WO2023234074A1 - Nanoparticles, dispersion liquid, ink, thin film, organic light emitting diode, quantum dot display and method for producing nanoparticles - Google Patents

Abstract

The present invention provides nanoparticles which are configured from a metal oxide. With respect to the spectrum of the nanoparticles as measured by infrared spectrometry, if I1 is the maximum intensity assigned to a Zn-O-Zn bond within the range of 400 cm-1 to 600 cm-1, I2 is the maximum intensity assigned to a Zn-O-Si bond within the range of 870 cm-1 to 970 cm-1, and I3 is the maximum intensity assigned to an Si-O-Si bond within the range of 1,050 cm-1 to 1,150 cm-1, the peak intensity ratio I2/(I1 + I2 + I3) is 0.28 or more. The atomic ratio Zn/(Zn + Si) in the nanoparticles is within the range of 0.3 to 0.95; and the Scherrer diameter of the nanoparticles is within the range of 1 nm to 10 nm.

Description

Nanoparticles, dispersions, inks, thin films, organic light emitting diodes and quantum dot displays, and methods of manufacturing nanoparticles

The present invention relates to nanoparticles, dispersions, inks, thin films, organic light emitting diodes and quantum dot displays comprising such thin films, and methods for producing nanoparticles.

Organic light emitting diodes (OLEDs) and quantum dot (QD) displays are expected to be new light emitting devices, and some have been put into practical use.

In these devices, a light-emitting layer is placed between two electrodes (anode and cathode). When a voltage is applied between both electrodes, holes and electrons are injected from each electrode into the light emitting layer. When these holes and electrons are recombined within the luminescent layer, binding energy is generated, and the luminescent material in the luminescent layer is excited by this binding energy. Since light is emitted when the excited light-emitting material returns to its ground state, by utilizing this, light can be extracted to the outside.

In OLED and QD displays, to increase the luminous efficiency, a hole injection layer and/or hole transport layer is often installed between the anode and the emissive layer, and an electron injection layer and/or hole transport layer is installed between the emissive layer and the cathode. Or an electron transport layer is installed.

International Publication No. 2020/218354

In OLEDs, in order to reduce manufacturing costs and simplify the manufacturing process, the hole injection layer and/or hole transport layer on the anode, as well as the light emitting layer placed on top of the layer, are formed by a low-temperature process such as printing. It is proposed to do so.

However, in normal cases, the electron transport layer installed between the light emitting layer and the cathode is formed by a vapor deposition method. In order to further reduce manufacturing costs and simplify the process, it is considered effective to form the electron transport layer using a low-temperature process.

However, at present, there is a problem that it is difficult to form an electron transport layer by a printing method. This is because a material with a sufficiently low work function that can be formed into a film by a printing method and that can be applied to an electron transport layer has not been found.

Similarly, in QD displays, there is a need for a technology to form a film using a low-temperature process using a material with a sufficiently low work function that can be applied to the electron transport layer.

Note that Patent Document 1 describes that an aggregate containing Zn-Si-O nanoparticles with a low work function can be produced by a thermal plasma treatment method, and that an ink containing such an aggregate of nanoparticles is applied. It is described that a thin film for an electron transport layer of an OLED can be formed by this method.

However, thermal plasma treatment methods tend to produce nanoparticles with relatively large particle diameters. When such nanoparticles are applied to the electron transport layer of OLED and QD displays, there is a problem in that the surface of the electron transport layer becomes uneven. Irregularities on the surface of the electron transport layer can lead to scattering of light emitted from the light emitting layer. Further, at locations where the electron transport layer is thin, a problem may arise in that a current short circuit occurs between the light emitting layer and the cathode.

Therefore, there is a need for nanoparticles with smaller particle diameters that are less likely to cause the above-mentioned problems when applied to electron transport layers of OLED and QD displays.

The present invention was made in view of this background, and provides nanoparticles that have a low work function, can be applied to low-temperature film formation processes, and have a significantly small particle size. The purpose is to The present invention also aims to provide dispersions, inks, thin films containing such nanoparticles, organic light emitting diodes and quantum dot displays having such thin films, and methods for producing nanoparticles.

In the present invention, nanoparticles containing a metal oxide,
In the spectrum of the nanoparticles measured by infrared spectroscopy, the maximum intensity in the region of 400 cm ^-1 to 600 cm ^-1 derived from Zn-O-Zn bonds is defined as I ₁ , and the maximum intensity derived from Zn-O-Si bonds is defined as I 1. When the maximum intensity in the region of 870 cm ^-1 to 970 cm ^-1 is I ₂ and the maximum intensity in the region of 1050 cm ^-1 to 1150 cm ^-1 derived from Si-O-Si bonds is I ₃ , the peak intensity ratio I ₂ /(I ₁ +I ₂ +I ₃ ) is 0.28 or more,
The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
Nanoparticles are provided in which the Scherrer diameter of the nanoparticles is in the range of 1 nm to 10 nm.

Further, in the present invention, nanoparticles containing a metal oxide,
The average coordination number of the O atom closest to the Zn atom, determined by X-ray absorption fine structure (XAFS) analysis, is in the range of 3.0 to 4.5, and the X-ray absorption fine structure (XAFS) ) The average coordination number of the Zn atom closest to the Zn atom determined by analysis is in the range of 1.5 to 10,
The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
Nanoparticles are provided in which the Scherrer diameter of the nanoparticles is in the range of 1 nm to 10 nm.

Furthermore, the present invention provides a dispersion liquid containing nanoparticles having the above-mentioned characteristics, a solvent, and a dispersant.

Furthermore, the present invention provides an ink that includes nanoparticles having the above characteristics, a solvent, a dispersant, a thickener, and a surfactant.

The present invention also provides a thin film containing nanoparticles having the above-mentioned characteristics.

Furthermore, in the present invention,
comprising a first electrode, an organic light emitting layer, and a second electrode,
An organic light-emitting diode is provided, having an additional layer between the first electrode or the second electrode and the organic light-emitting layer, comprising a thin film having the above-mentioned characteristics.

Furthermore, in the present invention,
It has a first electrode, a quantum dot light emitting layer, and a second electrode,
A quantum dot display is provided, comprising an additional layer between the first electrode or the second electrode and the quantum dot emissive layer, comprising a thin film having the characteristics described above.

Furthermore, the present invention provides a method for producing nanoparticles containing metal oxides, comprising:
(1) mixing raw materials containing zinc and silicon with a first solvent to prepare a first solution;
(2) preparing a second solution containing an alkali;
(3) mixing the first solution and the second solution using a flow reactor method to generate a third solution containing nanoparticles;
(4) adding an additive that suppresses the growth of the nanoparticles to the third solution;
A method is provided having the following.

The present invention has a low work function, can be applied to a low-temperature film formation process, and can provide nanoparticles having a significantly small particle size. The present invention can also provide dispersions, inks, thin films containing such nanoparticles, organic light emitting diodes and quantum dot displays having such thin films, and methods for producing nanoparticles.

FIG. 2 is a diagram showing an example of an infrared spectrum of nanoparticles according to an embodiment of the present invention. FIG. 3 is a diagram showing an example of a Raman spectrum of nanoparticles according to an embodiment of the present invention. 1 is a diagram schematically showing an example of a flow of a method for manufacturing nanoparticles according to an embodiment of the present invention. 1 is a cross-sectional view schematically showing a configuration example of an OLED including nanoparticles according to an embodiment of the present invention. 1 is a cross-sectional view schematically showing a configuration example of a QD display including nanoparticles according to an embodiment of the present invention.

In one embodiment of the invention, nanoparticles comprising a metal oxide,
In the spectrum of the nanoparticles measured by infrared spectroscopy, the maximum intensity in the region of 400 cm ^-1 to 600 cm ^-1 derived from Zn-O-Zn bonds is defined as I ₁ , and the maximum intensity derived from Zn-O-Si bonds is defined as I 1. When the maximum intensity in the region of 870 cm ^-1 to 970 cm ^-1 is I ₂ and the maximum intensity in the region of 1050 cm ^-1 to 1150 cm ^-1 derived from Si-O-Si bonds is I ₃ , the peak intensity ratio I ₂ /(I ₁ +I ₂ +I ₃ ) is 0.28 or more,
The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
Nanoparticles are provided in which the Scherrer diameter of the nanoparticles is in the range of 1 nm to 10 nm.

As mentioned above, in OLED and QD displays, there is a need for a technology for forming a film using a low-temperature process using a material with a sufficiently low work function that can be applied to the electron transport layer.

In one embodiment of the present invention, the particles provided are in the form of nanoparticles, so that the nanoparticles are dispersed to prepare a dispersion, such as an ink, to form a film in a low-temperature process such as a printing method. Can be formed into a film.

Regarding a similar technique, Patent Document 1 describes Zn--Si--O nanoparticles produced by a thermal plasma method. It is described that these nanoparticles have a low work function, and that an electron transport layer of an OLED can be formed by applying an ink in which such nanoparticles are dispersed and forming a thin film.

However, the nanoparticles described in Patent Document 1 are manufactured by a thermal plasma method. The thermal plasma method has a problem in that the size of the nanoparticles produced, especially the upper limit of the particle diameter, is relatively large. In OLED and QD displays, the surface roughness of the electron transport layer can have a significant impact on the properties of the device. Therefore, it is preferable that the particle diameter of the nanoparticles be as small as possible.

In contrast, nanoparticles according to an embodiment of the present invention are produced by a method other than the thermal plasma method, for example, a liquid phase synthesis method.

The liquid phase synthesis method can provide nanoparticles whose Scherrer diameter is controlled within a microscopic range of 10 nm or less. Therefore, in one embodiment of the present invention, it is possible to form a thin film with significantly suppressed surface irregularities when applied as an electron transport layer of OLED and QD displays.

In general, liquid phase synthesis methods have a problem in that it is difficult to control the morphology of nanoparticles, especially the composition distribution within the particles. For example, when attempting to synthesize an oxide containing zinc and silicon from a solution containing a zinc source and a silicon source using a general liquid phase synthesis method, zinc oxide and silicon oxide separate, and the zinc oxide core Nanoparticles with silicon oxide surrounding them (core-shell structure) tend to be produced.

In the case of Zn--Si--O based oxide particles, a low work function is developed by converting zinc and silicon into a double oxide. Therefore, it is difficult to obtain a low work function with nanoparticles having a core-shell structure as described above.

On the other hand, in nanoparticles according to an embodiment _{of the present invention, the peak intensity ratio I 2 /} (I ₁ +I _{2 +} I ₃ ) is 0.28 or more. Here, the maximum intensity I ₁ corresponds to the Zn-O-Zn bond, the maximum intensity I ₂ corresponds to the Zn-O-Si bond, and the maximum intensity I ₃ corresponds to the Si-O-Si bond. .

That is, in the nanoparticles according to one embodiment of the present invention, the Zn--O--Si bond corresponding to the double oxide of zinc and silicon is significantly increased. Therefore, in one embodiment of the present invention, the work function of nanoparticles can be significantly reduced.

As a result of the above effects, one embodiment of the present invention has a low work function, can be applied to a low-temperature film formation process, and can provide nanoparticles having a significantly small particle size.

Further, in one embodiment of the present invention, nanoparticles containing a metal oxide,
The average coordination number of the O atom closest to the Zn atom, determined by X-ray absorption fine structure (XAFS) analysis, is in the range of 3.0 to 4.5, and the X-ray absorption fine structure (XAFS) ) The average coordination number of the Zn atom closest to the Zn atom determined by analysis is in the range of 1.5 to 10,
The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
Nanoparticles are provided in which the Scherrer diameter of the nanoparticles is in the range of 1 nm to 10 nm.

In one embodiment of the invention, Si is introduced into the nanoparticles.

At this time, the average coordination number of the O atom closest to the Zn atom is set in the range of 3.0 to 4.5, and the average coordination number of the Zn atom closest to the Zn atom is set in the range of 1.5 to 10. A suitable electron transport layer can be obtained by adjusting the amount within this range.

Note that the average coordination number of the O atom closest to the Zn atom and the average coordination number of the Zn atom closest to the Zn atom can be evaluated as described below using the XAFS analysis method.

In particular, in one embodiment of the present invention, the average coordination number of the O atom that is closest to the Zn atom is preferably 3.2 or more, from the viewpoint of suppressing coloring due to the generation of oxygen vacancies. It is more preferably .4 or more, and even more preferably 3.6 or more. Further, for example, the average coordination number of the O atom closest to the Zn atom is 4.4 or less, preferably 4.3 or less, from the viewpoint of increasing the band gap and obtaining high transparency.

Furthermore, in one embodiment of the present invention, the average coordination number of the Zn atom closest to the Zn atom is preferably 2.0 or more, and 2.5 or more, from the viewpoint of obtaining sufficient electrical conductivity. More preferably, it is 3.0 or more. In addition, the average coordination number of the Zn atom that is closest to the Zn atom is, for example, 9.0 from the viewpoint of reducing the spatial overlap between adjacent Zn4s orbitals and reducing the electron affinity and work function of the nanoparticle. It is preferably 8.0 or less, more preferably 7.0 or less, and even more preferably 6.0 or less.

Note that in the case of a ZnO single crystal, the average coordination number of the O atom closest to the Zn atom is 4, and the average coordination number of the Zn atom closest to the Zn atom is 12.

(Nanoparticles according to an embodiment of the present invention)
Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

Nanoparticles according to an embodiment of the present invention (hereinafter also simply referred to as "ZSO nanoparticles of the present invention") have a Zn--Si--O based oxide as a metal oxide.

The ZSO nanoparticles of the present invention have an atomic ratio of Zn/(Zn+Si) in the range of 0.3 to 0.95. When Zn/(Zn+Si) becomes lower than 0.3, the conductivity of the nanoparticles decreases. Furthermore, when Zn/(Zn+Si) exceeds 0.95, the work function of the nanoparticles increases. The lower limit of Zn/(Zn+Si) is preferably 0.6 or 0.7. In particular, Zn/(Zn+Si) is preferably in the range of 0.80 to 0.92.

Further, the Zn content in the ZSO nanoparticles of the present invention is 10% to 50% in terms of atomic concentration, preferably 31% to 47%, and more preferably 36% to 45%. The Si content in the ZSO nanoparticles of the present invention is 1% to 30% in terms of atomic concentration, preferably 2% to 13%, and more preferably 3% to 9%. The content of O in the ZSO nanoparticles of the present invention is 40% to 70% in terms of atomic concentration, preferably 50% to 62%, and more preferably 51% to 54%. If the contents of Zn, Si and O are within the above ranges, the nanoparticles will have high transparency and the display will have good light emitting characteristics.

Furthermore, the ZSO nanoparticles of the present invention may contain additives. As the additive, at least one selected from the group consisting of Al, Ga, Mg, Li, Ti, In, and N is preferable. By including such additives, the conductivity of the nanoparticles can be adjusted.

The content of additives in the ZSO nanoparticles of the present invention is 1% to 20%, preferably 5% to 15%, and more preferably 8% to 10% in terms of atomic concentration. If the content of the additive is within the above range, the composition in the nanoparticles will be homogeneous and the dispersibility will be good when dispersed in a solvent.

Furthermore, the ZSO nanoparticles of the present invention have a Scherrer diameter in the range of 1 nm to 10 nm. The Scherrer diameter is preferably in the range of 1 nm to 7 nm, more preferably in the range of 2 nm to 6 nm, even more preferably in the range of 3 nm to 5 nm.

If the Scherrer diameter is 10 nm or less, deterioration in flatness when forming a film is suppressed. Moreover, if the Scherrer diameter is 1 nm or more, the stability of the work function and electrical properties of the film increases.

In addition, in this application, the Scherrer diameter is determined from the diffraction peak in the powder X-ray diffraction results of the particles as shown in the following formula (1):

L=Kλ/(βcosθ) (1) Formula
Here, K is the Scherrer constant (=0.9), λ is the X-ray wavelength (=0.154 nm), θ is the peak position (=50 to 60°), and β is the peak half width.

The ZSO nanoparticles of the present invention have a band gap in the range of 3.1 eV to 3.9 eV. Preferably, the band gap is in the range of 3.2 eV to 3.8 eV.

If the band gap is 3.1 eV or more, the electron transport layer will have high transparency. Moreover, if the band gap is 3.9 eV or less, the electrical conductivity of the ZSO nanoparticles will be sufficient.

Note that the band gap of ZSO nanoparticles can be determined from the light transmission spectrum obtained using an ultraviolet-visible spectrophotometer.

The ZSO nanoparticles of the present invention have an ionization potential in the range of 6.0 eV to 8.0 eV. Preferably, the ionization potential is in the range of 6.5 eV to 7.5 eV.

If the ionization potential is 6.0 eV or more, the ZSO nanoparticles will have sufficient electrical conductivity. Moreover, if the ionization potential is 8.0 eV or less, electron injection into the light emitting layer will be good.

Note that the ionization potential of ZSO nanoparticles can be determined by ultraviolet photoelectron spectroscopy (UPS).

The ZSO nanoparticles of the present invention have an electron affinity in the range of 2.5 eV to 4.0 eV. Preferably, the electron affinity is in the range of 3.0 eV to 3.8 eV.

If the electron affinity is 2.5 eV or more, the ZSO nanoparticles will have sufficient electrical conductivity. Further, if the electron affinity is 4.0 eV or less, the electron injection property into the light emitting layer will be good.

Note that the electron affinity of the ZSO nanoparticles can be determined by subtracting the band gap value from the ionization potential value.

FIG. 1 shows an example of an infrared spectrum of ZSO nanoparticles of the present invention. In FIG. 1, for comparison, the spectrum of the SiO ₂ sample, the spectrum of the ZnO sample, and the spectrum of the ZnSi ₂ O ₄ sample are shown simultaneously. Note that in FIG. 1, the intensity on the vertical axis increases toward the bottom.

In the spectrum of the ZnO sample, a large absorption peak (referred to as "Zn--O--Zn bond peak") appears at a wave number of approximately 410 cm.sup. ^-1 . Furthermore, in the spectrum of the ZnSi ₂ O ₄ sample, a large absorption peak (referred to as "Zn--O--Si bond peak") appears at a wave number of about 920 cm ^-1 . Furthermore, in the spectrum of the SiO ₂ sample, a large absorption peak (referred to as "Si-O-Si bond peak") appears at a wave number of approximately 1070 cm ^-1 .

Therefore, in the spectrum obtained from the Zn-Si-O-based oxide sample, the infrared spectra occurring in the wavenumber range of 400 cm ^-1 to 600 cm ^-1 (referred to as region Q ₁ ) are Zn-O-Zn The infrared spectra generated in the range of wave numbers 870 cm ^-1 to 970 cm ^-1 (referred to as region Q ₂ ), which corresponds to the bond peak, correspond to the Zn-O-Si bond peak and wave numbers 1050 cm ^-1 to 1150 cm ^- It can be said that the infrared spectra generated in the range ^Q1 (referred to as region _Q3 ) corresponds to the Si-O-Si bond peak.

Here, as shown in FIG. 1, the infrared spectra of the ZSO nanoparticles of the present invention have the maximum intensity in region Q ₁ as I ₁ , the maximum intensity in region Q ₂ as I ₂ , and the maximum intensity in region Q ₃ . When the intensity is I ₃ , the peak intensity ratio I ₂ /(I ₁ +I ₂ +I ₃ ) is characterized by being 0.28 or more.

That is, the ZSO nanoparticles of the present invention have a high proportion of Zn--O--Si bonds corresponding to the double oxide of zinc and silicon, and therefore the work function can be significantly reduced.

In particular, the peak intensity ratio I ₂ /(I ₁ +I ₂ +I ₃ ) is preferably 0.29 or more, more preferably 0.30 or more, and even more preferably 0.31 or more. In this case, the work function of the ZSO nanoparticles of the present invention can be further reduced.

Note that the work function of the ZSO nanoparticles of the present invention is 3.9 eV or less. The work function is preferably 3.8 eV or less.

FIG. 2 shows an example of the Raman spectrum of the ZSO nanoparticles of the present invention. In FIG. 2, the spectrum of the SiO ₂ sample, the spectrum of the ZnO sample, and the spectrum of the Zn ₂ SiO ₄ sample are shown simultaneously for comparison. Note that in FIG. 2, the intensity on the vertical axis increases toward the top.

From FIG. 2, in the ZnO sample, multiple sharp peaks are observed in the wave number region of approximately 350 cm ⁻¹ to 450 cm ⁻¹ . On the other hand, it can be seen that in the ZSO nanoparticles of the present invention, the intensity peak in the same region is unified and the steepness of the peak is weakened compared to the ZnO sample.

From this, it is considered that the ZSO nanoparticles of the present invention exist in the state of a double oxide in which zinc oxide and silicon oxide are mixed at the atomic level.

(Method for producing nanoparticles according to an embodiment of the present invention)
Nanoparticles according to an embodiment of the present invention can be produced, for example, by a liquid phase synthesis method.

Hereinafter, with reference to FIG. 3, an example of a method for manufacturing nanoparticles according to an embodiment of the present invention will be described. FIG. 3 schematically shows an example of a flow of a method for producing nanoparticles according to an embodiment of the present invention.

As shown in FIG. 3, the method for producing nanoparticles according to one embodiment of the present invention (hereinafter referred to as the "first method") is as follows:
(1) mixing raw materials containing zinc and silicon with a first solvent to prepare a first solution (step S110);
(2) preparing a second solution containing an alkali (step S120);
(3) mixing the first solution and the second solution using a flow reactor method to generate a third solution containing nanoparticles (step S130);
(4) adding a particle growth inhibitor to the third solution (step S140);
has.

Hereinafter, each step will be explained in more detail.

(Step S110)
First, raw materials containing a zinc source and a silicon source are prepared.

The raw materials may be prepared in liquid form.

The zinc source may be a zinc compound, such as, for example, zinc oxide, zinc acetate, zinc nitrate, zinc carbonate, zinc chloride, zinc sulfate, and zinc alkoxide.

The silicon source may also be silicon compounds such as H ₂ SiO ₃ (silicic acid) and silicates. The silicon source may be, for example, a silicon oxide or hydroxide, other silicates, silicon compounds such as alkoxides, or hydrates thereof. Alkoxysilane silicon sources include dimethyldimethoxysilane (DMDMS), methyltrimethoxysilane (MTMS), tetramethoxysilane (TMOS), dimethyldiethoxysilane (DMDES), methyltriethoxysilane (MTES), and tetraethoxysilane. Examples include silane (TEOS). Also, oligomeric condensates of TEOS, such as ethyl silicate, may be used.

Next, the raw material is mixed with a first solvent to prepare a first solution.

The first solvent is not particularly limited as long as it can sufficiently dissolve and mix the raw materials.

The first solvent may be, for example, a dimethyl sulfoxide (DMSO) solvent.

The first solution is prepared so that the atomic ratio of zinc and silicon contained is Zn/(Zn+Si) of 0.3 to 0.95.

(Step S120)
Next, a second solution is prepared.

The second solution is an alkaline solution, such as at least one selected from lithium hydroxide, sodium hydroxide, potassium hydroxide, tetramethylammonium (TMAH), tetraethylammonium (TEAH), and ammonia ( _NH3 ). It may have one. Alternatively, the second solution may be a metal alkoxide such as sodium ethoxide.

(Step S130)
Next, the first solution and the second solution are mixed. This causes a reaction in which zinc and silicon bond together in the liquid, forming a third solution containing nanoparticles.

Note that it is difficult to produce the ZSO nanoparticles of the present invention using a general method of stirring and mixing two solutions using a container such as a beaker. This is because the zinc oxide and silicon oxide that reacted in the liquid separate from each other. In this case, particles with a so-called core-shell structure in which silicon dioxide is arranged around a zinc oxide core are easily obtained.

Therefore, in the first method, a flow reactor method is used in order to form a double oxide in which zinc oxide and silicon oxide are sufficiently mixed with each other.

In the flow reactor method, two disks are stacked one above the other, and a minute reaction field (thickness on the order of μm) is provided between the two disks. Further, the first liquid and the second liquid are respectively supplied from different ports provided on the upper disk.

At least one of the two discs is rotating at high speed, and the supplied first liquid and second liquid are supplied to a reaction field rotating at high speed, where a reaction occurs.

Thereafter, the reaction products (particulate products) are discharged from the system of the apparatus together with the residual liquid due to the centrifugal force of the rotation of the disk.

In the flow reactor method, the first liquid and the second liquid can be sufficiently mixed within a narrow reaction field by increasing the rotational speed of the circular disk. As a result, the plurality of generated phases becomes difficult to separate, and more homogeneous fine particles can be obtained.

Therefore, in the first method, it is possible to produce nanoparticles containing a double oxide in which zinc oxide and silicon oxide are sufficiently mixed with each other, rather than particles with a core-shell structure.

The supply temperatures of the first liquid and the second liquid are not particularly limited. The temperature of the first liquid and the second liquid is, for example, in the range of 20°C to 120°C, preferably in the range of 50°C to 90°C.

After step S130, a third solution containing nanoparticles is generated.

Thereafter, the third solution may be filtered to recover the nanoparticles, if necessary.

(Step S140)
In the first method, desired nanoparticles can be manufactured in the process of steps S110 to S130 described above.

However, if the third solution is left as is, there is a risk that the nanoparticles contained in the third solution will continue to grow and become coarse.

Therefore, after step S130, a particle growth inhibitor is added to the third solution.

The type of particle growth inhibitor is not particularly limited as long as it is a substance that can suppress the grain growth of nanoparticles.

Particle growth inhibitors include, for example, ethyl acetate, butyl acetate, benzene, toluene, xylene, chlorobenzene, dichlorobenzene, dichloromethane, chloroform, carbon tetrachloride, 1,2-dichloroethane, diethyl ether, methyl tert-butyl ether (MTBE), It may be selected from diisopropyl ether, diphenyl ether, 1,4-dioxane, tetrahydrofuran (THF).

By adding a particle growth inhibitor to the third solution, the growth of the formed nanoparticles is inhibited, and as a result, nanoparticles with a maximum Scherrer diameter of 10 nm or less are obtained.

Thereafter, the nanoparticles may be classified if necessary.

Through the above steps, the ZSO nanoparticles of the present invention can be manufactured.

(Application example of nanoparticles according to an embodiment of the present invention)
Next, an application example of nanoparticles according to an embodiment of the present invention having the above-mentioned characteristics will be described.

(Dispersion liquid)
Nanoparticles according to one embodiment of the invention can be provided, for example, in the form of a dispersion.

A dispersion can be prepared by dispersing nanoparticles in a solvent containing a dispersant.

It is preferable to use a polar solvent as the solvent because it makes it difficult to dissolve the organic light-emitting layer of the OLED and reduces damage to the interface. Examples of polar solvents that can be used include water, alcohols, glycols, glycol ethers, glycerin, and/or ethers.

Alcohols, glycols, glycol ethers, or ethers include, for example, the following compounds:
(i) Alcohols include methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-ethyl-1-butanol, isoamyl alcohol, 2-methyl-1 -butanol, 2-methyl-2-butanol, 3-methyl-2-butanol, 3-methoxybutanol, pentyl alcohol, 1-hexanol, 1-octanol, 1-pentanol, tert-pentyl alcohol and the like.
(ii) Glycols include ethylene glycol, diethylene glycol, propylene glycol, 1,3-propanediol, triethylene glycol, dimethyldiethylene glycol, dipropylene glycol, and the like.
(iii) Glycol ethers include ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monoisobutyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monophenyl ether, ethylene glycol butyl ethyl ether, and ethylene glycol Butyl methyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, ethylene glycol monomethyl ether acetate, ethylene glycol monoethyl ether acetate, propylene glycol mono t-butyl ether, propylene glycol monomethyl ether, propylene glycol monoethyl ether, propylene glycol monobutyl ether, Propylene glycol monopropyl ether, propylene glycol monoisopropyl ether, propylene glycol monoisobutyl ether, propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monopropyl ether, diethylene glycol diethyl ether, diethylene glycol Monobutyl ether, diethylene glycol dibutyl ether, diethylene glycol hexyl ether, diethylene glycol methyl t-butyl ether, diethylene glycol monoethyl ether acetate, diethylene glycol butyl ether acetate, dipropylene glycol methyl ether, dipropylene glycol mono-n-butyl ether, dipropylene glycol mono-n-propyl ether, Examples include dipropylene glycol monomethyl ether acetate.

As other solvents, N-methylformamide, N-methylpyrrolidone, dimethyl sulfoxide, fluorinated alcohol-based solvents, or glycol dialkyl ether-based solvents may be used.

These solvents may be used alone or in combination.

These solvents are insoluble in the organic light emitting layer in the OLED. Therefore, when an electron injection layer/electron transport layer containing nanoparticles is formed on the organic light emitting layer of an OLED using a dispersion containing these solvents, damage to the organic light emitting layer is reduced.

However, when using a dispersion containing nanoparticles for other purposes, a nonpolar solvent such as water, acetone, benzene, toluene, xylene, and/or hexane can also be used as the solvent.

The amount of nanoparticles contained in the dispersion may range, for example, from 0.01% to 50% by weight, and the amount of solvent may range from 50% to 99.9% by weight, for example. .

The dispersant is not particularly limited, but a polymeric dispersant, a surfactant type (low molecular type) dispersant, an inorganic type dispersant, etc. can be used. Examples of polymer dispersants include polycarboxylic acid polymer dispersants, polyamine polymer dispersants, acrylic polymer dispersants, urethane polymer dispersants, acrylic block copolymer polymer dispersants, and polyether polymer dispersants. Examples include a similar dispersant, a polyester polymer dispersant, polyethyleneimine, polyethyleneimine ethoxylate, and the like. Examples of surfactant-type dispersants include anionic surfactants such as carboxylates, sulfonates, sulfuric acid ester salts, and phosphoric acid ester salts, cationic surfactants such as amine salts and quaternary ammonium, and fatty acid esters. Any of the nonionic surfactants can be used. In addition, aminoethanols such as monoethanolamine, diethanolamine, triethanolamine, 2-amino 1,3-propanediol, thiols, organic sulfur compounds such as disulfides, methoxyacetic acid (MA), 2-methoxyethoxy Acetates such as acetic acid (MEA), 2-(2-methoxyethoxy)ethoxyacetic acid, (MEEA), and 2-ethoxyacetic acid can also be suitably used. As the inorganic dispersant, silane coupling agents, titanate coupling agents, aluminum coupling agents, etc. can also be used.

The amount of dispersant contained in the dispersion is, for example, in the range of 1.0% by mass to 4.0% by mass.

(ink)
Although in the form of a dispersion as described above, nanoparticles according to an embodiment of the invention may be prepared in the form of an ink.

The ink is prepared by dispersing nanoparticles in one or more solvents that include a dispersant, an image tackifier, and a surfactant.

One or more solvents may be selected from the candidates listed as solvents for the dispersion liquid described above.

In order to prevent clogging of the inkjet head, the solvent is preferably one that is difficult to volatilize at the nozzle portion and has a boiling point of 180° C. or higher. Such solvents include, for example, ethylene glycol, diethylene glycol (DEG), propylene glycol, and dipropylene glycol (DPG).

These solvents are characterized by high dispersibility of the ZSO nanoparticles of the present invention.

In addition, when an ink containing these solvents is used to form an electron injection layer/electron transport layer on an organic light-emitting layer of an OLED or a quantum dot (QD) light-emitting layer of a QD display, the organic light-emitting layer or QD light-emitting layer The damage dealt is reduced.

As the dispersant, the above-mentioned dispersants can be used.

Thickeners may include propylene glycol, terpineol and ethylcellulose. Further, as another additive, a transparent conductor (indium tin oxide) for adjusting the conductivity of the ink, aluminum-doped zinc oxide (AZO), and/or carbon black may be used.

The dispersant, image tackifier, and surfactant may be contained in the entire ink at a concentration of 10% by mass or less, for example.

The viscosity of the ink is preferably 1 to 50 mPa·s (CP). In particular, when used for inkjet printing, the viscosity of the ink is preferably 5 to 20 mPa·s (CP). Furthermore, particularly when used for inkjet printing, it is more preferable that the ink has a viscosity of 8 to 15 mPa·s (CP).

Furthermore, the ink preferably has a low water content, and therefore it is preferable to dehydrate the ink before use. The dehydration method is not particularly limited, but molecular sieves, anhydrous sodium sulfate, and/or calcium hydroxide can be used. The moisture content of the ink is preferably 0.1% by mass or less.

Furthermore, the ink may contain an alkali metal complex, an alkali metal salt, an alkaline earth metal complex, or an alkaline earth metal salt.

By using such an ink, an electron injection layer/electron transport layer containing an alkali metal or alkaline earth metal complex or salt can be formed by a printing process. By containing an alkali metal or alkaline earth metal complex or salt, electron injection efficiency can be further improved.

It is preferable that the alkali metal or alkaline earth metal complex or salt is soluble in the solvent of the ink. Alkali metals include lithium, sodium, potassium, rubidium, and cesium. Alkaline earth metals include magnesium, calcium, strontium, and barium. Complexes include β-diketone complexes, and salts include alkoxides, phenoxides, carboxylates, carbonates, and hydroxides.

Specific examples of complexes or salts of alkali metals and alkaline earth metals include sodium acetylacetonate, cesium acetylacetonate, calcium bisacetylacetonate, barium bisacetylacetonate, sodium methoxide, sodium phenoxide, and sodium tert-butoxide. , sodium tert-pentoxide, sodium acetate, sodium citrate, cesium carbonate, cesium acetate, sodium hydroxide, and cesium hydroxide.

(OLED)
Nanoparticles according to an embodiment of the present invention can be used in thin films of various devices and the like. For example, nanoparticles according to an embodiment of the present invention can be applied to the electron injection layer/electron transport layer of an OLED.

FIG. 4 schematically shows a cross section of an OLED to which nanoparticles according to an embodiment of the present invention are applied.

As shown in FIG. 4, the OLED 100 includes a substrate 110, a bottom electrode (anode) 120, a hole injection layer/hole transport layer 130, an organic light emitting layer 140, an additional layer 150, and a top electrode (cathode) 160. , and an insulating layer 170.

In the OLED 100, when the substrate 110 and the bottom electrode 120 are made of a transparent material, the OLED 100 becomes a bottom emission type in which the substrate 110 side becomes the light extraction surface. On the other hand, in the OLED 100, when the upper electrode 160 is made of a transparent material or a semi-transparent material and the lower side of the bottom electrode 120 is made of a reflective layer, the top emission type in which the upper electrode 160 side becomes the light extraction surface. becomes.

The substrate 110 has the role of supporting each layer installed thereon.

Further, when the substrate 110 side is used as a light extraction surface (bottom emission type), the bottom electrode 120 is made of a conductive metal oxide such as indium tin oxide (ITO), for example. On the other hand, the upper electrode 160 is made of metal or semiconductor, for example. The hole injection layer/hole transport layer 130 is made of a hole transporting compound. The hole transporting compound is preferably a compound having an ionization potential of 4.5 eV to 6.0 eV from the viewpoint of a charge injection barrier from the anode to the hole injection layer.

Examples of hole-transporting compounds include aromatic amine compounds, phthalocyanine compounds, porphyrin compounds, oligothiophene compounds, polythiophene compounds, benzylphenyl compounds, compounds in which tertiary amines are linked with fluorene groups, and hydrazone compounds. compounds, silazane-based compounds, quinacridone-based compounds, and the like.

Among the above-mentioned exemplary compounds, aromatic amine compounds are preferred, and aromatic tertiary amine compounds are particularly preferred, in terms of amorphousness and visible light transparency. Here, the aromatic tertiary amine compound is a compound having an aromatic tertiary amine structure, and also includes a compound having a group derived from an aromatic tertiary amine.

The type of aromatic tertiary amine compound is not particularly limited, but a polymeric compound with a weight average molecular weight of 1,000 or more and 1,000,000 or less (a polymeric compound with a series of repeating units) is preferred, since it is easy to obtain uniform light emission due to the surface smoothing effect. It is preferable to use

The organic light-emitting layer 140 is made of an organic substance that emits red, green, and/or blue light, for example.

The organic light emitting layer 140 is a functional layer that has the function of emitting light (including visible light). The organic light emitting layer 140 is usually composed of an organic material that mainly emits at least one of fluorescence and phosphorescence, or this organic material and a dopant that assists the organic material. A dopant is added, for example, to improve luminous efficiency or change the emission wavelength. The organic substance may be a low molecular compound or a high molecular compound. The thickness of the emissive layer may be, for example, about 2 nm to 200 nm.

The insulating layer 170 is made of, for example, a photosensitive resin such as a fluororesin or a polyimide resin.

The hole injection layer/hole transport layer 130 and/or the organic light emitting layer 140 can be formed, for example, by a printing process.

Additional layer 150 includes ZSO nanoparticles of the present invention. For example, additional layer 150 may include a thin film comprising ZSO nanoparticles of the present invention.

Therefore, additional layer 150 has a relatively low work function and adequate electrical conductivity. For example, the work function of additional layer 150 is 3.9 eV or less. Further, the electrical conductivity of the additional layer 150 is, for example, 10 ⁻⁸ Scm ⁻¹ or more, for example, 10 ⁻⁵ Scm ⁻¹ or more.

Therefore, the additional layer 150 can function as an electron injection layer and/or an electron transport layer.

Further, the additional layer 150 can be formed using a low-temperature process such as a printing process. That is, the additional layer 150 can be formed on the organic light emitting layer 140 by preparing an ink as described above and performing a printing process using the ink.

As the printing process, for example, an inkjet printing method, a screen printing method, etc. can be used. In particular, when the additional layer 150 is installed by a printing process, the thickness can be more easily controlled than when the additional layer 150 is formed by a conventional vapor deposition method.

Note that in the OLED 100, the Scherrer diameter of the nanoparticles included in the additional layer 150 is in the range of 1 nm to 10 nm. When such fine nanoparticles are used, unevenness on the surface of the additional layer 150 can be significantly suppressed.

As a result, light emitted from the organic light emitting layer 140 of the OLED 100 is suppressed from being scattered by the additional layer 150. Additionally, the minimum thickness of the additional layer 150 is maintained, and the problem of current leakage between the organic light emitting layer 140 and the upper electrode 160 is significantly suppressed.

For example, the surface roughness RMS (root mean square height) of the additional layer 150 is 5 nm or less.

In the OLED 100, the hole injection layer/hole transport layer 130 to the additional layer 150 can be formed by a printing process.

In this case, the conventional vapor deposition equipment for forming the electron injection layer/electron transport layer is not required, and the equipment cost can be reduced. Therefore, OLED 100 can be easily manufactured at relatively low cost.

Furthermore, in the conventional configuration, when an upper electrode is placed on the organic electron injection layer/electron transport layer, there is a risk that the electron injection layer/electron transport layer may be damaged by heat. Therefore, there is a problem in that it is difficult to form the upper electrode 160 using a heat generation process such as sputtering.

However, in OLED 100, additional layer 150 includes nanoparticles having characteristics as described above. Therefore, the upper electrode 160 disposed on the additional layer 150 can be formed using a heat generation process such as sputtering, for example.

Note that the additional layer 150 may be composed of a multilayer of a thin film containing the ZSO nanoparticles of the present invention and other layers.

(QD display)
Nanoparticles according to an embodiment of the present invention can be applied to the electron injection layer/electron transport layer of a QD display.

FIG. 5 schematically shows a cross section of a QD display to which nanoparticles according to an embodiment of the present invention are applied.

As shown in FIG. 5, the QD display 200 includes a substrate 210, a bottom electrode (anode) 220, a hole injection layer/hole transport layer 230, a quantum dot (QD) light emitting layer 240, an additional layer 250, and a top It has an electrode (cathode) 260.

Among these, the description in the above-mentioned OLED 100 can be referred to for the substrate 210, the bottom electrode (anode) 220, the hole injection layer/hole transport layer 230, and the upper electrode (cathode) 260. Therefore, detailed explanation will be omitted here.

The QD light emitting layer 240 is composed of nanoparticles such as CdSe, ZnSe, InP, PbS, perovskite (CsPbX3; X is Cl, Br, or I).

Here, the additional layer 250 includes ZSO nanoparticles of the present invention.

Therefore, additional layer 250 has a relatively low work function and adequate electrical conductivity. For example, the work function of additional layer 250 is 3.9 eV or less. Further, the electrical conductivity of the additional layer 250 is, for example, 10 ⁻⁸ Scm ⁻¹ or more, for example, 10 ⁻⁵ Scm ⁻¹ or more.

Therefore, the additional layer 250 can function as an electron injection layer and/or an electron transport layer.

The additional layer 250 can be deposited using a low temperature process such as a printing process. That is, the additional layer 250 can be formed on the QD light emitting layer 240 by preparing an ink as described above and performing a printing process using the ink.

As the printing process, for example, an inkjet printing method, a screen printing method, etc. can be used. In particular, when the additional layer 250 is deposited by a printing process, the thickness can be more easily controlled than when deposited by a conventional vapor deposition method.

Note that in the QD display 200, the Scherrer diameter of the nanoparticles included in the additional layer 250 is in the range of 1 nm to 10 nm. When such fine nanoparticles are used, unevenness on the surface of the additional layer 250 can be significantly suppressed.

As a result, light emitted from the QD light emitting layer 240 of the QD display 200 is suppressed from being scattered by the additional layer 250. Additionally, the minimum thickness of the additional layer 250 is maintained, and the problem of current leakage between the QD light emitting layer 240 and the upper electrode 260 is significantly suppressed.

For example, the surface roughness RMS (root mean square height) of the additional layer 250 is 5 nm or less.

In this way, in the QD display 200, the hole injection layer/hole transport layer 230 to the additional layer 250 can be formed by a printing process.

Therefore, the QD display 200 can be easily manufactured at relatively low cost.

Additionally, in the QD display 200, the additional layer 250 includes nanoparticles having the characteristics described above. Therefore, the upper electrode 260 disposed on the additional layer 250 can be formed using a heat generation process such as a sputtering method.

Examples of the present invention will be described below.

In the following description, Examples 1 to 3 are examples, and Examples 11 to 13 are comparative examples.

(Example 1)
Nanoparticles were produced by the first method described above.

First, zinc acetate as a zinc source and tetraethoxysilane (TEOS) as a silicon source were added to dimethyl sulfoxide (DMSO) solvent at room temperature to prepare a first solution.

The concentration of zinc acetate in the first solution was 0.1 mol/L, and the concentration of TEOS was 0.038 mol/L. Therefore, the atomic ratio Zn/(Zn+Si) in the first solution is 0.725.

Next, tetraethylammonium hydroxide (TEAH: 20 vol%) was added to the DMSO solvent to prepare a second solution. The concentration of TEAH in the second solution was 5% by weight.

Thereafter, the first solution and the second solution were mixed using a flow reactor device.

The temperature of the first solution supplied was set in the range of 60°C to 70°C. The supply flow rate of the first solution was 43.6 mL/min, and the supply pressure was 0.1 to 0.2 MPaG. Similarly, the temperature of the second solution supplied was set in the range of 60°C to 70°C. The supply flow rate of the second solution was 26.4 mL/min, and the supply pressure was 0.1 to 0.2 MPaG. The rotation speed of the disk was 5000 rpm.

Note that the first solution was supplied to the flow reactor device 4 hours after it was prepared.

After supplying the first solution and the second solution, the reaction solution discharged from the flow reactor device was immediately poured into a container filled with ethyl acetate as a growth inhibitor to stop the reaction.

Thereafter, nanoparticles (hereinafter referred to as "nanoparticles 1") were collected by collecting and filtering the third solution discharged from the flow reactor device. The filtration method used a centrifuge to discard the supernatant liquid of the third solution and collect the precipitate. Further, the operation of diluting the precipitate with ethanol and then recovering the precipitate using a centrifuge was repeated three times.

(Example 2)
Nanoparticles were produced by a method similar to Example 1. However, in this Example 2, the flow rates of the first and second solutions supplied to the flow reactor device were changed. The supply flow rate of the first solution was 18.68 mL/min. The supply flow rate of the second solution was 11.32 mL/min.

As a result, nanoparticles (hereinafter referred to as "nanoparticles 2") were recovered.

(Example 3)
Nanoparticles were produced by a method similar to Example 1. However, in this Example 3, the flow rates of the first and second solutions supplied to the flow reactor device were changed. The supply flow rate of the first solution was 31.14 mL/min. The feed flow rate of the second solution was 18.86 mL/min. As a result, nanoparticles (hereinafter referred to as "nanoparticles 3") were recovered.

(Example 11)
Nanoparticles were produced using a beaker instead of a flow reactor device.

The above-described first solution and second solution were added into a beaker and thoroughly stirred at room temperature. The compositions of the first solution and the second solution are the same as in Example 1.
After 5 minutes, stirring was stopped and ethyl acetate was added to the beaker.

Thereafter, the nanoparticles (hereinafter referred to as "nanoparticles 11") were recovered by filtering the solution in the beaker.

(Example 12)
Nanoparticles were produced by a method similar to Example 1. However, in this Example 12, only zinc acetate and no tetraethoxysilane (TEOS) were added to the first solution.

As a result, nanoparticles (hereinafter referred to as "nanoparticles 12") were recovered.

(Example 13)
Nanoparticles were manufactured using a thermal plasma method as follows.

First, a raw material slurry was prepared. The raw material slurry was prepared by dispersing in alcohol a mixed powder obtained by mixing zinc oxide particles and silicon dioxide particles at a molar ratio of 60:40.

Next, a thermal plasma was generated within the reaction chamber. Thermal plasma was generated by applying a high frequency voltage between electrodes in a reaction chamber with a mixed atmosphere of argon and oxygen (Ar:O ₂ =80:20). The temperature of the thermal plasma was about 10,000K.

Next, the prepared raw material slurry was introduced into this thermal plasma.

The raw material slurry was turned into plasma by thermal plasma and turned into a gas phase. Thereafter, a mixed gas of nitrogen and oxygen (N ₂ :O ₂ =75:25) at room temperature was supplied to this gas phase to rapidly cool the gas phase.

As a result, nanoparticles (hereinafter referred to as "nanoparticles 13") were produced.

Table 1 below summarizes the manufacturing conditions for nanoparticles in each example.

(evaluation)
The following evaluations were performed using each of the manufactured nanoparticles.

(composition analysis)
The composition of each nanoparticle was analyzed using SEM-EDX.

A scanning electron microscope S4300 manufactured by Hitachi, Ltd. was used for the measurement. Further, as an EDX detector, an energy dispersive X-ray analyzer X-act manufactured by Oxford was used. At this time, the relative sensitivity coefficients of the measurement elements were calibrated in advance using standard samples, and measurement conditions were used in which the counts of each of O, Si, and Zn were 10,000 or more. Samples for measurement were prepared according to the following procedure. First, the nanoparticles were diluted with an ethanol solvent, and then a dispersion containing the nanoparticles was prepared. The concentration of nanoparticles was 3 wt%. Next, about 10 μL of the dispersion liquid was dropped onto an Al sample stand for SEM. Thereafter, by drying the ethanol at room temperature, the nanoparticles were supported on the sample stage to form a measurement sample.

As a result, it was found that for nanoparticles 1 to 3, the atomic ratio Zn/(Zn+Si) was all in the range of 0.3 to 0.95. On the other hand, in nanoparticles 11 to 12, the atomic ratio Zn/(Zn+Si) was approximately 1. Further, in nanoparticle 13, the atomic ratio Zn/(Zn+Si) was 0.75.

(Evaluation of Scherrer diameter)
An X-ray diffraction analysis of each nanoparticle was performed using an X-ray diffraction device (device name: D2 Phaser, manufactured by Bruker). From the obtained diffraction peak, the Scherrer diameter was calculated according to the above-mentioned formula (1).

As a result, it was found that Nanoparticles 1 to 3 all had Scherrer diameters in the range of 1 nm to 10 nm.

(Infrared spectroscopy)
Infrared spectroscopic analysis was performed using each nanoparticle. For the measurement, Nic-plan/Nicolet 6700 manufactured by Thermo Fisher Scientific was used.

As an example, the above-mentioned FIG. 1 shows an infrared spectrum of nanoparticles 2.

From FIG. 1, I ₂ /(I ₁ +I ₂ +I ₃ ) in nanoparticle 2 was calculated. As mentioned above, I ₁ is the maximum intensity in region Q ₁ , I ₂ is the maximum intensity in region Q ₂ , and I ₃ is the maximum intensity in region Q ₃ . As a result, I ₂ /(I ₁ +I ₂ +I ₃ )=0.383.

Note that similar infrared spectra were obtained for nanoparticles 1 and 3 as well.

(Raman spectroscopy)
Microscopic Raman spectroscopy was performed using each nanoparticle. For the measurement, LabRAM HR Evolution manufactured by Horiba, Ltd. was used.

As an example, the above-mentioned FIG. 2 shows the Raman spectrum of the nanoparticles 2.

From Figure 2, in nanoparticle 2, the multiple steep peaks observed in the wavenumber region of 300 cm ^-1 to 500 cm ^-1 in the ZnO sample disappear, and instead a single peak with a relatively wide half-width appears. I know that there is.

Note that similar Raman spectra were obtained for nanoparticles 1 and 3 as well.

(XAFS analysis)
Perform XAFS measurement using nanoparticles 1 to 3 to determine the average coordination number of the O atom closest to the Zn atom and the average coordination number of the Zn atom closest to the Zn atom. Ta. For the measurement, Aichi Synchrotron Optical Center BL11S was used.

For the XAFS measurement, a transmission step scan or QUICK XAFS method was used.

Each nanoparticle was diluted with boron nitride powder so that Δμt of the Zn K end was 1, and a pellet was produced by pressure molding. The prepared pellets were sealed in a plastic film and set in a measuring device.

The XAFS measurement was performed at room temperature, and the EXAFS vibration in k-space was extracted from the obtained XAFS spectrum, and the FT-EXAFS (radial distribution function) in R-space was obtained by Fourier transformation. The structural parameters of ZSO nanoparticles were calculated by EXAFS fitting analysis for R-space FT-EXAFS. Wurtzite type ZnO was used as the reference structure.

Table 2 below summarizes the evaluation results obtained for each nanoparticle.

As shown in Table 2, it was found that nanoparticles 1 to 3 had smaller particle sizes and relatively higher I ₂ /(I ₁ +I ₂ +I ₃ ) compared to nanoparticles 11 to 13. .

Furthermore, in nanoparticles 1 to 3, the average coordination number of the O atom closest to the Zn atom was found to be in the range of 3.0 to 4.5. Furthermore, it was found that in nanoparticles 1 to 3, the average coordination number of the Zn atom closest to the Zn atom was in the range of 1.5 to 10.

(Formation of thin film)
(Thin film 1)
A thin film was formed on a substrate using a dispersion containing nanoparticles 1.

The dispersion liquid was prepared as follows.

Nanoparticles 1 and monoethanolamine (MEA) were added to a propylene glycol solvent at room temperature, mixed thoroughly, and then treated with an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd.) at an output of 150 W for 30 minutes. The concentration of nanoparticles 1 was 3 wt%, and the concentration of MEA was 3 wt%. Furthermore, the obtained dispersion liquid was filtered using a filter with a hole diameter of 0.22 μm (Durapore manufactured by Merck & Co., Ltd.). As a result, a dispersion liquid (hereinafter referred to as "dispersion liquid 1") was prepared.

Next, Dispersion 1 was applied onto the substrate by a spin coating method to form a coating film. Thereafter, the coating film was baked at 150°C to form a thin film (hereinafter referred to as "thin film 1"). The thickness of the thin film 1 was targeted to be 40 nm.

Note that a silica glass substrate and an indium tin oxide (ITO) substrate were used as the substrates. Thin film 1 on the silica glass substrate was used for the flatness evaluation shown below, and thin film 1 on the ITO substrate was used for the work function evaluation.

(Thin film 2)
A dispersion containing nanoparticles 2 (hereinafter referred to as "dispersion 2") was prepared by diluting nanoparticles 2 with an ethanol solvent. The concentration of nanoparticles 2 was 3 wt%. A thin film was formed on an ITO substrate using Dispersion 2. The baking treatment temperature after spin coating was 100°C. The obtained thin film is referred to as "thin film 2."

(Thin film 3)
A dispersion containing nanoparticles 3 (hereinafter referred to as "dispersion 3") was prepared by diluting nanoparticles 3 with an ethanol solvent. The concentration of nanoparticles 3 was 3 wt%. A thin film was formed on an ITO substrate using dispersion liquid 3. The baking treatment temperature after spin coating was 100°C. The obtained thin film is referred to as "thin film 3."

(Thin film 12)
A dispersion containing nanoparticles 12 (hereinafter referred to as "dispersion 12") was prepared by diluting nanoparticles 12 with an ethanol solvent. The concentration of nanoparticles 12 was 3 wt%. A thin film was formed on an ITO substrate using dispersion liquid 12. The baking treatment temperature after spin coating was 100°C. The obtained thin film is referred to as "thin film 12."

(Thin film 13)
A thin film was formed on a substrate using a dispersion containing nanoparticles 13.

The dispersion liquid was prepared as follows.

Nanoparticles 13 were added to 1-propanol solvent at room temperature and mixed thoroughly. The concentration of nanoparticles 13 was 3 wt%. As a result, a dispersion liquid (hereinafter referred to as "dispersion liquid 13") was prepared.

Next, Dispersion 1 was applied to each of the two types of substrates by a spin coating method to form a coating film. Thereafter, the coating film was baked at 100°C to form a thin film (hereinafter referred to as "thin film 13"). The thickness of the thin film 13 was targeted to be 130 nm.

A silica glass substrate and an ITO substrate were used as the substrates. The thin film 13 on the silica glass substrate was used for flatness evaluation shown below, and the thin film 13 on the ITO substrate was used for work function evaluation.

Table 3 below summarizes the deposition conditions for each thin film.

The following evaluations were performed using each of the obtained dispersions and thin films.

(band gap)
Band gaps were measured for Dispersions 1 to 3.

To measure the band gap, an ultraviolet-visible spectrophotometer (manufactured by JASCO Corporation, product number: V-750) was used, and the value was determined from the obtained light transmission spectrum.

The measurement results revealed that the band gaps of nanoparticles 1 to 3 were 3.42 eV, 3.58 eV, and 3.51 eV, respectively.

(Ionization potential and work function)
Ionization potential and work function were measured using each thin film.

Ultraviolet photoelectron spectroscopy was used to measure the work function. The excitation light used for ultraviolet photoelectron spectroscopy was HeI (21.2 eV).

The measurement results revealed that the ionization potentials of nanoparticles 1 to 3 were 7.0 eV, 6.8 eV, and 6.7 eV, respectively.

It was also found that the work functions of nanoparticles 1 to 3 were 3.7 eV, 3.2 eV, and 3.6 eV, respectively. On the other hand, the work functions of nanoparticles 12 and 13 were found to be 4.0 eV and 3.3 eV, respectively.

(electron affinity)
The electron affinities of nanoparticles 1 to 3 were determined by subtracting the above band gap value from the above ionization potential value. As a result, it was found that the electron affinities of nanoparticles 1 to 3 were 3.6 eV, 2.7 eV, and 3.2 eV, respectively.

(Surface roughness RMS)
The surface roughness (RMS) of thin film 1 and thin film 13 was measured using AFM (Dimension Icon, manufactured by Bruker).

As a result of the measurement, it was found that the surface roughness RMS of thin film 1 was 1.4 nm, and a flat surface was obtained. On the other hand, the surface roughness RMS of thin film 13 was 8 nm, indicating that a flat surface was not obtained.

Table 4 below summarizes the results obtained for each thin film.

In this way, it was confirmed that when a dispersion containing nanoparticles 1 to 3 was used, a thin film with a small work function was formed, and the surface roughness RMS of the obtained thin film was significantly suppressed. .

This application claims priority based on Japanese Patent Application No. 2022-090500 filed on June 2, 2022 and Japanese Patent Application No. 2022-197063 filed on December 9, 2022. The entire content of the same Japanese application is incorporated by reference into this application.

100 OLED
110 Substrate 120 Bottom electrode 130 Hole injection layer/Hole transport layer 140 Organic light emitting layer 150 Additional layer 160 Top electrode 170 Insulating layer 200 QD display 210 Substrate 220 Bottom electrode 230 Hole injection layer/Hole transport layer 240 QD light emitting layer 250 Additional layer 260 upper electrode

Claims (12)

1. Nanoparticles containing a metal oxide,
   In the spectrum of the nanoparticles measured by infrared spectroscopy, the maximum intensity in the region of 400 cm ^-1 to 600 cm ^-1 derived from Zn-O-Zn bonds is defined as I ₁ , and the maximum intensity derived from Zn-O-Si bonds is defined as I 1. When the maximum intensity in the region of 870 cm ^-1 to 970 cm ^-1 is I ₂ and the maximum intensity in the region of 1050 cm ^-1 to 1150 cm ^-1 derived from Si-O-Si bonds is I ₃ , the peak intensity ratio I ₂ /(I ₁ +I ₂ +I ₃ ) is 0.28 or more,
   The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
   The nanoparticles have a Scherrer diameter in the range of 1 nm to 10 nm.
2. Nanoparticles containing a metal oxide,
   The average coordination number of the O atom closest to the Zn atom, determined by X-ray absorption fine structure (XAFS) analysis, is in the range of 3.0 to 4.5, and the X-ray absorption fine structure (XAFS) ) The average coordination number of the Zn atom closest to the Zn atom determined by analysis is in the range of 1.5 to 10,
   The atomic ratio Zn/(Zn+Si) in the nanoparticles is in the range of 0.3 to 0.95,
   The nanoparticles have a Scherrer diameter in the range of 1 nm to 10 nm.
3. The nanoparticle according to claim 1 or 2, wherein the nanoparticle has a work function of 3.9 eV or less.
4. A dispersion liquid comprising the nanoparticles according to claim 1 or 2, a solvent, and a dispersant.
5. An ink comprising the nanoparticles according to claim 1 or 2, a solvent, a dispersant, a thickener, and a surfactant.
6. A thin film comprising the nanoparticles according to claim 1 or 2.
7. comprising a first electrode, an organic light emitting layer, and a second electrode,
   An organic light-emitting diode, comprising an additional layer between the first electrode or the second electrode and the organic light-emitting layer, comprising a thin film according to claim 6.
8. The organic light emitting diode according to claim 7, wherein the additional layer has a surface roughness RMS (root mean square height) of 5 nm or less.
9. It has a first electrode, a quantum dot light emitting layer, and a second electrode,
   A quantum dot display comprising an additional layer comprising the thin film of claim 6 between the first electrode or the second electrode and the quantum dot light emitting layer.
10. The quantum dot display according to claim 9, wherein the surface roughness RMS (root mean square height) of the additional layer is 5 nm or less.
11. A method for producing nanoparticles containing metal oxides, the method comprising:
    (1) mixing raw materials containing zinc and silicon with a first solvent to prepare a first solution;
    (2) preparing a second solution containing an alkali;
    (3) mixing the first solution and the second solution using a flow reactor method to generate a third solution containing nanoparticles;
    (4) adding an additive that suppresses the growth of the nanoparticles to the third solution;
    A method having.
12. 12. The method of claim 11, wherein the additive that inhibits nanoparticle growth is ethyl acetate.

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