KR20250016861A - Lead-free metal halide nanoparticle, preparation method thereof and emitting device comprising the same as emitting layer - Google Patents

Abstract

The present invention relates to a lead-free metal halide nanoparticle, a method for producing the same, and a light-emitting device comprising the same as a light-emitting layer. The metal halide comprises a compound represented by the following chemical formula 1, has an orthorhombic crystal structure, has a space group of Pnma, and has a particle size of 10 nm or more and less than 20 nm.
[Chemical Formula 1]
A ₂ Mn(X ¹ _1-a X ² _a ) ₄
(In the chemical formula 1 above, A is an alkali metal element, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.0.)
According to the present invention, a bulk-type lead-free metal halide is nano-sized into a smaller size, thereby reducing the half-width from 30 to 40 nm in the bulk form to 20 to 25 nm, thereby improving color purity when used as a light-emitting layer of a light-emitting device.

Description

Lead-free metal halide nanoparticle, preparation method thereof and emitting device comprising the same as emitting layer

The present invention relates to metal halides, and more particularly, to non-lead metal halides.

The light-emitting device industry, such as liquid crystal display (LCD) display, is looking for solutions to improve the efficiency of LCD and enhance their color gamut (color content of the display) to compete with organic light-emitting diode display (OLED) products. Conventional LCDs lag behind OLEDs, especially in color gamut performance. The use of quantum dots (QD) in LCD has improved the color gamut performance of LCD.

Recently, perovskite materials, which have been in the spotlight, have various band gaps and color control according to them by controlling halogen elements, high photoluminescence quantum yield (PLQY), and narrow full width at half maximum (FWHM) of ~20 nm. It is known that this can be applied to the color filter of LCD to realize high color purity and high color reproducibility LCD.

However, high-performance perovskites contain lead (Pb) as a metal cation. In the European Union, the use of hazardous heavy metals including lead in electronic devices is regulated by the Restriction of Hazardous Substances Directive (RoHS), and other countries are expected to gradually introduce such regulations.

Accordingly, there is a demand for the manufacture of light-emitting elements that include non-lead light-emitting bodies but have improved color purity.

Republic of Korea Publication Patent No. 10-2001-0015084 (2001.02.26.)

The problem to be solved by the present invention is to provide green luminescent lead-free metal halide nanoparticles with improved color purity.

In addition, another problem to be solved by the present invention is to provide a method for producing the green luminescent non-lead metal halide nanoparticles.

Furthermore, another problem to be solved by the present invention is to provide a light-emitting device including the green light-emitting non-lead metal halide nanoparticles as a light-emitting layer.

In order to achieve the above technical task, one aspect of the present invention provides a lead-free metal halide nanoparticle. The lead-free metal halide nanoparticle is characterized in that it includes a compound represented by the following chemical formula 1, has an orthorhombic crystal structure, has a space group of Pnma, and has a particle size of 10 nm or more and less than 20 nm.

[Chemical Formula 1]

A ₂ Mn(X ¹ _1-a X ² _a ) ₄

In the chemical formula 1, A is an alkali metal element, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.0.

The compound represented by the above chemical formula 1 may be a compound represented by the following chemical formula 2:

[Chemical formula 2]

Cs ₂ Mn(X ¹ _1-a X ² _a ) ₄

In the above chemical formula 2, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.

Specifically, in the chemical formula 2, a can be one of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0.

The above compound is characterized by emitting light in the green region through the d orbital level of Mn ²⁺ when irradiated with incident light in the ultraviolet to blue region or when voltage is applied.

In addition, another aspect of the present invention provides a method for producing the green light-emitting lead-free metal halide nanoparticles. The method for producing the green light-emitting lead-free metal halide nanoparticles includes the steps of producing a bulk metal halide of chemical formula 1; putting the bulk metal halide of chemical formula 1 into a nonpolar solvent and dispersing it using ultrasonic waves to produce an ultrasonic dispersion; and centrifuging the ultrasonic dispersion and then taking the supernatant to produce the metal halide nanoparticles of chemical formula 1.

The step of manufacturing the metal halide of the chemical formula 1 in bulk includes the step of mixing raw materials AX ¹ , AX ² , MnX ¹ ₂ , and MnX ² ₂ in a stoichiometric equivalent ratio to obtain a mixture; and the step of calcining the mixture in an inert gas atmosphere or a reducing atmosphere and then naturally cooling to obtain the metal halide of the chemical formula 1 in bulk.

The step of preparing the above ultrasonic dispersion may further include a polar solvent in the nonpolar solvent.

The step of preparing the above ultrasonic dispersion may further include an acid or base additive in the nonpolar solvent to adjust pH.

The above nonpolar solvent may be an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon-based organic solvent.

In addition, another aspect of the present invention provides a light-emitting device comprising the non-lead metal halide nanoparticles as a light-emitting layer.

The above light-emitting element may be a photoluminescent element.

The above light-emitting element may be an electroluminescent element including a positive electrode and a negative electrode, and a light-emitting layer disposed between the positive electrode and the negative electrode.

The light-emitting element may further include at least one layer of a hole injection layer, a hole transport layer, and an electron blocking layer disposed between the positive electrode and the light-emitting layer, and at least one layer of an electron injection layer, an electron transport layer, and a hole blocking layer disposed between the light-emitting layer and the negative electrode.

The above light-emitting element may have an emission wavelength of 500 nm to 550 nm when irradiated with incident light in the ultraviolet to blue range or when voltage is applied.

The half-width of the emission peak of the above light-emitting element is characterized by being 20 to 25 nm.

According to the present invention, a bulk non-lead metal halide is nano-sized into a smaller size, thereby reducing the half-width from 30 to 40 nm in the bulk form to 20 to 25 nm, thereby improving color purity and enabling it to be usefully used as a light-emitting layer of a light-emitting device.

The effects of the present invention are not limited to those mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art from the description below.

Figure 1 shows the crystal structure of a non-lead metal halide compound according to one embodiment of the present invention.
FIG. 2 shows X-ray diffraction analysis of bulk-type lead-free metal halide particles and lead-free metal halide nanoparticles according to one comparative example and one embodiment of the present invention.
FIG. 3 is a transmission electron microscope (TEM) image showing the size of non-lead metal halide nanoparticles according to one embodiment of the present invention.
Figure 4 is a flow chart showing a method for manufacturing non-lead metal halide nanoparticles according to one embodiment of the present invention.
FIG. 5 is a flow chart showing the manufacturing steps of bulk-type lead-free metal halide particles according to one embodiment of the present invention.
FIG. 6 is a drawing showing a cross-section of a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.
FIG. 7 shows an energy level diagram of a light-emitting device including lead-free metal halide nanoparticles as a light-emitting layer according to one embodiment of the present invention.
FIG. 8 is a diagram comparing the photoluminescence and photoexcitation spectra of bulk-type lead-free metal halide particles and lead-free metal halide nanoparticles according to one comparative example and one embodiment of the present invention.
FIG. 9 shows an electroluminescence spectrum according to an applied voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.
FIG. 10 is a graph showing the time-resolved photoluminescence results of non-lead metal halide nanoparticles according to one embodiment of the present invention.
FIG. 11 is a graph showing the electroluminescence brightness according to the driving voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.
FIG. 12 is a graph showing current density according to driving voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.

Hereinafter, in order to explain the present invention more specifically, preferred embodiments according to the present invention will be described in more detail with reference to the attached drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms.

Throughout this specification, whenever a part is said to "include" a component, this does not mean that it excludes other components, but rather that it may include other components, unless otherwise specifically stated.

The terms “about,” “substantially,” and the like, as used throughout this specification, are used to mean at or near the numerical value when a material tolerance is presented in the sense stated, and are used to prevent unscrupulous infringers from unfairly exploiting the disclosure, which states precise or absolute numerical values to aid understanding of the present application.

When an element such as a layer, region or substrate is referred to as existing "on" another element, it will be understood that this may either be directly on the other element or there may be intermediate elements between them.

Although the terms first, second, etc. may be used to describe various elements, components, regions, layers and/or regions, it will be understood that these elements, components, regions, layers and/or regions should not be limited by these terms.

In this specification, “light-emitting element” may include any element that emits light, such as a light-emitting diode, a light-emitting transistor, a laser, or a polarized light-emitting element.

In this specification, “bulk” means a state in which nanocrystal particles are aggregated to form polycrystals and have an irregularly shaped particle size of several hundred nm.

[Lead-free metal halide nanoparticles]

One aspect of the present invention provides lead-free metal halide nanoparticles.

The non-lead metal halide nanoparticles according to the present invention are characterized in that they include a compound represented by the following chemical formula 1, have an orthorhombic crystal structure, and have a particle size of 10 nm or more and less than 20 nm.

[Chemical Formula 1]

A ₂ Mn(X ¹ _1-a X ² _a ) ₄

In the above chemical formula 1, A may be at least one element among alkali metal elements, specifically Li, Na, K, Rb, and Cs.

As different halogen elements of X ¹ and X ² , for example, X ¹ can be Br and X ² can be Cl or F.

a is between 0 and 1.0. Specifically, a can be one of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0.

The above A may be a monovalent cation, Mn may be a divalent cation, and X ¹ and X ² may be monovalent anions. This compound is a metal halide containing Mn as a divalent metal, and may not be harmful to the environment because it does not contain lead.

The compound represented by the above chemical formula 1 may be a compound represented by the following chemical formula 2:

[Chemical formula 2]

Cs ₂ Mn(X ¹ _1-a X ² _a ) ₄

In the above chemical formula 2, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.

The compound of the above chemical formula 2 is a compound in which A of the chemical formula 1 is Cs.

Specifically, in the chemical formula 2, a can be one of 0, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0.

Figure 1 shows the crystal structure of a non-lead metal halide compound represented by Chemical Formula 1 or Chemical Formula 2 according to one embodiment of the present invention.

Referring to FIG. 1, the compound represented by the chemical formula 1 or 2 has an orthorhombic crystal structure and may have a space group of Pnma. Specifically, it may have MnX ₄ tetrahedra with Mn ²⁺ at the center and four Xs positioned at each vertex, and A ⁺ s positioned between them.

Here, the distance between a pair of Mn ²⁺ ions, which are luminescent centers, is relatively far, about 8 to 12 Å, so that excellent luminescent properties and high thermal stability can be achieved. In particular, when the compound is Cs ₂ MnBr ₄ , the distance between the Mn ²⁺ ions can be 8.2 Å or 11.2 Å.

FIG. 2 shows X-ray diffraction analysis of bulk-type lead-free metal halide particles and lead-free metal halide nanoparticles according to one comparative example and one embodiment of the present invention.

Referring to FIG. 2, the lead-free metal halide compound has the same crystal structure in bulk particles and nanoparticles, and this crystal structure is orthorhombic and the space group is Pnma. In addition, even when a relatively large amount of Br ^- was substituted with Cl ^- , the crystal structure was maintained. This can be seen as a result of the decrease in ion movement because the ionic binding energy of Cl ^- for the crystal frame is increased compared to Br ^- .

FIG. 3 is a transmission electron microscope (TEM) image showing the size of non-lead metal halide nanoparticles according to one embodiment of the present invention.

Referring to Figure 3, it was confirmed that the non-lead metal halide nanoparticles exhibit a particle size of 10 nm or more and less than 20 nm.

The above compound is characterized by emitting light in the green region through the d orbital level of Mn ²⁺ when receiving incident light in the ultraviolet to blue region or when an operating voltage is applied.

Specifically, in the lead-free metal halide nanoparticle represented by the chemical formula 1, Mn ²⁺ has electrons arranged in five 3d orbitals, and when it binds to a ligand, the dz ² and dx ² -y ² orbitals and the dxy, dyz, and dxz orbitals can undergo crystal field splitting, in which energy is separated. In particular, when Mn ²⁺ binds to four ligands to form a tetrahedral structure, the dz ² and dx ² -y ² orbitals form a low energy level (e), and the dxy, dyz, and dxz orbitals form a high energy level (t2).

By this crystal field separation, the lead-free metal halide nanoparticles can have a band gap of about 2.3 to 2.4 eV. Accordingly, the lead-free metal halide nanoparticles can emit light in the green range, specifically about 500 nm to 550 nm, for example, 515 to 525 nm, when light in the ultraviolet to blue range, specifically about 200 to 500 nm, more specifically about 370 to 490 nm, for example, about 450 to 480 nm, is incident (see FIG. 8). In addition, it was shown that green light of about 500 nm to 550 nm was also emitted when an operating voltage was applied (see FIG. 9). Moreover, since the non-lead metal halide nanoparticles exhibit a small half-width of the emission peak, for example, 20 to 25 nm, they can exhibit excellent color purity by reducing the half-width compared to the half-width of existing bulk particles (30 to 45 nm) (see FIGS. 8 and 9).

The lead-free metal halide nanoparticles according to the present invention, unlike conventional quantum dots (QDs) whose surfaces are covered with organic ligands, have a strong bonding force to the surface potential, and thus have high phase stability against the external environment. In addition, since they have a luminescence mechanism through the d orbital level of Mn ²⁺ , they have relatively little crystal phase dependence in terms of luminescence characteristics and can have high luminescence stability, and therefore can be usefully used as a luminescent layer of a light-emitting device.

[Method for producing non-lead metal halide nanoparticles]

In addition, another aspect of the present invention provides a method for producing the non-lead metal halide nanoparticles.

Figure 4 is a flow chart showing a method for manufacturing non-lead metal halide nanoparticles according to one embodiment of the present invention.

Referring to Fig. 4, the method for manufacturing the non-lead metal halide nanoparticles is

A step for producing a metal halide of chemical formula 1 in bulk form;

A step of preparing an ultrasonic dispersion by placing the metal halide of the chemical formula 1 in a nonpolar solvent and dispersing it using ultrasonic waves; and

It includes a step of centrifuging the above ultrasonic dispersion and then taking the supernatant to produce metal halide nanoparticles of chemical formula 1.

Hereinafter, a method for manufacturing non-lead metal halide nanoparticles according to the present invention is described in detail step by step.

First, a bulk metal halide of chemical formula 1 is prepared.

FIG. 5 is a flow chart showing the manufacturing steps of bulk-type lead-free metal halide particles according to one embodiment of the present invention.

Referring to FIG. 5, the step of manufacturing the bulk type metal halide of chemical formula 1 includes the step of mixing raw materials AX ¹ , AX ² , MnX ¹ ₂ , and MnX ² ₂ in a stoichiometric equivalent ratio to obtain a mixture; and the step of calcining the mixture in an inert gas atmosphere or a reducing atmosphere and then naturally cooling to obtain the bulk type metal halide of chemical formula 1.

First, the raw materials AX ¹ , AX ² , MnX ¹ ₂ , and MnX ² ₂ can be mixed in a stoichiometric equivalent ratio, specifically a molar ratio of 2-2a:2a:1-a:a, to obtain a mixture. At this time, X ¹ and X ² may be as defined in the chemical formula 1 above. Specifically, in the case of a compound such as chemical formula 2, the mixture can be obtained by mixing CsX ¹ , CsX ² , MnX ¹ ₂ , and MnX ² ₂ in a stoichiometric equivalent ratio, specifically a molar ratio of 2-2a:2a:1-a:a.

The above mixing process can be performed in an inert gas atmosphere, for example, argon. Specifically, the mixing process can be performed by mixing and grinding the raw materials at the above molar ratio using an agate pestle and a mortar in a glove box filled with argon to obtain a mixture. The mixing can be performed for 15 minutes to 1 hour.

The above mixture can be calcined in an inert gas atmosphere or a reducing atmosphere and then naturally cooled to obtain a bulk compound according to the chemical formula 1 or 2. The inert gas atmosphere can be an argon atmosphere, and the reducing atmosphere can be a hydrogen atmosphere. The calcination can be performed after filling the mixture into an alumina crucible and then placing the crucible filled with the mixture into an alumina tube electric furnace. In addition, the calcination can be performed by increasing the temperature to about 600 to 700°C, specifically, 625 to 675°C, and maintaining the increased temperature for 10 to 26 hours, specifically, 23 to 25 hours after the heating is completed.

The above naturally cooled compound can be pulverized to obtain a bulk metal halide powder of chemical formula 1.

Next, the metal halide of the chemical formula 1 in bulk form is placed in a nonpolar solvent and dispersed using ultrasonic waves to prepare an ultrasonic dispersion.

The nonpolar solvent may be any nonpolar solvent known in the art capable of uniformly dispersing the bulk metal halide, and may be a nonpolar solvent having a dielectric constant of 15 or less, specifically, an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon-based organic solvent. Specifically, the nonpolar solvent may be at least one of hexane, cyclohexane, toluene, chlorobenzene, benzene, chloroform, and diethyl ether, but is not limited thereto.

The solvent may further include a polar solvent in addition to the nonpolar solvent. The polar solvent may be a polar solvent known in the art, and examples thereof include, but are not limited to, water, acetone, ethanol, butanol, isopropanol, and methanol. It is preferable to mix the polar solvent in a volume ratio of 1:9 to 9:1 with respect to the nonpolar solvent, and dispersion of the bulk metal halide may be effectively performed within the above-mentioned range.

In addition, the solvent may further include an acid or base additive for pH control in a nonpolar solvent. Specifically, the solvent may include a weak acid salt substance such as sodium acetate or potassium acetate for pH control to 5 to 6. When the pH is controlled to 5 to 6, dispersion of the bulk metal halide can be effectively performed.

The above ultrasonic dispersion can perform dispersion from bulk particles to nanoparticles by simultaneously causing erosion dispersion of aggregated particles by shock waves using a plurality of piezoelectric vibrators and generating eddies in the solution by ultrasonic streaming to cause fragmentation dispersion by fluid shear force. The above ultrasonic dispersion can be performed at 5 to 20 W, and the treatment time is preferably 10 minutes to 1 hour, but is not limited thereto, and can be performed until all bulk powders are pulverized.

Next, the ultrasonic dispersion is centrifuged and the supernatant is taken to prepare metal halide nanoparticles of chemical formula 1.

Performing a centrifugation process after the above ultrasonic treatment can increase the yield and dispersion stability of the metal halide nanoparticles of chemical formula 1. At this time, the precipitate produced by the centrifugation process is a bulk powder that has not been nano-ized, and by removing the precipitate and taking the supernatant and drying it, the metal halide nanoparticles can be manufactured.

At this time, the centrifugation speed is performed at 4,000 to 12,000 rpm, preferably 8,000 to 9,000 rpm, and the centrifugation time can be performed for 10 to 30 minutes.

The manufactured metal halide nanoparticles may have a particle size of 10 nm or more and less than 20 nm, as shown in Fig. 3.

[Light-emitting element]

In addition, another aspect of the present invention provides a light-emitting device comprising the non-lead metal halide nanoparticles as a light-emitting layer.

As described above, the above-described non-lead metal halide nanoparticles can exhibit photoluminescence (PL) characteristics and electroluminescence (EL) characteristics, and therefore can be used as a light-emitting layer of a photoluminescence device or an electroluminescence device.

FIG. 6 is a drawing showing a cross-section of a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.

Referring to FIG. 6, a light-emitting device according to the present invention may include a positive electrode (20) and a negative electrode (100); a light-emitting layer (60) disposed between these two electrodes; and a hole injection layer (30) for facilitating the injection of holes may be disposed between the positive electrode (20) and the light-emitting layer (60). In addition, an electron transport layer (80) for transporting electrons and an electron injection layer (90) for facilitating the injection of electrons may be disposed between the light-emitting layer (60) and the negative electrode (100). In addition, the light-emitting device according to the present invention may further include a hole transport layer (40) for transporting holes between the hole injection layer (30) and the light-emitting layer (60). In addition, a hole blocking layer (70) may be disposed between the light-emitting layer (60) and the electron transport layer (80). Additionally, an electron blocking layer (50) may be placed between the light-emitting layer (40) and the hole transport layer (40).

The positive electrode (20) may be a conductive metal oxide, a metal, a metal alloy, or a carbon material. The conductive metal oxide may be indium tin oxide (ITO), fluorine tin oxide (FTO), antimony tin oxide (ATO), fluorine doped tin oxide (FTO), SnO ₂ , ZnO, or a combination thereof. Metals or metal alloys suitable as the positive electrode (20) may be Au and CuI. The carbon material may be graphite, graphene, or carbon nanotubes.

The above negative electrode (100) is a conductive film having a lower work function than the positive electrode (20), and can be formed using, for example, a metal such as aluminum, magnesium, calcium, sodium, potassium, indium, yttrium, lithium, silver, lead, cesium, or a combination of two or more of these.

The positive electrode (20) and the negative electrode (100) above can be formed using a sputtering method, a vapor deposition method, or an ion beam deposition method. The hole injection layer (30), the hole transport layer (40), the electron blocking layer (50), the light emitting layer (60), the hole blocking layer (70), the electron transport layer (80), and the electron injection layer (90) can be formed, regardless of each other, using a deposition method or a coating method, for example, spraying, spin coating, dipping, printing, doctor blading, or using an electrophoresis method.

The above hole injection layer (30) and hole transport layer (40) may include materials commonly used as hole transport materials, and one layer may have different hole transport material layers. The hole transport materials include, for example, mCP (N,Ndicarbazolyl-3,5-benzene); PEDOT:PSS (poly(3,4-ethylenedioxythiophene):polystyrenesulfonate); NPD (N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine); TPD (N,N′-Bis(3-methylphenyl)-N,N′-diphenylbenzidine); DNTPD (N ⁴ ,N ^4′ -Bis[4-[bis(3-methylphenyl)amino]phenyl]-N ⁴ ,N ^4′ -diphenyl-[1,1′-biphenyl]-4,4′-diamine); Porphyrin compound derivatives such as N,N'-diphenyl-N,N'-dinaphthyl-4,4'-diaminobiphenyl;N,N,N'N'-tetra-p-tolyl-4,4'-diaminobiphenyl;N,N,N'N'-tetraphenyl-4,4'-diaminobiphenyl;copper(II)1,10,15,20-tetraphenyl-21H,23H-porphyrin; triarylamine derivatives such as TAPC(1,1-Bis[4-[N,N'-Di(p-tolyl)Amino]Phenyl]Cyclohexane); N,N,N-tri(p-tolyl)amine, 4,4', 4'-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine; carbazole derivatives such as N-phenylcarbazole and polyvinylcarbazole; It may be a phthalocyanine derivative such as a metal-free phthalocyanine, copper phthalocyanine; a starburst amine derivative; an enamine stilbene derivative; a derivative of an aromatic tertiary amine and a styryl amine compound; and a polysilane. Such a hole transport material may also function as an electron blocking layer (50).

The thickness of the above hole injection layer (30) may be 10 Å to 10,000 Å, for example, 100 Å to 1,000 Å. When the thickness of the above hole injection layer satisfies the range described above, the driving voltage does not increase, so a high-quality organic device can be implemented.

The thickness of the above hole transport layer (40) may be 5 nm to 100 nm, for example, 10 nm to 60 nm. When the thickness of the above hole transport layer satisfies the range described above, the light efficiency of the organic light emitting diode may be improved and the brightness may be increased.

The electron injection layer (90) and the electron transport layer (80) are layers having a LUMO level between the work function level of the cathode (100) and the LUMO level of the light-emitting layer (60), and function to increase the injection efficiency and transport efficiency of electrons from the cathode (100) to the light-emitting layer (60).

The electron injection layer (90) may be, for example, LiF, NaCl, CsF, Li ₂ O, BaO, BaF ₂ , or Liq (lithium quinolate). In addition, the electron injection layer (90) may include a metal oxide. The metal oxide has an n-type semiconductor characteristic, so it has excellent electron transport ability, and further, it may be selected from among semiconductor materials that are not reactive to air or moisture and have excellent transparency in the visible light range. The electron injection layer (90) may be, for example, aluminum doped zinc oxide (AZO), alkali metal (Li, Na, K, Rb, Cs or Fr) doped AZO, TiO _x (x is a real number from 1 to 3), indium oxide (In ₂ O ₃ ), tin oxide (SnO ₂ ), zinc oxide (ZnO), zinc tin oxide (Zinc Tin Oxide), gallium oxide (Ga ₂ O ₃ ), tungsten oxide (WO ₃ ), aluminum oxide, titanium oxide, vanadium oxide (V ₂ O ₅ , vanadium(IV) oxide(VO ₂ ), V ₄ O ₇ , V ₅ O ₉ , or V ₂ O ₃ ), molybdenum oxide (MoO ₃ or MoO _x ), copper oxide (Copper(II) Oxide: CuO), nickel oxide (NiO), It may include one or more metal oxides selected from among copper aluminum oxide (CAO, CuAlO ₂ ), zinc rhodium oxide (ZRO, ZnRh ₂ O ₄ ), iron oxide, chromium oxide, bismuth oxide, indium-gallium zinc oxide (IGZO), and ZrO ₂ , but is not limited thereto. As an example, the electron injection layer (60) may be a metal oxide thin film layer, a metal oxide nanoparticle layer, or a layer including metal oxide nanoparticles in a metal oxide thin film.

The electron transport layer (80) is a quinoline derivative, particularly tris(8-hydroxyquinoline) aluminum (Alq ₃ ), bis(2-methyl-8-quinolinolate)-4-(phenylphenolato)aluminium (Balq), bis(10-hydroxybenzo [h] quinolinato)-beryllium (Bebq ₂ ), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP), 4,7-diphenyl-1,10-phenanthroline. (4,7-diphenyl-1,10-phenanthroline : Bphen), 2,2',2"-(benzene-1,3,5-triyl)-tris(1-phenyl-1H-benzimidazole) ((2,2',2"-(benzene-1,3,5-triyl)- tris(1-phenyl-1H-benzimidazole : TPBI), 3-(4-biphenyl)-4-(phenyl-5-tert-butylphenyl-1,2,4-triazole (3-(4-biphenyl)-4-phenyl-5-tert-butylphenyl-1,2,4-triazole : TAZ), 4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole (4-(naphthalen-1-yl)-3,5-diphenyl-4H-1,2,4-triazole : NTAZ), 2,9-bis(naphthalen-2-yl)-4,7-diphenyl-1,10-phenanthroline (NBphen), Tris(2,4,6-trimethyl-3-(pyridin-3-yl)phenyl)borane (3TPYMB), Phenyl-dipyrenylphosphine oxide (POPy2), 3,3',5,5'-tetra[(m-pyridyl)-phen-3-yl]biphenyl (BP4mPy), 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB), 1,3-bis[3,5-di(pyridin-3-yl)phenyl]benzene (BmPyPhB), bis(10-hydroxybenzo[h]quinolinato)beryllium (Bepq2), , diphenylbis(4-(pyridin-3-yl)phenyl)silane (DPPS), and 1,3,5-tri(p-pyrid-3-yl-phenyl)benzene (1,3,5-tri(p-pyrid-3-yl-phenyl)benzene : TpPyPB), 1,3-bis[2-(2,2'-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene (1,3-bis[2-(2,2'-bipyridine-6-yl)-1,3,4-oxadiazo-5-yl]benzene : Bpy-OXD), 6,6'-bis[5-(biphenyl-4-yl)-1,3,4-oxadiazo-2-yl]-2,2'-bipyridyl (6,6'-bis[5-(biphenyl-4-yl)-1,3,4-oxadiazo-2-yl]-2,2'-bipyridyl : BP-OXD-Bpy), TSPO1(diphenylphosphine oxide-4-(triphenylsilyl)phenyl), It may include TPBi (1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene), tris(8-quinolinolate)aluminum (Alq3), 2,5-diaryl silole derivatives (PyPySPyPy), perfluorinated compounds (PF-6P), COTs (Octasubstituted cyclooctatetraene), etc.

The thickness of the electron injection layer (90) may be 10 nm to 100 nm, more specifically, 20 nm to 50 nm, and the thickness of the electron transport layer (80) may be about 5 nm to 100 nm, for example, 15 nm to 60 nm. When the thicknesses of the electron injection layer (90) and the electron transport layer (80) satisfy the ranges described above, excellent electron transfer characteristics can be obtained without an increase in the driving voltage.

The above hole injection layer (30), hole transport layer (40), electron blocking layer (50), electron injection layer (90), electron transport layer (80), and hole blocking layer (70) may be formed by a method arbitrarily selected from various known methods, such as vacuum deposition, spin coating, spraying, dip coating, bar coating, nozzle printing, slot-die coating, gravure printing, casting, or Langmuir-Blodgett (LB) film method. At this time, the thin film formation conditions and coating conditions may vary depending on the target compound, the structure of the target layer, and thermal characteristics.

The above substrate (10) serves as a support for the light-emitting element and may be a transparent material. In addition, the substrate (10) may be a flexible material or a hard material, and preferably, may be a flexible material.

The material of the above substrate (10) may be, but is not limited to, glass, sapphire, quartz, silicon, polyethylene terephthalate (PET), polystyrene (PS), polyimide (PI), polyvinyl chloride (PVC), polyvinylpyrrolidone (PVP), or polyethylene (PE).

The above substrate (10) may be placed below the positive electrode (20) or may be placed above the negative electrode (100). In other words, the positive electrode (20) may be formed on the substrate before the negative electrode (100), or the negative electrode (100) may be formed before the positive electrode (20). Accordingly, the light-emitting element may have both a regular structure and an inverted structure.

The above-mentioned light-emitting layer (60) is formed between the hole injection layer (30) and the electron injection layer (90), and more specifically, is formed between the electron blocking layer (50) and the hole blocking layer (70), and plays a role in causing light emission by forming excitons when holes (h) introduced from the positive electrode (20) and electrons (e) introduced from the negative electrode (100) combine, and the excitons transition to the ground state and emit light.

In the light-emitting device according to the present invention, the light-emitting layer (60) is characterized by including the non-lead metal halide nanoparticles. Since the non-lead metal halide nanoparticles are as described above in [Non-lead metal halide nanoparticles], detailed descriptions are omitted.

The above-described light-emitting layer (60) can be formed by applying a solution of non-lead halide nanoparticles dispersed in an appropriate organic solvent onto a substrate using a solution process. The solution process used at this time can be formed by a method arbitrarily selected from among various known methods such as spin coating, spray coating, dip coating, gravure coating, reverse offset coating, screen printing, slot-die coating, and nozzle printing.

FIG. 7 shows an energy level diagram of a light-emitting device including lead-free metal halide nanoparticles as a light-emitting layer according to one embodiment of the present invention.

In this specification, energy level means the size of energy. Therefore, even when the energy level is expressed in a minus (-) direction from the vacuum level, the energy level is interpreted as meaning the absolute value of the corresponding energy value. For example, the HOMO energy level means the distance from the vacuum level to the highest occupied molecular orbital. In addition, the LUMO energy level means the distance from the vacuum level to the lowest unoccupied molecular orbital.

In this specification, CBM (conduction band minimum) refers to the lowest point of the conduction band of a material, and VBM (valence band maximum) refers to the highest point of the valence band of a material. The difference between the CBM and VBM is called the bandgap.

Referring to FIG. 7, in the light-emitting device according to the present invention, the energy level (-6.0 eV) of the VBM of the light-emitting layer (60) is preferably lower than the energy levels (-5.2 eV and -5.8 eV, respectively) of the HOMO of the hole injection layer (30) and the hole transport layer (40). When the light-emitting device has such energy levels, when an operating voltage is applied to the light-emitting device, holes (h) from the positive electrode (20) easily flow into the light-emitting layer (60) through the hole injection layer (30).

In addition, in the light-emitting device according to the present invention, it is preferable that the energy level (-3.6 eV) of the CBM of the light-emitting layer (60) is higher than the energy level (-2.7 eV) of the LUMO of the electron transport layer (80). When the light-emitting device has such an energy level, when an operating voltage is applied to the light-emitting device, it becomes easy for electrons (e) from the negative electrode (100) to flow into the light-emitting layer (60) through the electron transport layer (80).

Electrons and holes flowing into the light-emitting layer (60) combine to form excitons, and light is emitted when the excitons transition to the ground state.

In addition, the present invention provides a method for manufacturing a light-emitting device including non-lead metal halide nanoparticles as a light-emitting layer.

The manufacturing method of the above light-emitting device is

A step of forming a negative electrode on a substrate;

A step of forming a hole injection layer on the above negative electrode;

A step of forming a hole transport layer on the above hole injection layer;

A step of forming an electron blocking layer on the above hole transport layer;

A step of forming a light-emitting layer including non-lead metal halide nanoparticles on the electron-blocking layer;

A step of forming a hole-blocking layer on the above-mentioned light-emitting layer;

A step of forming an electron transport layer on the above hole-blocking layer;

A step of forming an electron injection layer on the electron transport layer; and

It includes a step of forming a positive electrode on the electron injection layer.

In the method for manufacturing a light-emitting device according to the present invention, the steps of forming a positive electrode, a hole injection layer, a hole transport layer, an electron blocking layer, a light-emitting layer, a hole blocking layer, an electron transport layer, an electron injection layer, and a positive electrode are as described above, so a detailed description is omitted.

According to the present invention, by nano-sizing a bulk-type lead-free metal halide into a smaller size and reducing the half-width from 30 to 40 nm in the bulk form to 20 to 25 nm, the color purity of the light-emitting device can be improved when used as a light-emitting layer of the light-emitting device.

Hereinafter, preferred manufacturing examples and experimental examples are presented to help understand the present invention. However, the following manufacturing examples and experimental examples are only provided to help understand the present invention, and the present invention is not limited to the following experimental examples.

<Manufacturing Example 1> Cs ₂ Mn(Br _1-a Cl _a ) ₄ (Hereinafter, Cs ₂ Mn(Br/Cl) ₄ Manufacturing of nanoparticles (named as )

(1) Cs ₂ Mn(Br/Cl) ₄ Bulk particle manufacturing

As raw materials, CsBr, CsCl, MnBr ₂ , and MnCl ₂ powders were quantified in a molar ratio of 2-2a:2a:1-a:a, which is the stoichiometric equivalent ratio. Then, the quantified raw materials were mixed and ground for 30 minutes using an agate pestle and mortar in a glove box filled with an argon atmosphere to obtain a mixture. After filling the mixture into a crucible, the crucible filled with the mixture was placed in an alumina tube electric furnace, heated to 650 ℃ under an argon atmosphere, maintained for 24 hours, calcined, and then naturally cooled for 24 hours. Thereafter, the obtained product was pulverized to obtain Cs ₂ Mn(Br/Cl) ₄ bulk particles.

(2) Cs ₂ Mn(Br/Cl) ₄ Manufacturing of nanoparticles

The Cs ₂ Mn (Br/Cl) ₄ bulk particles synthesized in the above (1) were dispersed at a certain concentration in a nonpolar solvent such as hexane, cyclohexane, octane, toluene, chlorobenzene, benzene, chloroform or diethyl ether, and then ultrasonic dispersion was performed using an ultrasonicator. The solution after ultrasonic dispersion was transferred to a 50 ml centrifuge tube, and centrifugation was performed at 8000 rpm for 10 minutes to obtain only the supernatant in which the Cs ₂ Mn (Br/Cl) ₄ nanoparticles were dispersed.

<Comparative Example 1> Cs ₂ Mn(Br/Cl) ₄ Bulk particle manufacturing of

The Cs ₂ Mn(Br/Cl) ₄ bulk particles synthesized in (1) of the above Manufacturing Example 1 were used as is without further nano-processing.

<Manufacturing Example 2> Cs ₂ Mn(Br/Cl) ₄ Manufacturing of light-emitting devices containing nanoparticles as a light-emitting layer

A light-emitting device having the structure shown in Fig. 6 was manufactured using the following method.

First, an ITO substrate (a glass substrate coated with an ITO positive electrode) (20) was prepared as a positive electrode.

A hole injection layer (30) was formed by spin-coating a p-type conductive material, PEDOT:PSS (Heraeus PVP. Al4083), on the ITO substrate (20) and then heat-treating at 145°C for 15 minutes.

Next, a PVK (Poly(n-vinylcarbazole)) solution dissolved in chlorobenzene at 4 mg/ml was applied onto the hole injection layer and spin-coated while rotating at a speed of 3000 rpm. The manufactured thin film was heat-treated at 160°C for 30 minutes to form a hole transport layer (40).

Next, a solution of polyvinylpyrrolidone (PVP) dissolved in isopropyl alcohol was applied onto the hole transport layer (40), spin-coated while rotating at a speed of 5000 rpm, and heat-treated at 100° C. for 5 minutes to form an electron blocking layer (50).

Thereafter, the Cs ₂ Mn(Br/Cl) ₄ nanoparticle dispersion prepared in Manufacturing Example 1 was dispersed in an organic solvent such as hexane, cyclohexane, octane, toluene, chlorobenzene, benzene, chloroform or diethyl ether, and the Cs ₂ Mn(Br/Cl) ₄ nanoparticle dispersion was applied onto the electron-blocking layer (50) and spin-coated while rotating at a speed of 3000 rpm. The prepared thin film was heat-treated at 80° C. for 10 minutes to form a Cs ₂ Mn(Br/Cl) ₄ light-emitting layer (60).

Next, 50 nm thick 1,3,5-Tris(1-phenyl-1Hbenzimidazol-2-yl)benzene (TPBI) was thermally evaporated on the Cs ₂ Mn(Br/Cl) ₄ light-emitting layer (60) in a high vacuum of 1×10 ^-6 Torr or less to form an electron transport layer (80), 1 nm thick LiF was deposited thereon to form an electron injection layer (90), and 100 nm thick aluminum was deposited thereon to form a cathode (100), thereby manufacturing an electroluminescent device using Cs ₂ Mn(Br/Cl) ₄ as the light-emitting layer.

Lastly, the entire surface of the completed electroluminescent device was encapsulated using cover glass and resin to prevent the device from deteriorating in the external environment.

<Comparative Example 2> Cs ₂ Mn(Br/Cl) ₄ Manufacturing of light-emitting devices comprising bulk particles as a light-emitting layer

A light-emitting device was manufactured using the same method as in Manufacturing Example 2, except that the bulk particles of Cs ₂ Mn(Br/Cl) ₄ manufactured in Comparative Example 1 were used in the manufacture of the light-emitting layer.

<Analysis>

FIG. 8 is a diagram comparing photoluminescence and photoexcitation spectra of bulk-type lead-free metal halide particles and lead-free metal halide nanoparticles according to one comparative example and one embodiment of the present invention.

As shown in FIG. 8, for lead-free metal halide particles having the same chemical formula, the bulk-type lead-free metal halide and the lead-free metal halide nanoparticles according to the present invention exhibited photoluminescence excitation at a wavelength prior to 500 nm, and photoluminescence occurred in a green wavelength range of 500 to 550 nm. However, compared to the half-width of the photoluminescence spectrum of the bulk-type lead-free metal halide, the half-width of the lead-free metal halide nanoparticles according to the present invention was reduced to 21 nm, thereby exhibiting high color purity. This effect is an excellent characteristic that has not been reported in conventional lead-free light-emitting devices.

FIG. 9 shows an electroluminescence spectrum according to an applied voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.

As shown in FIG. 9, it was confirmed that the light-emitting device including the lead-free metal halide nanoparticles according to the present invention as a light-emitting layer had an increase in the intensity of the light emission peak as the driving voltage increased, but the half-width was maintained at 21 nm. Accordingly, the light-emitting device including the lead-free metal halide nanoparticles according to the present invention as a light-emitting layer has a narrow half-width and thus can be usefully used as an electroluminescent device exhibiting high color purity.

FIG. 10 is a graph showing the time-resolved photoluminescence results of non-lead metal halide nanoparticles according to one embodiment of the present invention.

As shown in Fig. 10, it was confirmed that a light-emitting device including a non-lead metal halide nanoparticle according to the present invention as a light-emitting layer is capable of electroluminescence by having a short-time resolved photoluminescence characteristic of an average of 6 ns.

FIG. 11 is a graph showing the electroluminescence brightness according to the driving voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.

As shown in Fig. 11, the light-emitting device including the non-lead metal halide nanoparticles according to the present invention as a light-emitting layer showed a difference in brightness at a driving voltage of 10 V or less depending on the difference in the thickness of the light-emitting layer, but showed a tendency for the brightness to increase as the driving voltage increased, and showed a tendency to consistently converge to a high brightness of 10 ² cdm ^-2 or more at a high operating voltage of 10 V or more, thereby confirming high operational stability.

FIG. 12 is a graph showing current density according to driving voltage in a light-emitting device including a non-lead metal halide nanoparticle as a light-emitting layer according to one embodiment of the present invention.

As shown in Fig. 12, a light-emitting device including a non-lead metal halide nanoparticle according to the present invention as a light-emitting layer can be usefully used as an electroluminescent device since the current density increases as the driving voltage increases.

Meanwhile, the embodiments of the present invention disclosed in this specification and drawings are merely specific examples presented to help understanding, and are not intended to limit the scope of the present invention. It will be apparent to those skilled in the art to which the present invention pertains that other modified examples based on the technical idea of the present invention can be implemented in addition to the embodiments disclosed herein.

10: Substrate 20: Positive electrode
30: Hole injection layer 40: Hole transport layer
50: Electron blocking layer 60: Emitting layer
70: Hole blocking layer 80: Electron transport layer
90: Electron injection layer 100: Negative electrode

Claims (15)

Contains a compound represented by the following chemical formula 1,
It has an orthorhombic crystal structure and a space group of Pnma.
The particle size is characterized by being 10 nm or more and less than 20 nm.
Lead-free metal halide nanoparticles.
[Chemical Formula 1]
A ₂ Mn(X ¹ _1-a X ² _a ) ₄
(In the chemical formula 1 above, A is an alkali metal element, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.) In the first paragraph,
A lead-free metal halide nanoparticle characterized in that the compound represented by the chemical formula 1 has a crystal structure comprising MnX ₄ tetrahedra with Mn ²⁺ at the center and four X ¹ , X ^{2 ,} or a combination thereof positioned at each vertex, and A ⁺ ions positioned between them. In the first paragraph,
A non-lead metal halide nanoparticle, characterized in that the compound represented by the above chemical formula 1 is a compound represented by the following chemical formula 2.
[Chemical formula 2]
Cs ₂ Mn(X ¹ _1-a X ² _a ) ₄
(In the above chemical formula 2, X ¹ is Br, X ² is Cl or F, and a is 0 to 1.) In the first paragraph,
The compound represented by the above chemical formula 1 is a lead-free metal halide nanoparticle characterized in that the compound emits light in the green region through the d orbital level of Mn ²⁺ when irradiated with incident light in the ultraviolet to blue region or when voltage is applied. A step for producing a metal halide of the following chemical formula 1 in bulk form;
A step of preparing an ultrasonic dispersion by placing the metal halide of the chemical formula 1 in a nonpolar solvent and dispersing it using ultrasonic waves; and
A step of producing metal halide nanoparticles of the following chemical formula 1 by centrifuging the ultrasonic dispersion and then taking the supernatant.
Method for producing lead-free metal halide nanoparticles.
[Chemical Formula 1]
A ₂ Mn(X ¹ _1-a X ² _a ) ₄
(In the above chemical formula 1,
A is an alkali metal element,
X ¹ is Br,
X ² is Cl or F,
a is between 0 and 1.) In paragraph 5,
The step of manufacturing the metal halide of the above bulk type chemical formula 1 is
A step of obtaining a mixture by mixing raw materials AX ¹ , AX ² , MnX ¹ ₂ , and MnX ² ₂ in a stoichiometric equivalent ratio; and
A method for producing lead-free metal halide nanoparticles, comprising the step of calcining the mixture in an inert gas atmosphere or a reducing atmosphere and then naturally cooling it to obtain a bulk metal halide of chemical formula 1. In paragraph 5,
A method for producing non-lead metal halide nanoparticles, characterized in that the step of producing the ultrasonic dispersion further includes a polar solvent in a non-polar solvent. In paragraph 5,
A method for producing non-lead metal halide nanoparticles, characterized in that the step of producing the ultrasonic dispersion further includes an acid or base additive for pH control in a non-polar solvent. In paragraph 5,
A method for producing non-lead metal halide nanoparticles, characterized in that the non-polar solvent is an aromatic hydrocarbon, an alicyclic hydrocarbon, or an aliphatic hydrocarbon-based organic solvent. A light-emitting device comprising the non-lead metal halide nanoparticles of claim 1 as a light-emitting layer. In Article 10,
A light-emitting element, characterized in that the light-emitting element is a photoluminescent element. In Article 10,
The above light emitting element
positive and negative electrodes;
A light-emitting device characterized by being an electroluminescent device including a light-emitting layer disposed between the positive electrode and the negative electrode. In Article 12,
The above light emitting element
At least one layer of a hole injection layer, a hole transport layer, and an electron blocking layer disposed between the positive electrode and the light-emitting layer,
A light-emitting device characterized by further comprising at least one layer of an electron injection layer, an electron transport layer, and a hole blocking layer disposed between the light-emitting layer and the cathode electrode. In Article 10,
The light-emitting element is characterized in that the light-emitting element has a light emission wavelength of 500 nm to 550 nm when irradiated with incident light in the ultraviolet to blue region or when voltage is applied. In Article 10,
A light-emitting device, characterized in that the half-width of the emission peak of the light-emitting device is 20 to 25 nm.