JP2020035654A - Light emitting device and method for manufacturing light emitting material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light emitting element and a display device having high quantum efficiency and realizing a wide color gamut, and a method for manufacturing a light emitting material having high quantum efficiency and capable of realizing a wide color gamut. SOLUTION: A light emitting material is produced by using a light emitting material made of an inorganic halide in a light emitting layer of a light emitting element, adding a poor solvent to a precursor substance of the light emitting material, mixing by stirring, and drying under reduced pressure. By doing so, the above problem is solved. [Selection diagram] FIG. 7

Description

  The present invention relates to a light-emitting element in which a light-emitting material of a light-emitting layer is made of an inorganic halide, and a method for manufacturing a light-emitting material.

  An organic EL display device has elements expected from a display device such as a high definition, a high response speed, a high contrast, a wide viewing angle, and a thin type, and is a next-generation display device following a liquid crystal display device and a plasma panel display device. It is attracting attention. 2. Description of the Related Art An organic EL panel used in an organic EL display device is an electrode in which a light-emitting element (organic EL element) using electroluminescence, which emits light when an electric current is applied to an organic material, is arranged on a substrate such as a glass plate and arranged in a grid. An image can be displayed by controlling the light emitting element by (wiring).

As a light emitting material of a light emitting layer of a conventional organic EL, tris (8-hydroxyquinoline) aluminum (Alq ₃ ), tris (2-phenylpyridinato) iridium (III) (Ir (ppy) ₃ ) or the like is used. Have been. However, light-emitting elements using these light-emitting materials are not so high in quantum efficiency and cannot realize a wide color gamut.

Li Na Quan, Rafael Quintero-Bermudez, Oleksandr Voznyy, Grant Walters, Ankit Jain, James Zhangming Fan, Xueli Zheng, Zhenyu Yang, and Edward H. Sargent, Advanced Materials, 29 (21), 1605945 (2017). Satyajit Gupta, Tatyana Bendikov, Gary Hodes, and David Cahen, ACS Energy Lett., 1 (5), 1028-1033 (2016).

  An object of the present invention is to provide a light-emitting element and a display device having high quantum efficiency and realizing a wide color gamut, and a method for manufacturing a light-emitting material having high quantum efficiency and realizing a wide color gamut. .

  The present inventors have conducted intensive studies and have found that a light-emitting material composed of an inorganic halide is used for a light-emitting layer of a light-emitting element, a poor solvent is added to a precursor substance of the light-emitting material, mixed by stirring, and dried under reduced pressure. It has been found that the above-mentioned problem can be solved by performing the method, and the present invention has been completed.

  As described above, the light emitting device of the present invention is characterized in that the light emitting material of the light emitting layer is made of an inorganic halide.

  The inorganic halide, which is a light emitting material of the light emitting layer of the light emitting device of the present invention, is preferably a crystalline metal halide.

The inorganic halide is a luminescent material emitting layer has a light-emitting device of the present invention is preferably a metal halide of the formula A _m B _n X _p.
(Where A is a cation selected from the group consisting of Cs ⁺ , Rb ⁺ , K ⁺ , Na ⁺ , Li ⁺ , and B is selected from the group consisting of Pb ²⁺ , Sn ²⁺ , Ge ²⁺ X is a cation, and X is an anion selected from the group consisting of Cl ⁻ , Br ⁻ , and I ^−. M and n are positive integers, and p is an integer of 3 or more.)
Note that m, n, and p can be written as fractions or decimal numbers, but they are read as integers. In general, the elemental composition of the metal halide may not be strictly an integer due to variation in the composition and the like, but the metal halide of the present invention allows such variation and error.

Further, the inorganic halide which is a light emitting material of the light emitting layer of the light emitting element of the present invention is preferably a metal halide represented by the formula A ₁ B ₁ X ₃ or the formula A ₄ B ₁ X ₆ .

  As described above, the method for producing a light-emitting material of the present invention is characterized in that a poor solvent is added to a precursor substance of a light-emitting material, mixed by stirring, and dried under reduced pressure. In particular, it is preferable to use a ketone-based organic solvent as the poor solvent since separation and purification in the subsequent step are facilitated. Further, it is preferable to dry under reduced pressure at a temperature not higher than the boiling point of the poor solvent.

  In the method for producing a light emitting material of the present invention, the light emitting material is preferably an inorganic halide.

  Further, in the method for producing a light emitting material of the present invention, it is more preferable that the light emitting material is a crystalline metal halide.

In the method of manufacturing the light emitting material of the present invention, it is preferable that the light emitting material is a metal halide of the formula A _m B _n X _p (the symbols in the formula are as defined above).

Furthermore, in the method for producing a luminescent material of the present invention, the luminescent material is preferably a metal halide represented by the formula A ₁ B ₁ X ₃ or the formula A ₄ B ₁ X ₆ .

  In the method for producing a luminescent material according to the present invention, the ketone organic solvent is preferably acetone.

  According to the present invention, it is possible to provide a light emitting element and a display device having high quantum efficiency and realizing a wide color gamut, and a method for manufacturing a light emitting material having high quantum efficiency and realizing a wide color gamut. .

FIG. 3 is a diagram illustrating one embodiment of a light-emitting element of the present invention. In the drawings, “blue”, “green”, and “red” indicate light-emitting materials that emit light of each color. FIG. 3 is a diagram illustrating one embodiment of a light-emitting element of the present invention. It is a figure showing one mode of the manufacturing method of the luminescent material of the present invention. It is a figure showing one mode of the manufacturing method of the luminescent material of the present invention. FIG. 4 is a diagram showing a photoluminescence (Photoluminescence) (PL) spectrum of the light emitting material obtained in Example 1. FIG. 3 is a view showing a scanning electron micrograph of the light emitting material obtained in Example 1. FIG. 9 is a diagram showing a photoluminescence spectrum of the light emitting material obtained in Example 2. FIG. 9 is a view showing an electroluminescence spectrum of the light emitting device obtained in Example 3. It is a figure showing one mode of a display of the present invention. The counter electrode is omitted in the figure.

  Hereinafter, embodiments for carrying out the present invention will be described in detail. The present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within a range that does not impair the effects of the present invention.

[Light-emitting element]
FIG. 1 is a diagram illustrating one embodiment of a light-emitting element of the present invention. In this embodiment, in order from the top, a sealing material (Encapsulant), a cathode (Cathode), an electron transport layer (Electron Transport Layer, ETL), a light emitting layer (Emisive Layer, EML), a hole transport layer (Hole Transport Layer, TH). ), An anode (Anode) and a substrate (Substrate) constitute a light emitting element. There may be an electron injection layer (Electron Injection Layer, EIL) between the cathode and the electron transport layer, and there is a hole injection layer (Hole Injection Layer, HIL) between the hole transport layer and the anode. Is also good. And it may have other several layers.

  When a high potential is applied to the anode and a low potential is applied to the cathode, holes and electrons move to the light-emitting layer via the hole-transport layer and the electron-transport layer, respectively, and combine with each other in the light-emitting layer to emit light. I do. The electron transport layer is formed of an organic substance having an electron transport ability, an organic host substance having an electron transport ability, a compound including an alkali metal such as Li, Na, K, or Cs and an alkali metal, or Mg, Sr, Ba, Alternatively, the organic layer may be an organic layer doped with an alkaline earth metal such as Ra and a compound composed of an alkaline earth metal, but is not limited thereto. The hole transport layer may be an organic material having a hole transport ability or an organic layer in which a dopant is doped into an organic host material having a hole transport ability. In the present invention, the alkaline earth metal refers to a Group 2 element including beryllium and magnesium.

The electron injection layer can be formed from, for example, an inorganic material such as LiF or Li ₂ O, or an alkali metal or alkaline earth metal such as Li, Na, Ca, Mg, Sr, or Ba. The hole injection layer has a hole injection material as a host and may include a p-type dopant.
Further, the electron injection layer of the light emitting element of the present invention is more preferably a metal sodium film made of a material in which metal sodium is dissolved in an organic solvent. Examples of the organic solvent that dissolves metallic sodium include N, N′-dimethylethylene urea, N, N-dimethylacetamide, and N, N′-dimethylpropylene urea.

Examples of electrode materials include metals such as Ag, Al, Mg, and Ca, alloys such as Mg-Ag, indium tin oxide (Indium Tin Oxide, ITO), IZO (In ₂ O ₃ —ZnO), and FTO (fluorine-doped). Oxides such as tin oxide). Generally, a transparent metal oxide is used for the anode and a metal is used for the cathode, but the reverse may be used, and the transparent metal oxide may be used for the cathode and the metal may be used for the anode.

  Metals with a low work function, such as Mg and Ca, also have an effect as an EIL. On the other hand, metals such as Mg and Ca have low mechanical strength, and are generally reinforced with Al or the like.

  Further, Al and Ag also serve as the reflection layer. The light extraction direction is generally designed on the side opposite to the reflective layer, but may be on either the cathode side or the anode side.

  When producing a transparent organic light emitting diode (transparent OLED), an Mg-Ag film, a thin Ag film, or the like is used. There may be ITO or the like under the Ag film, or a structure in which the Ag film is sandwiched between the ITO films from above and below.

  Further, the film made of the above-mentioned material is generally produced by vacuum film formation, but it is also possible to form the film from ink that has been made finer to nano size and dispersed in a solvent. In particular, most of metal halides can be formed into a film from an ink obtained by dissolving a raw material in a solvent. By using ink, various application methods can be applied. Specific examples of the coating method include a spin coating method, an inkjet method, an electrostatic coating method, a method using ultrasonic atomization, a slit coating method, a die coating method, and a screen printing method.

In the light emitting layer of the light emitting device of the present invention, an inorganic halide is used as a light emitting material. The inorganic halide is preferably a crystalline metal halide. The crystalline metal halide, preferably a metal halide of the formula A _m B _n X _p (symbols in the formula are the same as defined above). The metal halide of the formula _A m _B n _{X p,} and more preferably a metal halide represented by the formula _A 1 _B 1 _{X 3} or formula _A 4 _B 1 _{X 6.}
FIG. 2 is a diagram illustrating one embodiment of a light-emitting element of the present invention. The color conversion layer converts blue light emission into green or red light, thereby enabling color reproduction. Although a form using a blue light emitter is shown in the figure, a combination of a blue light emitter and an optical shutter may be used. Further, an up-conversion using a principle such as two-photon absorption may be used.
The light-emitting element of the present invention can realize a display device having high quantum efficiency and realizing a wide color gamut. In addition, it can be manufactured by various vacuum film forming methods and coating methods, and the thickness of the element is thin, so that a large-area flexible display device can be manufactured. In addition, the display device of the present invention also has the features of an organic EL display such as high definition, high response speed, high contrast, wide viewing angle, and thinness.

[Production method of light emitting material]
FIG. 3 is a view showing one embodiment of a method for producing a precursor substance of a luminescent material in the method for producing a luminescent material of the present invention. In this manner, by dissolving PbBr ₂ in dimethyl sulfoxide, the CsBr was dissolved in water, while cooling the PbBr ₂ dissolved in dimethyl sulfoxide is stirred by mixing CsBr dissolved in water, the light-emitting material Is obtained.

In this case, the molar ratio (Cs / Pb) of CsBr and PbBr ₂ is preferably 6 or more. Further, the cooling temperature is preferably 50 ° C. or lower, more preferably 30 ° C. or lower.

  In addition, a poor solvent, for example, acetone is added to this precursor substance, mixed by stirring, and dried under reduced pressure at room temperature, whereby a luminescent powder having a high quantum yield, which is a luminescent material, can be produced. It is. In the step of drying under reduced pressure, the temperature is preferably 50 ° C. or lower, more preferably 30 ° C. or lower.

FIG. 4 is also a view showing one embodiment of a method for producing a precursor substance of a luminescent material in the method for producing a luminescent material of the present invention. In this embodiment, SnBr ₂ is dissolved in dimethyl sulfoxide, CsBr is added, a Na dispersion is added, and the mixture is stirred while heating to obtain a precursor substance of a light emitting material.

  In this case, the heating temperature is preferably from 50 ° C to 100 ° C.

  In addition, a poor solvent, for example, acetone is added to this precursor substance, mixed by stirring, and dried under reduced pressure, whereby a luminescent material powder having a high quantum yield, which is a luminescent material, can be produced. In the step of drying under reduced pressure, the temperature is preferably 50 ° C. or lower, more preferably 30 ° C. or lower.

As the light emitting material produced by the method for producing a light emitting material of the present invention, an inorganic halide is preferred. The inorganic halide is preferably a crystalline metal halide. The crystalline metal halide, preferably a metal halide of the formula A _m B _n X _p (symbols in the formula are the same as defined above). The metal halide of the formula _A m _B n _{X p,} is preferably a metal halide represented by the formula _A 1 _B 1 _{X 3} or formula _A 4 _B 1 _{X 6.} In addition, the poor solvent used in the method for producing a light emitting material of the present invention is preferably a ketone organic solvent, and more preferably acetone.
The light emitting material of the present invention can be used for the above light emitting device of the present invention. As an excitation source for light emission, direct injection of electric charge or excitation by light can be used.
The metal halide of the present invention has high quantum efficiency and can realize a wide color gamut. Although the principle is not clear, the metal halide of the present invention is a highly ionic semiconductor, easily has a specific crystal structure, and is unlikely to have an impurity level in a band gap, so that high quantum efficiency and full width at half maximum are obtained. Can be presumed to provide light emission having a narrow characteristic.

  Although the preferred embodiments of the present invention have been described in detail, various modifications and equivalent embodiments are possible from those skilled in the art.

  Therefore, the scope of the present invention is not limited to this, and various modifications and improvements of those skilled in the art using the basic concept of the present invention defined in the claims are also included in the present invention.

  Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited to these Examples.

[Example 1]
(Synthesis of high quantum yield phosphor powder, Cs-Pb-Br compound)
The PbBr ₂ of 0.028g were dissolved in dimethyl sulfoxide 2.0 ml (DMSO). Then, 0.128 g of CsBr was dissolved in 0.6 ml of water. While cooling PbBr ₂ dissolved in DMSO at 25 ° C., mixing and stirring CsBr dissolved in water, 6.0 ml of acetone was added and mixed by stirring. By drying under reduced pressure at 25 ° C., a Cs—Pb—Br compound, which is a phosphor powder, was obtained.

[Comparative Example 1]
Except that the step of mixing CsBr dissolved in water with PbBr ₂ dissolved in DMSO was performed at 50 ° C. or higher, a Cs-Pb-Br compound as a luminous powder was prepared in the same manner as in Example 1. Obtained.

[Comparative Example 2]
A Cs-Pb-Br compound as a phosphor powder was obtained in the same manner as in Example 1, except that the step of drying under reduced pressure was performed at 70 ° C.

  Table 1 shows the photoluminescence quantum efficiencies of the Cs-Pb-Br compound powders obtained in Example 1 and Comparative Examples 1 and 2.

  As shown in Table 1, the Cs—Pb—Br compound powder obtained in Example 1 has a very high photoluminescence quantum efficiency of 96%. On the other hand, the photoluminescence quantum efficiencies of the Cs—Pb—Br compound powders obtained in Comparative Examples 1 and 2 are both less than 80%.

  FIG. 5 shows a photoluminescence spectrum of the Cs—Pb—Br compound powder obtained in Example 1. At room temperature, a photoluminescence spectrum having a peak at a center wavelength of 523 nm at an excitation wavelength of 400 nm was obtained. Further, the full width half maximum (FWHM) was 24 nm.

  Further, a scanning electron micrograph of the Cs-Pb-Br compound powder obtained in Example 1 is shown in FIG. As shown in FIG. 6, a uniform powder having an average particle size of about 10 μm is obtained.

[Example 2]
(Synthesis of high quantum yield phosphor powder, Cs-Sn-Br compound)
0.222 g of SnBr ₂ was dissolved in 1.0 ml of DMSO. Then, 0.170 g of CsBr was added. 4 μl of a Na dispersion (Shinko Environmental Solutions Co., Ltd., sodium dispersion SD) was added, stirred while heating at 80 ° C., 6.0 ml of acetone was added, and mixed by stirring. Drying under reduced pressure at normal temperature gave a Cs-Sn-Br compound, which was a phosphor powder.

[Comparative Example 3]
A Cs-Sn-Br compound as a phosphor powder was obtained in the same manner as in Example 2, except that the step of adding the Na dispersion was not performed.

  Table 2 shows the photoluminescence quantum efficiencies of the Cs—Sn—Br compound powders obtained in Example 2 and Comparative Example 3.

  As shown in Table 2, the Cs—Sn—Br compound powder obtained in Example 2 exhibited a photoluminescence quantum efficiency of 22%. On the other hand, the photoluminescence quantum efficiency of the Cs—Sn—Br compound powder obtained in Comparative Example 3 was 5%.

  FIG. 7 shows a photoluminescence spectrum of the Cs—Sn—Br compound powder obtained in Example 2. A photoluminescence spectrum having a peak at a center wavelength of 589 nm at an excitation wavelength of 400 nm was obtained. The full width at half maximum was 173 nm.

[Example 3]
(Production of light emitting element)
A light emitting element having the following configuration was manufactured.
ITO / NPD / Cs-Pb-Br compound / Bphen / LiF / Al
(Anode / HTL / EML / ETL / EIL / cathode)
NPD represents N, N'-di-1-naphthyl-N, N'-diphenylbenzidine, Bphen represents batophenanthroline, and LiF represents lithium fluoride. When a voltage was applied to both electrodes, the electroluminescence emission spectrum shown in FIG. 8 was confirmed. The center wavelength of the emission peak is 519 nm, and the full width at half maximum is 28 nm.

Claims (18)

  A light-emitting element, wherein the light-emitting material of the light-emitting layer comprises an inorganic halide.   The light emitting device according to claim 1, wherein the inorganic halide is a crystalline metal halide. Crystalline metal halide is a metal halide of the formula A _m B _n X _p, the light-emitting device according to claim 2.
(Where A is a cation selected from the group consisting of Cs ⁺ , Rb ⁺ , K ⁺ , Na ⁺ , and Li ⁺ , and B is a cation selected from the group consisting of Pb ²⁺ , Sn ²⁺ , and Ge ^2+. X is an anion selected from the group consisting of Cl ⁻ , Br ⁻ , and I ^−. M and n are positive integers, and p is an integer of 3 or more.) Crystalline metal halide is a metal halide of the formula _A 1 _B 1 _{X 3} or formula _A 4 _B 1 _{X 6,} light emitting device according to claim 3.   The light emitting device according to claim 4, wherein the crystalline metal halide is a metal halide containing Cs and Pb or a metal halide containing Cs and Sn.   A display device comprising the light-emitting element according to claim 1.   A method for producing a luminescent material, comprising adding a poor solvent to a precursor substance of a luminescent material, mixing by stirring, and drying under reduced pressure.   The method for producing a luminescent material according to claim 7, wherein the luminescent material is an inorganic halide.   The method for producing a luminescent material according to claim 8, wherein the inorganic halide is a crystalline metal halide. Crystalline metal halide is a metal halide of the formula A _m B _n X _p, the method of manufacturing the light emitting material according to claim 9.
(Where A is a cation selected from the group consisting of Cs ⁺ , Rb ⁺ , K ⁺ , Na ⁺ , and Li ⁺ , and B is a cation selected from the group consisting of Pb ²⁺ , Sn ²⁺ , and Ge ^2+. X is an anion selected from the group consisting of Cl ⁻ , Br ⁻ , and I ^−. M and n are positive integers, and p is an integer of 3 or more.) Crystalline metal halide is a metal halide of the formula _A 1 _B 1 _{X 3} or formula _A 4 _B 1 _{X 6,} a manufacturing method of a light-emitting material according to claim 10.   The method according to claim 11, wherein the crystalline metal halide is a metal halide containing Cs and Pb or a metal halide containing Cs and Sn.   The method for producing a luminescent material according to any one of claims 7 to 12, wherein the poor solvent is acetone. 8. The method according to claim ₇ , wherein PbBr ₂ is dissolved in dimethyl sulfoxide, CsBr is dissolved in water, and CsBr dissolved in water is mixed and stirred while cooling PbBr ₂ dissolved in dimethyl sulfoxide. 14. The method for producing a precursor substance for a light-emitting material according to any one of items 13 to 13.   The method for producing a precursor substance of a luminescent material according to claim 14, wherein the cooling temperature is 50 ° C or less. The method for producing a precursor substance of a luminescent material according to any one of claims 7 to 13, wherein SnBr ₂ is dissolved in dimethyl sulfoxide, CsBr is added, and the mixture is stirred while being heated.   The method for producing a precursor substance for a luminescent material according to claim 16, wherein the heating temperature is 50C or higher and 100C or lower.   A display device comprising the luminescent material according to claim 7.