of heating and drying of the quantum dot dispersion system should be up to about 150 ° C. in order to reduce deterioration of the quantum dots. May be restricted. In this case, if the boiling point of the non-aqueous polar solvent 20 is 200 ° C. or lower, the formation of the layer containing the quantum dots by heating and drying the quantum dot dispersion system containing the non-aqueous polar solvent 20 is performed by heating up to about 150 ° C. realizable. Therefore, when the boiling point of the non-aqueous polar solvent 20 is 200 ° C. or lower, the layer containing the quantum dots 16 from the solution in which the quantum dots 16 are dispersed in the non-aqueous polar solvent 20 while reducing the deterioration of the quantum dots 16. Needs to be formed more efficiently.

Further, the viscosity of the non-aqueous polar solvent 20 may be 0.5 mPa · s or more. As a result, a sufficient amount of the non-aqueous polar solvent 20 is retained in the vicinity of the outermost surface 16S of the quantum dots 16. Further, the viscosity of the non-aqueous polar solvent 20 may be 20 mPa · s or less. As a result, it becomes easier to apply the solution in which the quantum dots 16 are dispersed in the non-aqueous polar solvent 20, and the layer containing the quantum dots 16 can be formed more uniformly.

To exemplify some measured values of the viscosity of the material that can be used as the non-aqueous polar solvent 20, at 25 ° C., ethanol is 1.08 mPa · s, methanol is 0.54 mPa · s, PGMEA is 1.1 mPa · s, and isopropyl. Alcohol is 1.9 mPa · s. A falling ball viscometer: Lovis2000M / ME (manufactured by Anton Pearl Co., Ltd.) was used to measure the viscosities of these materials.

<Effect of quantum dot dispersion system>
The fourth liquid 52, which is the quantum dot dispersion system according to the present embodiment, contains the quantum dots 16 and the surface modification portion 18 containing the ligand 22 and the ionic liquid 30 in the non-aqueous polar solvent 20. Further, in the process of producing the fourth liquid 52, there is no process of directly exposing the quantum dots 16 to water. Therefore, it is possible to generate the fourth liquid 52, which is a quantum dot dispersion system including the surface modification portion 18, while reducing the deterioration of the quantum dots 16 due to moisture. Since the light emitting element 2 including the light emitting layer 8 formed from the fourth liquid 52 contains the quantum dots 16 with reduced deterioration, the luminous efficiency of the light emitting element 2 is improved.

In the process of producing the fourth liquid 52 according to the present embodiment, the solution containing the quantum dots 16 can be appropriately dehydrated. Specifically, for example, by dehydrating a solution containing 1 ml of a solvent containing quantum dots 16, the amount of water contained in the solution can be reduced to 1 μl or less.

Therefore, by the above dehydration treatment, the water content of the fourth liquid 52 can be set to 0% by volume or more and 0.1% by volume or less with respect to the total volume. With this configuration, the fourth liquid 52 can sufficiently reduce the deterioration of the dispersed quantum dots 16. Therefore, the water content of the light emitting layer 8 formed from the fourth liquid 52 is also 0% by volume or more and 0.1% by volume or less with respect to the total volume.

In the present embodiment, the quantum dot 16 holds the non-aqueous polar solvent 20 in the vicinity of the outermost surface 16S. Therefore, even when the moisture approaches the quantum dots 16, the outermost surface 16S of the quantum dots 16 is protected by the non-aqueous polar solvent 20. Therefore, the quantum dots 16 can reduce deterioration due to moisture even in the light emitting layer 8.

Other effects of the quantum dots 16 holding the non-aqueous polar solvent 20 in the vicinity of the outermost surface 16S will be described with reference to FIG. 7. FIG. 7 is another schematic enlarged view showing the same position as in FIG.

The coordination bond between the coordination functional group 24 of the surface modification portion 18 modified by the quantum dot 16 and the outermost surface 16S of the quantum dot 16 is a bond between the coordination functional group 24 and the carbon chain 26, or a quantum dot. It is a weak bond as compared with the bond between 16 molecules. Therefore, even after being formed as the light emitting layer 8, as shown in FIG. 7, the coordination bond between the coordination functional group 24 and the outermost surface 16S is broken, and the ligand 22 is the quantum dot 16. May be temporarily withdrawn from.

However, in the present embodiment, the quantum dot 16 holds the non-aqueous polar solvent 20 in the vicinity of the outermost surface 16S, and in particular, the ligand 22 is located inside the non-aqueous polar solvent 20. Therefore, even if the coordination bond between the coordination functional group 24 and the outermost surface 16S is temporarily broken, the ligand 22 does not immediately separate from the quantum dot 16 and is in the vicinity of the quantum dot 16. Stay in.

Therefore, the coordination between the coordination functional group 24 and the outermost surface 16S may be realized again while the ligand 22 remains in the vicinity of the quantum dot 16. Therefore, by holding the non-aqueous polar solvent 20 in the vicinity of the outermost surface 16S of the quantum dots 16, it is possible to reduce the complete detachment of the ligand 22 from the quantum dots 16, and thus the surface modification portion 18 It is possible to reduce the complete separation from the quantum dot 16.

〔Example〕
<Manufacturing of light emitting layer according to Examples>
The quantum dot dispersion system according to the embodiment is generated according to the method for generating the quantum dot dispersion system according to the present embodiment, and the light emitting layer 8 and the light emitting element 2 provided with the light emitting layer 8 are generated from the quantum dot dispersion system. Was manufactured and its characteristics were measured. The quantum dot dispersion system according to this embodiment was generated by the same method as the method for producing the fourth liquid 52 according to this embodiment. Further, the light emitting layer 8 according to the present embodiment was formed by the same method as the method for forming the light emitting layer 8 according to the present embodiment.

In step S2 according to this embodiment, the quantum dots 16 were dispersed in the non-polar solvent 42 so that the concentration of the quantum dots 16 was 20 mg / ml, and 200 μl of the first liquid 38 was produced. In this example, octane was used as the non-polar solvent 42, and quantum dots containing CdS having a core particle size of 2 nm were used as the quantum dots 16.

In step S4 according to this example, first, 200 μl of a solution in which the ionic liquid 30 was dispersed in the non-aqueous polar solvent 20 was produced so that the concentration of the ionic liquid 30 was 300 mg / ml. Next, a saturated solution in which the ligand 22 is dissolved in the non-aqueous polar solvent 20 is generated, the saturated solution is ultrasonically washed for 15 minutes, and then filtered through a 0.45 μm filter. A solution of the aprotic 22 was produced in an amount of 500 μl. Finally, the second liquid 40 was produced by mixing the solution of the ionic liquid 30 and the solution of the ligand 22.

In this example, PGMEA is added to the non-aqueous protic solvent 20, 2- (methacryloyloxy) -ethyltrimethylammonium bis (trifluoromethanesulfonyl) imide is added to the ionic liquid 30, and 2-diethylaminoethanethiol hydrochloride is added to the ligand 22. Adopted.

In step S6 according to this embodiment, the above-mentioned first liquid 38 and second liquid 40 were stirred at room temperature for 3 hours to generate a third liquid 50. In step S8 according to this embodiment, the third liquid 50 was extracted from the third liquid 52 by centrifuging the third liquid 50 at a rotation speed of 4000 rpm for 10 minutes. As a result, the fourth liquid 52, which is the quantum dot dispersion system according to the present embodiment, was generated.

By step S10 according to this embodiment, a laminate having the array substrate 3, the anode 4, and the hole transport layer 6 formed was prepared. In step S10 according to this embodiment, the fourth liquid 52 was applied onto the hole transport layer 6 of the laminate and dried at room temperature to obtain a light emitting layer 8. Then, the light emitting device 1 was manufactured through the formation of the electron transport layer 10 and the cathode 12 on the light emitting layer 8.

In order to evaluate the quantum dot dispersion system according to this example, the quantum dot dispersion system according to some comparative examples was manufactured, and the light emitting layer and the light emitting device were manufactured from the quantum dots.

The quantum dot dispersion system according to Comparative Example 1 was a solution in which the quantum dots used in the examples were dispersed in octane. The quantum dot dispersion system according to Comparative Example 2 was an aqueous quantum dot solution in which the quantum dots used in Examples and Comparative Example 1 were dispersed in water. In the quantum dot dispersion system according to Comparative Example 3, the ionic liquid obtained by stirring the quantum dot dispersion system according to Comparative Example 2 and the solution in which the ionic liquid is dispersed in PGMEA at room temperature for 3 hours is coordinated. A PGMEA solution in which the resulting quantum dots were dispersed was prepared.

The light emitting device according to each comparative example was manufactured by the same method as the light emitting device 1 according to the embodiment using the quantum dot dispersion system according to each comparative example.

It was found that the fluorescence quantum yield of the quantum dots contained in the quantum dot dispersion system according to Comparative Example 1 was about 40%. However, the ionic liquid is not coordinated with the quantum dots included in the quantum dot dispersion system according to Comparative Example 1. Therefore, the quantum dots included in the quantum dot dispersion system according to Comparative Example 1 are more likely to agglomerate than the quantum dots to which the ionic liquid is coordinated, which may cause a decrease in the reliability of the quantum dots. be.

Further, the fluorescence quantum yield of the quantum dots included in the quantum dot dispersion system according to Comparative Example 2 is about 1%, and the fluorescence quantum yield of the quantum dots included in the quantum dot dispersion system according to Comparative Example 3 is less than 1%. I found out. In Comparative Example 2 and Comparative Example 3, since the quantum dots are exposed to water in the step of replacing the ligands coordinated with the quantum dots with ionic liquids, the outermost surface of the quantum dots is deteriorated by the water, and the quantum dots are deteriorated. It is presumed that the fluorescence quantum yield of Therefore, the quantum dot dispersion system according to Comparative Example 3 has improved reliability of the quantum dots after film formation as compared with the quantum dot dispersion system according to Comparative Example 1, but the fluorescence quantum yield of the quantum dots is significantly reduced. do. Therefore, in the light emitting device including the light emitting layer formed from the quantum dot dispersion system according to Comparative Example 3, the external quantum efficiency may be significantly lowered.

It was found that the fluorescence quantum yield of the quantum dots 16 contained in the fourth liquid 52, which is the quantum dot dispersion system according to the example, was maintained at about 18%. In the first embodiment, in the step of generating the dispersion system of the quantum dots 16, it is not necessary to directly expose the quantum dots 16 to water, the deterioration of the outermost surface 16S of the quantum dots 16 is reduced, and the fluorescence quantum yield of the quantum dots 16 is reduced. It is presumed that the decrease in the rate has decreased.

The quantum dot 16 included in the fourth liquid 52, which is the quantum dot dispersion system according to the embodiment, includes the quantum dot 16 in which the ionic liquid 30 is coordinated and maintains a relatively high fluorescence quantum yield. Therefore, in the light emitting layer 8 formed from the fourth liquid 52 according to the embodiment, the aggregation of the quantum dots 16 is reduced, and the decrease in the luminous efficiency of the quantum dots 16 is reduced. Therefore, the light emitting device 1 provided with the light emitting layer 8 according to the embodiment further improves the light emitting efficiency and prolongs the life.

[Embodiment 2]
<Coordination part including anion part>
FIG. 8 is a schematic enlarged view showing the vicinity of the outermost surface 16S of the quantum dot 16 according to the present embodiment, and is an enlarged view showing a position corresponding to FIG. In this specification, each member having the same function is given the same name and reference numeral, and the same description will not be repeated unless there is a difference in configuration.

The light emitting device 1 according to the present embodiment has the same configuration as the light emitting device 1 according to the previous embodiment, except that the configuration of the surface modification portion 18 is different. In the present embodiment, as shown in FIG. 8, the ligand 22 contained in the surface modification portion 18 is the same as the ligand 22 according to the previous embodiment except that the anion portion 56 is included instead of the cation portion 28. It has the same configuration.

The anion portion 56 is a portion of the carbon chain 26 containing an anion formed at the end opposite to the coordination functional group 24. Therefore, in the ionic liquid 30, the cation portion 34 is bonded to the ligand 22 by forming an ionic bond with the anion portion 56 of the ligand 22. Except for the above points, the surface modification unit 18 according to the present embodiment has the same configuration as the surface modification unit 18 according to the previous embodiment.

A specific example of the surface modification portion 18 according to the present embodiment will be described with reference to FIG. In the present embodiment, the ligand 22 may be, for example, thioglycolic acid represented by the following chemical formula.

In this case, as shown in FIG. 9, the ligand 22 contains a sulfur atom in the coordination functional group 24 and a carboxylate anion in the anion portion 56.

Further, in the present embodiment, the material of the ionic liquid 30 may be appropriately changed according to the polarity of the ions possessed by the ligand 22. For example, in this embodiment, the ionic liquid 30 may be 1-benzyl-3-methylimidazolium tetrafluoroboric acid. In this case, the cation portion 34 of the ionic liquid 30 is, for example, 1-benzyl-3-methylimidazolium represented by the following chemical formula, and the cation 34C of the cation portion 34 shown in FIG. 5 is the anion of the ligand 22. It forms an ionic bond with part 56.

Further, the anion portion 32 of the ionic liquid 30 is, for example, tetrafluoroboric acid represented by the following chemical formula.

To further generalize the structure of the surface modification portion 18, for example, the ligand 22 may have a structure represented by the following chemical formula (2).

In the chemical formula (2), B represents the coordination functional group 24 and is selected from a thiol group, a carboxyl group, a phosphono group, or an amino group. n2 is a natural number representing the number of carbon atoms in the carbon chain 26 of the ligand 22, and is 1 or more and 3 or less. The range of n2 corresponds to the range in which the ligand 22 is soluble in a polar solvent.

The light emitting device 1 according to the present embodiment can be manufactured by the same method as the light emitting device 1 according to the previous embodiment. In particular, the light emitting layer 8 according to the present embodiment can be formed by the same method as the light emitting layer 8 according to the previous embodiment, except for the solute material of the second liquid 40 generated in step S4. In the present embodiment, the ligand 22 having the anion portion 56 is dispersed in the second liquid 40. The second liquid 40 may contain a counter ion, which is a cation that ionically bonds with the anion of the anion portion 56 of the ligand 22.

Also in this embodiment, for the same reason as described in the previous embodiment, the light emitting element 2 including the light emitting layer 8 includes the quantum dots 16 with reduced deterioration, so that the luminous efficiency of the light emitting element 2 is improved.

Further, as compared with the previous embodiment, the ligand 22 in the present embodiment has changed the polarity of the ion. Therefore, the surface modification portion 18 according to each of the previous embodiment and the present embodiment can select the ligand 22 containing more appropriate ions depending on the type of the ionic liquid 30 contained.

[Embodiment 3]
<Modification example of manufacturing method of quantum dot dispersion system>
The light emitting device 1 according to the present embodiment has the same configuration as the light emitting device 1 according to any of the above-described embodiments. The method for manufacturing the light emitting device 1 according to the present embodiment is the method for producing the light emitting device 1 according to any one of the above-described embodiments, except for the method for producing the fourth liquid 52, which is a quantum dot dispersion system used for forming the light emitting layer 8. It can be manufactured by the same method as the manufacturing method.

A method of forming the light emitting layer 8 of the light emitting device 1 according to the present embodiment will be described with reference to FIG. In this embodiment, as will be described in detail later, prior to the generation of the dispersion system of the quantum dots 16.
The sixth liquid and the seventh liquid are stirred to carry out the generation of the eighth liquid used for the generation of the dispersion system of the quantum dots 16. Regarding the method for forming the light emitting layer 8 according to the present embodiment, first, with reference to FIG. 11, which is a process cross-sectional view for explaining the stirring step of stirring the sixth liquid and the seventh liquid, the sixth liquid and the seventh liquid It will be explained together with the explanation of.

In the method for forming the light emitting layer 8 according to the present embodiment, first, the generation of the sixth liquid (step S12) and the generation of the seventh liquid (step S14) are executed. Next, the sixth liquid and the seventh liquid are stirred in the container 36 shown in FIG. 11 (step S16), and the stirring step is executed. Here, in step S16A of FIG. 11, the state immediately before starting the stirring of the sixth liquid 58 and the seventh liquid 60 injected into the container 36 in step S16 is shown.

As shown in step S16A of FIG. 11, the sixth liquid 58 is an aqueous solution in which a plurality of ligands 22 are dispersed in water 62. The ligand 22 may have, for example, the same configuration as the ligand 22 according to the first embodiment. The sixth liquid 58 may further contain counter ion 48, which is an anion that ionically bonds with the cation of the cation portion 28 of the ligand 22, in water 62. For example, specifically, the sixth liquid 58 may be a 500 μl aqueous solution containing 200 mg / ml of 2-diethylaminoethanethiol hydrochloride as the ligand 22.

The seventh liquid 60 is a solution in which the ionic liquid 30 is dispersed in the non-aqueous polar solvent 20 as shown in step S16A of FIG. The non-aqueous polar solvent 20 and the ionic liquid 30 may each have the same configuration as the non-aqueous polar solvent 20 and the ionic liquid 30 according to any of the above-described embodiments. For example, specifically, the seventh solution 60 contains 300 mg / ml of 2- (methacryloyloxy) -ethyltrimethylammonium bis (trifluoromethanesulfonyl) imide, which is an ionic liquid 30, in PGMEA, which is a non-aqueous polar solvent 20. It may be a 500 μl solution.

Since water 62 is a more polar solvent than the non-aqueous polar solvent 20, the sixth liquid 58 and the seventh liquid 60 are separated in the container 36. Further, for example, when the specific gravity of the 7th liquid 60 is lighter than that of the 6th liquid 58, the 7th liquid 60 is located at the upper part in the container 36 than the 6th liquid 58.

Stirring of the sixth liquid 58 and the seventh liquid 60 may be performed, for example, at room temperature for 1.5 hours. When the sixth liquid 58 and the seventh liquid 60 are stirred, the cation of the cation portion 28 of the ligand 22 and the anion of the anion portion 32 of the ionic liquid 30 are ionic bonded to form a surface modification portion. 18 is formed.

Step S16B of FIG. 11 shows the state in the container 36 after the sixth liquid 58 and the seventh liquid 60 are sufficiently stirred and then allowed to stand for a sufficient time. When the stirring of the sixth liquid 58 and the seventh liquid 60 is sufficiently performed, the eighth liquid 64 shown in step S6B of FIG. 11 is produced. The eighth liquid 64 contains the ninth liquid 66 and the tenth liquid 68.

Here, the ligand 22 may dissolve better in water 62 than in the non-aqueous polar solvent 20. Specifically, 2-diethylaminoethanethiol hydrochloride is more soluble in water than non-aqueous polar solvents such as PGMEA. In this case, a solution using water 62 as a solvent may obtain a solution having a higher concentration of the ligand 22 as compared with the non-aqueous polar solvent 20.

However, when the ionic liquid 30 dissolves better in the non-aqueous polar solvent 20 than in the water 62, the surface modification portion 18 formed by combining the ligand 22 and the ionic liquid 30 is compared with the water 62. In some cases, it dissolves better in the non-aqueous polar solvent 20. In this case, when the sixth liquid 58 and the seventh liquid 60 are stirred and the surface modification portion 18 is formed, more surface modification portions 18 are present in the non-aqueous polar solvent 20 as compared with the water 62. Will be done.

Therefore, when the stirring of the sixth liquid 58 and the seventh liquid 60 is sufficiently performed, as shown in step S6B of FIG. 11, the ninth liquid 66 containing the non-aqueous polar solvent 20 as a solvent is more water. The surface modification portion 18 having a higher concentration is dispersed than that of the tenth liquid 68 containing 62 as a solvent. From the above, the ninth liquid 66 in which the surface modification portion 18 is dispersed is generated in the non-aqueous polar solvent 20.

Following step S16, the ninth liquid 66 is extracted from the eighth liquid 64 (step S18). The ninth liquid 66 can be extracted by centrifuging the eighth liquid 64. In the present embodiment, the first liquid 38 is generated by the completion of step S18. The first liquid 38 may have the same configuration as the first liquid 38 according to the first embodiment, and the first liquid 38 may be generated by the same method as step S2 according to the first embodiment.

Next, a stirring step of stirring the extracted 9th liquid 66 with the 1st liquid 38 is executed (step S20). Step S20A of FIG. 12 shows a state immediately before starting stirring of the first liquid 38 and the ninth liquid 66.

The only difference between step S6 according to the first embodiment and step S20 according to the present embodiment is whether the solution to be agitated with the first liquid 38 is the second liquid 40 or the ninth liquid 66. be. The only difference between the second liquid 40 and the ninth liquid 66 is whether or not the ligand 22 dissolved in the non-aqueous polar solvent 20 and the ionic liquid 30 have already formed the surface modification portion 18. Is.

Step S20B of FIG. 12 shows the state in the container 36 after the first liquid 38 and the ninth liquid 66 are sufficiently stirred and then allowed to stand for a sufficient time. From the above circumstances, by stirring the first liquid 38 and the ninth liquid 66, as shown in step S20B of FIG. 12, a solution having the same configuration as the third liquid 50 according to the first embodiment can be obtained. Therefore, in step S20, the fourth liquid 52, which is the quantum dot dispersion system according to the present embodiment, is generated.

After that, the light emitting layer 8 according to the present embodiment is formed by sequentially executing the same steps as step S8 and step S10 according to the first embodiment.

Also in the present embodiment, for the same reason as described in each of the above-described embodiments, the light emitting element 2 including the light emitting layer 8 includes the quantum dots 16 with reduced deterioration, so that the luminous efficiency of the light emitting element 2 is improved. do.

Further, as compared with the method for producing the fourth liquid 52 according to each of the above-described embodiments, the ligand 22 is previously dispersed in water 62 and then combined with the ionic liquid 30 dispersed in the non-aqueous polar solvent 20. Therefore, there is a step of producing the ninth liquid 66 in which the ligand 22 is dispersed. With the above configuration, the ligand 22 and the ionic liquid 30 are more reliably bonded to form the surface modification portion 18, so that the surface modification portion 18 can modify the quantum dots 16 more efficiently.

Further, when the ligand 22 is more soluble in water 62 than the non-aqueous polar solvent 20, the concentration of the ligand 22 in the sixth liquid 58 is higher than the concentration of the ligand 22 in the second liquid 40 described above. Can also be increased. As a result, the concentration of the ligand 22 in the ninth liquid 66 can be increased, and thus the concentration of the surface modification portion 18 in the fourth liquid 52 can be increased.

However, although there is a step of dissolving the ligand 22 in water 62, also in this embodiment, the quantum dots 16 are directly exposed only to the non-aqueous polar solvent 20 or the non-polar solvent 42, and are exposed to water 62. There is no. Therefore, in the present embodiment, it is possible to reduce the deterioration of the quantum dots 16 contained in the fourth liquid 52 while increasing the concentration of the surface modification portion 18 in the fourth liquid 52.

[Embodiment 4]
<Polymerization of ionic liquids>
FIG. 13 is a schematic enlarged view showing the vicinity of the outermost surface 16S of the quantum dot 16 according to the present embodiment, and is an enlarged view showing the position corresponding to FIG. The light emitting device 1 according to the present embodiment has the same configuration as the light emitting device 1 according to the first embodiment, except that the configuration of the surface modifying portion 18 is different. In the present embodiment, the surface modification portion 18 has the same configuration as the surface modification portion 18 according to the first embodiment, except that the polymer 70 is included instead of the ionic liquid 30.

The polymer 70 is formed by polymerizing a plurality of surface modification portions 18 coordinated to the same quantum dot 16. In particular, the polymer 70 is a polymer formed by polymerizing a plurality of ionic liquids 30 according to each of the above-described embodiments between the anion portions 32 and the cation portions 34. For example, the polymer 70 is produced by performing heat treatment or ultraviolet irradiation on an ionic liquid 30 in which the anion portion 32 or the cation portion 34 has a polymerizable functional group to generate a polymerization reaction.

Therefore, the polymer 70 includes a plurality of anion portions 32 and a plurality of cation portions 34. In the present embodiment, as shown in FIG. 13, the anion of each anion portion 32 of the polymer 70 is bonded to the cation of the cation portion 28 of the ligand 22, thereby forming the surface modification portion 18. There is.

For example, in the present embodiment, it is assumed that the polymer 70 is generated from the ionic liquid 30 in which the cation portion 34 has a polymerizable functional group. In this case, the cation portion 34 may contain 2- (methacryloyloxy) -ethyltrimethylammonium as described above. In other words, the cation portion 34 may have a metachloro group as a polymerizable functional group. In this case, the cation portion 34 of the polymer 70 has a structure represented by the following chemical formula by polymerizing the cation portions 34 with each other.

In the above chemical formula, n3 is a natural number and indicates the degree of polymerization of the cation portion 34 of the polymer 70.

A method of forming the light emitting layer 8 of the light emitting device 1 according to the present embodiment will be described with reference to FIG. In the method of forming the light emitting layer 8 of the light emitting device 1 according to the present embodiment, steps S2 to S8 are executed by the same method as the manufacturing method of the light emitting device 1 according to the first embodiment.

In the method for forming the light emitting layer 8 according to the present embodiment, the polymerization initiator is added to the fourth liquid 52 following the formation of the fourth liquid 52 (step S22). The polymerization initiator added to the fourth liquid 52 may be appropriately selected from conventionally known polymerization initiators according to the type of the polymerizable functional group of the ionic liquid 30 contained in the fourth liquid 52.

Next, the fourth liquid 52 to which the polymerization initiator is added is applied onto, for example, the hole transport layer 6 (step S24). The coating of the fourth liquid 52 in the present embodiment may be carried out by the same method as the coating of the fourth liquid 52 in each of the above-described embodiments.

Next, the coated fourth liquid 52 is subjected to a treatment such as heat treatment or ultraviolet irradiation to polymerize the polymerizable functional groups contained in the ionic liquid 30 of the fourth liquid 52 (step S26). The treatment performed for the polymerization of the polymerizable functional groups of the ionic liquid 30 or the conditions of the treatment are appropriate depending on the type of the ionic liquid 30 or the type of the polymerizable functional groups contained in the ionic liquid 30. May be selected.

As a result, the ionic liquids 30 of the surface modification portion 18 coordinated to the quantum dots 16 are polymerized to form the polymer 70. Therefore, in the vicinity of the outermost surface 16S of the quantum dot 16, the quantum dot structure 14 in which the polymer 70 is coordinated via the ligand 22 is formed, and the light emitting layer 8 is formed.

Further, the surface modification portion 18 coordinated to the quantum dots 16 according to the present embodiment includes a polymer 70 derived from the ionic liquid 30. Therefore, even when the coordination bond between a certain quantum dot 16 and one of the plurality of ligands 22 included in the one surface modification portion 18 is broken, the quantum dot 16 and the other The probability that a coordinate bond with at least one of the ligands 22 of the above is maintained is improved. Therefore, it is possible to reduce that the surface modification portion 18 is completely separated from the quantum dots 16, the dispersibility of the quantum dots 16 can be further improved, and the aggregation of the quantum dots 16 can be reduced more efficiently.

[Embodiment 5]
<Wavelength conversion layer>
FIG. 15 is a schematic cross-sectional view of the light emitting device 72 according to the present embodiment. The light emitting device 72 according to the present embodiment includes a light source unit 74, a wavelength conversion layer 76 as an optical layer, and a light intensity control unit 78 in this order.

The light source unit 74 includes a light source that emits light to the wavelength conversion layer 76, which will be described later. The light source unit 74 may include a conventionally known light source including, for example, a blue light LED backlight, an ultraviolet light source, or the like. In addition, for example, the light source unit 74 may be a light emitting element 2 including the light emitting layer 8 according to each of the above-described embodiments.

The wavelength conversion layer 76 is an optical layer including a plurality of quantum dot structures 14 according to any of the above-described embodiments. The quantum dots 16 of the quantum dot structure 14 included in the wavelength conversion layer 76 absorb the light of a specific wavelength among the light emitted from the light source unit 74, so that the valence electrons of the semiconductor material in the quantum dots 16 are present. Banded electrons are excited to the conductive band. When the electron level returns from the conductive band to the valence band, light having a wavelength corresponding to the bandgap energy is emitted from the quantum dots 16. In order to obtain light emission from the quantum dots 16 by the above mechanism, it is necessary to irradiate the quantum dots 16 with light having an energy equal to or higher than the band gap energy of the semiconductor material in the quantum dots 16.

From the above mechanism, the wavelength conversion layer 76 absorbs at least a part of the light emitted from the light source unit 74 and irradiates the light having a specific wavelength longer than the light. In other words, the wavelength conversion layer 76 can be regarded as an optical layer that converts the wavelength of the irradiated light into a longer wavelength. Since the light from the light source unit 74 is converted into the light from the quantum dots 16 of the wavelength conversion layer 76, the light emitting device 1 can emit light having a narrow half-value width of the wavelength spectrum and a deep chromaticity.

The light intensity control unit 78 has a mechanism for controlling the intensity of light emitted from the wavelength conversion layer 76 toward the outside of the light emitting device 72. For example, the light intensity control unit 78 is provided with an anode 80, a liquid crystal layer 82, and a cathode 84 stacked in this order from the wavelength conversion layer 76 side. The light intensity control unit 78 changes the arrangement of the liquid crystals included in the liquid crystal layer 82 by changing the potential difference between the anode 80 and the cathode 84, and changes the transmittance of light from the wavelength conversion layer 76. As a result, the light intensity control unit 78 can control the intensity of the light emitted from the wavelength conversion layer 76 to the outside of the light emitting device 72.

The wavelength conversion layer 76 of the light emitting device 72 according to the present embodiment is coated with a solution containing the quantum dot structure 14 on the light source unit 74 by the same method as the method for forming the light emitting layer 8 according to each of the above-described embodiments. , Can be formed by drying. The light source unit 74 and the light intensity control unit 78 can be manufactured by a conventionally known manufacturing method.

Also in the present embodiment, for the same reason as described in each of the above-described embodiments, the wavelength conversion layer 76 including the light emitting layer 8 includes the quantum dots 16 with reduced deterioration, so that the wavelength conversion of the wavelength conversion layer 76 is performed. Efficiency improves.

Further, the light emitting device 72 may have a plurality of pixels having a plurality of sub-pixels, and each sub-pixel includes one laminated body 86 including a wavelength conversion layer 76 and a light intensity control unit 78. You may be. In this case, the wavelength conversion layers 76 included in the sub-pixels included in the same pixel may emit different wavelengths of light. Further, the light emitting device 72 may individually drive the light intensity control unit 78 provided in each sub-pixel. In this case, the light emitting device 72 can form a display device having a plurality of pixels.

In the present embodiment, the light emitting device 72 has a light intensity control unit 78, and controls the light emission intensity from the light emitting device 72 by controlling the intensity of the light transmitted through the light intensity control unit 78. explained. However, the present invention is not limited to this, and the light emitting device 72 does not necessarily have to include the light intensity control unit 78.

In this case, for example, in the light emitting device 72, a blue LED capable of controlling the light intensity for each sub-pixel may be formed in the light source unit 74. Alternatively, in the light emitting device 72, a blue light emitting element formed for each sub-pixel is formed in the light source unit 74, and the light from the blue light emitting element may be individually controlled. In this case, by controlling the intensity of the light from the light source unit 74 for each sub-pixel, the intensity of the light emitted to the wavelength conversion layer 76 and the intensity of the light emitted from the wavelength conversion layer 76 can be determined for each sub-pixel. Can be controlled to.

<Addendum>
In each of the above embodiments, the light emitting device 1 and the light emitting device 72 include a single light emitting layer 8 or a wavelength conversion layer 76. In other words, the light emitting device according to each of the above-described embodiments includes a single optical layer. However, the light emitting device according to each of the above-described embodiments is not limited to this, and may include, for example, a plurality of optical layers. In this case, at least one of the plurality of optical layers, the first optical layer, may have the same configuration as the light emitting layer 8 or the wavelength conversion layer 76 according to each of the above-described embodiments.

The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the claims, and the embodiments obtained by appropriately combining the technical means disclosed in the different embodiments. Is also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment.

1, 72 Light emitting device 2 Light emitting element 8 Light emitting layer 14 Quantum dot structure 16 Quantum dot 18 Surface modification part (coordinator)
20 Non-aqueous polar solvent 22 ligant 28 cation part 30 ionic liquid 38 first liquid 40 second liquid 42 non-polar solvent 50 third liquid 52 fourth liquid 56 anion part 66 ninth liquid 70 polymer 76 wavelength conversion layer

Claims

It contains (1) a first liquid containing a quantum dot and a non-polar solvent, and (2) a ligand, an ionic liquid, and a non-aqueous polar solvent that can be coordinated to the quantum dot and contains a cation or anion. A stirring step of stirring the second liquid and the solvent,
From the third liquid obtained by the stirring step, a take-out step of taking out the quantum dot, the coordination body containing the ligand and the ionic liquid, and the fourth liquid containing the non-aqueous polar solvent is performed. Includes
A method for producing a quantum dot dispersion system, wherein the non-aqueous polar solvent contains at least one of a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether.
The method for producing a quantum dot dispersion system according to claim 1, wherein the ionic liquid contains a polymerizable functional group.
The ionic liquid is
Bis (trifluoromethanesulfonyl) imide, thiosalicylic acid, tetrafluoroboric acid, hexafluorophosphate, dibutyl phosphate, acetic acid, disianamide, nitrate, hydrogen sulfate, octyl sulfate, methanesulfonic acid, thiosian acid, trifluoromethanesulfonic acid, amino With at least one of acetic acid and ethyl sulphate,
The production of the quantum dot dispersion system according to claim 1 or 2, which comprises at least one of an aliphatic quaternary ammonium ion, an imidazolium ion, a pyridinium ion, a phosphonium ion, a pyrrolidinium ion, a piperidinium ion, and a sulfonium ion. Method.
Quantum dots and
A coordinate body that can be coordinated to the quantum dot and
It comprises a non-aqueous polar solvent containing at least one of a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether.
A quantum dot dispersion system in which the water content is 0% by volume or more and 0.1% by volume or less with respect to the total volume.
The quantum dot dispersion system according to claim 4, wherein the boiling point is 100 ° C. or higher and 200 ° C. or lower.
The quantum dot dispersion system according to claim 4 or 5, wherein the viscosity is 0.5 mPa · s or more and 20 mPa · s or less.
The quantum dot dispersion system according to any one of claims 4 to 6, wherein the non-aqueous polar solvent contains a molecule having 2 or more and 8 or less carbon atoms.
At least one of a light emitting layer and a wavelength conversion layer that converts the wavelength of light emitted from a light source is provided as one or more optical layers.
Of the one or more optical layers, the first optical layer is
Quantum dots and
A coordinate body that can be coordinated to the quantum dot and
It comprises a non-aqueous polar solvent containing at least one of a lower alcohol, a lower glycol, a lower glycol ester, and a lower glycol ether.
A light emitting device having a water content of 0% by volume or more and 0.1% by volume or less with respect to the total volume of the first optical layer.