KR102228142B1 - Quantum dots, methods of manufacturing quantum dots and methods of manufacturing organic light emitting devices using the same - Google Patents

Abstract

In the method of manufacturing a quantum dot, a core is formed using at least one cation precursor and at least one anion precursor. By reacting the shell-forming precursor and the ligand-forming precursor with the core for 1 hour or more, a shell and a ligand surrounding the core are formed. The core, the shell, and the nanoparticles containing the ligand are washed.

Description

Quantum dots, quantum dots manufacturing method, and manufacturing method of an organic light emitting display device using the same {QUANTUM DOTS, METHODS OF MANUFACTURING QUANTUM DOTS AND METHODS OF MANUFACTURING ORGANIC LIGHT EMITTING DEVICES USING THE SAME}

The present invention relates to a quantum dot, a method of manufacturing a quantum dot, and a method of manufacturing an organic light emitting display device using the same.

Quantum dots may include a core, a shell surrounding the core, and a ligand formed on the surface of the shell and chemically bonded thereto. The quantum dots can be obtained by repeatedly washing the core, the shell, and the nanoparticles containing the ligand, but when a weak chemical bonding force is formed between the shell and the ligand, the ligand is lost during the washing process. Can be. Accordingly, the quantum dots may have low quantum efficiency, and an organic light emitting display device including an emission layer formed by using the quantum dots may also have low luminance and low current efficiency. In particular, as the size of the quantum dot is smaller, the quantum dot may have a lower quantum efficiency in proportion thereto.

Meanwhile, a blue quantum dot may have a lower quantum efficiency than a green quantum dot or a red quantum dot. Therefore, in the case of an organic light emitting diode display including a blue quantum dot, relatively higher quantum efficiency may be required.

One object of the present invention is to provide a quantum dot having high quantum efficiency.

Another object of the present invention is to provide a method of manufacturing a quantum dot having high quantum efficiency.

Another object of the present invention is to provide a method of manufacturing an organic light emitting display device having high luminance, low current density, and high current efficiency.

The problem to be solved by the present invention is not limited to the above-described problems, and may be variously expanded without departing from the spirit and scope of the present invention.

In order to achieve an object of the present invention, in the method of manufacturing a quantum dot according to exemplary embodiments, the core is formed by using at least one cation precursor and at least one anion precursor. By reacting the shell-forming precursor and the ligand-forming precursor with the core for about 1 hour or more, a shell and a ligand surrounding the core are formed. The core, the shell, and the nanoparticles containing the ligand are washed.

In example embodiments, when forming the core, a mixture including at least one cation precursor selected from the group consisting of a group 12 element and a group 13 element, an organic solvent, and an unsaturated fatty acid may be formed. The mixture can be heated. At least one anion precursor selected from the group consisting of a group 15 element and a group 16 element may be added to the mixture to react with the cation precursor.

In exemplary embodiments, the cation precursor may include zinc (Zn), cadmium (Cd), or indium (In), and the anion precursor may include sulfur (S), selenium (Se), and tellurium (Te ) Or phosphorus (P).

In example embodiments, the shell-forming precursor may include at least one Group 16 element.

In example embodiments, the ligand-forming precursor may include at least one of oleic acid and trialkylphosphine.

In example embodiments, when reacting the shell forming precursor and the ligand forming precursor with the core, a first shell forming precursor may be reacted with the core to form a first shell surrounding the core. A second shell forming precursor may be reacted with the core and the first shell to form a second shell surrounding the first shell. The ligand-forming precursor may react with the core and the first and second shells to form the ligand on the surface of the second shell.

In example embodiments, the first shell-forming precursor may include at least one Group 16 element.

In example embodiments, the second shell-forming precursor may include at least one Group 12 element and at least one Group 16 element.

In example embodiments, when washing the nanoparticles, the nanoparticles may be precipitated in a non-polar solvent. The nanoparticles may be centrifuged.

In order to achieve another object of the present invention, a quantum dot according to exemplary embodiments includes a core, a first shell and a second shell surrounding the core, and a ligand formed on the surface of the second shell.

In example embodiments, the quantum dot may have a size of about 10 nm or more.

In example embodiments, the first shell may have a layered gradient composition, and the second shell may have a uniform composition.

In example embodiments, each of the first and second shells may include at least one group 12 element and at least one group 16 element.

In exemplary embodiments, the ligand may include oleate.

In exemplary embodiments, the ligand may include oleate and trioctylphosphine (TOP).

In example embodiments, the core may include at least one cation selected from the group consisting of a group 12 element and a group 13 element, and at least one anion selected from the group consisting of a group 15 element and a group 16 element.

In example embodiments, the core may have a blue emission color or a green emission color.

In order to achieve another object of the present invention, in a method of manufacturing an organic light emitting display device according to exemplary embodiments, an anode is formed on a substrate. A hole injection layer is formed on the anode. A hole transport layer is formed on the hole injection layer. A light emitting layer is formed on the hole transport layer using a core, a first shell and a second shell surrounding the core, and a ligand formed on a surface of the second shell, and using quantum dots having a size of about 10 nm or more. An electron transport layer is formed on the emission layer. A cathode is formed on the electron transport layer.

In example embodiments, the hole transport layer may include polyvinylcarbazole (PVK).

In example embodiments, when forming the light emitting layer on the hole transport layer, the quantum dots may be dispersed on the hole transport layer using a solvent containing hexane.

According to exemplary embodiments of the present invention, a quantum dot having high quantum efficiency can be easily formed by controlling a reaction for forming a shell and a ligand when forming a quantum dot. That is, by reacting the ligand-forming precursor and the shell-forming precursor containing oleic acid with the core for about 1 hour or more, the shell can be formed to have a layered gradient composition and a thick thickness, and the ligand can be formed to contain oleate. have. Accordingly, a strong chemical bond may be formed between the ligand and the shell, and since the quantum dots may be formed to have a size of about 10 nm or more, the quantum dots may be formed to have high quantum efficiency. Furthermore, when a shell is additionally formed on the shell surface, the quantum dots may be formed to have higher quantum efficiency. In this case, since the shell, which is additionally formed of a core that determines the quantum efficiency and light emission characteristics of the quantum dot, can be further protected, the quantum dot maintains high quantum efficiency even if the chemical bonding force between the ligand and the shell is partially reduced. I can. Therefore, when manufacturing an organic light-emitting display device, by forming an emission layer using quantum dots formed according to exemplary embodiments of the present invention, the organic light-emitting display device can be manufactured to have high luminance, low current density, and high current efficiency. . In particular, it is possible to solve a problem in which an organic light emitting display device including a blue quantum dot has a relatively lower current efficiency characteristic than an organic light emitting display device including a green or red quantum dot.

1 and 2 are cross-sectional views illustrating quantum dots according to exemplary embodiments of the present invention.
3 is a flowchart illustrating a method of manufacturing a quantum dot according to exemplary embodiments of the present invention.
4 is a flowchart illustrating a method of manufacturing a quantum dot according to other exemplary embodiments of the present invention.
5 is a cross-sectional view illustrating a method of manufacturing an organic light emitting diode display according to exemplary embodiments of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. The same reference numerals are used for the same elements in the drawings, and duplicate descriptions for the same elements are omitted.

1 is a cross-sectional view showing a quantum dot according to exemplary embodiments of the present invention.

Referring to FIG. 1, the quantum dot 100 may include a core 110, a first shell 120, and a ligand 130. The quantum dot 100 may have a size of, for example, about 10 nm or more, and may have a high quantum efficiency in proportion thereto.

The core 110 may have a three-dimensional shape such as a substantially spherical shape at the center of the quantum dot 100, and may include at least one cation and at least one anion. The cation may include a Group 12 element and/or a Group 13 element, and may include, for example, cadmium (Cd), zinc (Zn), and/or indium (In). The anion may include a Group 15 element and/or a Group 16 element, and may include, for example, sulfur (S), selenium (Se), tellurium (Te), and/or phosphorus (P). Accordingly, in exemplary embodiments, the core 110 is a binary core containing CdSe, CdTe, CdS, ZnSe, ZnTe, InP, etc., a ternary system containing ZnCdS, ZnSeTe, CdSeS, ZnCdSe, ZnCdTe, etc. It may be a core, or a four-component core containing ZnCdSeS, ZnCdSeTe, ZnCdTeS, or the like.

Meanwhile, the core 110 may exhibit various colors according to its composition ratio, that is, the contents of the cation and/or the anion. Accordingly, the quantum dot 100 may have various emission colors such as blue, red, and green. In example embodiments, the quantum dot 100 may be a blue quantum dot or a green quantum dot.

The first shell 120 may substantially surround the surface of the core 110 and may include at least one cation and at least one anion. The cation may include, for example, a Group 12 element such as zinc (Zn) and/or cadmium (Cd). The anion may include, for example, a Group 16 element such as sulfur (S). Accordingly, in exemplary embodiments, the first shell 120 may be a binary shell containing ZnS or the like or a ternary shell containing ZnCdS or the like.

In example embodiments, the first shell 120 may have a layered gradient composition. That is, the first shell 120 may have different anion contents and/or different cation contents from an innermost layer to an outermost layer thereof. For example, when the first shell 120 contains zinc (Zn), cadmium (Cd) and sulfur (S), the zinc (Zn) concentration in the first shell 120 is substantially in the innermost layer thereof. It can be the lowest, and it can be substantially the highest at the outermost layer. That is, the zinc (Zn) concentration inside the first shell 120 may substantially increase as the distance from the core 110 increases.

Alternatively, in other exemplary embodiments, the first shell 120 may have a constant composition, for example, the cation content and/or the anion content uniform from the innermost layer to the outermost layer thereof.

Meanwhile, as shown in FIG. 2, the quantum dot 100 may further include a second shell 140 that substantially surrounds the first shell 120 on the surface thereof. In this case, the size of the quantum dot 100 may be further increased, and in particular, bonding between electrons and holes in the core 110 may be further protected. Therefore, the quantum dot 100 can have a higher quantum efficiency, which can be maintained continuously.

The second shell 140 may include at least one cation and at least one anion. The cation may include, for example, a Group 12 element such as zinc (Zn), and the anion may include, for example, a Group 16 element such as sulfur (S). In example embodiments, the second shell 140 may be a binary shell containing ZnS or the like. In this case, the second shell 140 may have a constant composition, for example, the cation content and the anion content uniform from the innermost layer to the outermost layer thereof. The second shell 140 may have a thickness of, for example, about 1.6 nm. The second shell 140 may be a shell substantially different from the first shell 120.

The ligand 130 may include an organic functional group, and may be formed on the surface of the first shell 120 or the second shell 140 to be chemically bonded thereto. The organic functional group may include, for example, oleate and/or trioctylphosphine (TOP).

In exemplary embodiments, when the ligand 130 is formed on the surface of the first shell 120, it may include oleate. Therefore, a strong chemical bond may be formed between the first shell 120 and the ligand 130, and therefore, the ligand 130 may not be lost even during the repeated washing process to obtain the quantum dot 100 when manufacturing it. .

In other exemplary embodiments, when the ligand 130 is formed on the surface of the second shell 140, it may include oleate and TOP. In this case, the chemical bond between the second shell 140 and the ligand 130 may be partially reduced, but the quantum dot 100 further includes the second shell 140 so that the quantum dot 100 is continuously higher than the quantum dot. It can have efficiency. Alternatively, alternatively, even if the ligand 130 is formed on the surface of the second shell 140, it may contain only oleate. In this case, the quantum dot 100 may have a further improved quantum efficiency due to the strong chemical bonding.

3 is a flowchart illustrating a method of manufacturing a quantum dot according to exemplary embodiments of the present invention.

Referring to FIG. 3, a core is formed using at least one cation precursor and at least one anion precursor (step S21).

The core forms a mixture containing the cationic precursor, an organic solvent, and an unsaturated fatty acid including a group 12 element and/or a group 13 element, and the mixture is heated to a temperature of about 100° C. to about 350° C., and then a group 15 element And/or the anion precursor containing a Group 16 element may be added to the heated mixture to react with the cation precursor.

The cationic precursor is, for example, zinc acetylacetonate, zinc acetate, zinc iodide, zinc bromide, zinc chloride, zinc fluoride, dimethyl zinc, diethyl zinc (diethyl zinc), zinc cyanide, zinc hydroxide, zinc carbonate, zinc oxide, zinc chloride, zinc sulfide, cadmium acetylacetonate, cadmium acetate, cadmium iodide, cadmium bromide, chloride Cadmium, cadmium fluoride, dimethyl cadmium, diethyl cadmium, cadmium hydroxide, cadmium carbonate, cadmium oxide, indium acetylacetonate, indium acetate, iodide Indium, indium bromide, indium chloride, indium hydroxide and/or indium carbonate.

The organic solvent is, for example, 1-octadecene (1-oatadecen, 1-ODE), 1-nonadecene, cis-2-methyl-7-octadecene (cis-2-methyl-7 -octadecene), 1-heptadecene, 1-hexadecene, 1-pentadecene, 1-tetradecene, 1-tridecene -tridecene), 1-undecene, 1-dodecene and/or 1-decene.

The unsaturated fatty acids are, for example, lauric acid, palmitic acid, oleic acid, stearic acid, myristic acid, elaidic acid. aicd) and/or a carboxylic acid such as eicosanoic acid.

The anion precursor may be, for example, a mixture containing an element such as sulfur (S), selenium (Se), tellurium (Te), and/or phosphorus (P) and a solvent. In this case, the solvent may include, for example, an alkene such as 1-ODE, an alkylphosphine such as TOP, an oxidized alkylphosphine such as trioctylphosphineoxide (TOPO), or an amine.

Accordingly, in exemplary embodiments, the core is a binary core containing CdSe, CdTe, CdS, ZnSe, ZnTe, InP, etc., a ternary core containing ZnCdS, ZnSeTe, CdSeS, ZnCdSe, ZnCdTe, and the like, Alternatively, it may be formed of a four-component core containing ZnCdSeS, ZnCdSeTe, ZnCdTeS, or the like.

On the other hand, the quantum dots may have various emission colors such as blue, red, and green depending on the color of the core, which can be adjusted by changing the composition ratio of the core, that is, the content of the cation precursor and/or the content of the anion precursor. . Alternatively, alternatively, the emission color may be adjusted by changing the size of the core. In example embodiments, a blue quantum dot or a green quantum dot may be formed.

Thereafter, the shell-forming precursor and the ligand-forming precursor are reacted with the core for about 1 hour to about 12 hours, thereby forming a shell and a ligand surrounding the core (step S22). At this time, the ligand may be formed on the shell surface.

The shell forming precursor may include at least one Group 16 element, and may include, for example, sulfur (S) and/or selenium (Se). Accordingly, in exemplary embodiments, the shell may be formed of a binary shell such as ZnS or a ternary shell such as ZnCdS.

Meanwhile, the thickness of the shell and the internal composition ratio thereof may be determined by a reaction time between the core and the shell-forming precursor. That is, as the reaction time increases, the shell may be formed to have a thicker thickness and a layered gradient composition. Therefore, when the shell-forming precursor and the core are reacted for about 1 hour or more, the core, the shell, and the nanoparticles including the ligand may be formed to have a size of about 10 nm or more, and accordingly, the quantum dots have high quantum efficiency. It can be formed to have. In addition, the shell may be formed to have different compositions from the innermost layer to the outermost layer thereof.

In exemplary embodiments, when the shell is formed to contain zinc (Zn), cadmium (Cd), and sulfur (S), it has a zinc (Zn) concentration that increases substantially as it moves away from the core. Can be formed. That is, the shell may be formed to have the lowest zinc (Zn) concentration in the innermost layer thereof and the highest zinc (Zn) concentration in the outermost layer.

Or alternatively, the shell may be formed to have a certain composition.

The ligand-forming precursor may include, for example, oleic acid. Accordingly, in exemplary embodiments, the ligand may be formed to include an oleic acid salt derived from the oleic acid. In this case, a strong chemical bond may be formed between the shell and the ligand, and thus the ligand may not be lost during the subsequent washing process of the nanoparticles.

Thereafter, the nanoparticles are washed (step S23). Accordingly, the nanoparticles may be purified to prepare the quantum dots.

In exemplary embodiments, the quantum dots may be prepared by precipitating the nanoparticles in a non-polar solvent and performing a centrifugal separation process using a complex solvent. In this case, the non-polar solvent may include, for example, ethanol or acetone, and the complex solvent may include acetone and chloroform. Such a washing process may be repeatedly performed three or more times, for example.

As described above, the quantum dots having high quantum efficiency can be easily formed by controlling the reaction for forming the shell and the ligand. That is, by reacting the ligand-forming precursor containing oleic acid and the shell-forming precursor with the core for about 1 hour or more, the shell may be formed to have a layered gradient composition and a thick thickness, and the ligand may contain oleate. Can be formed. Accordingly, a strong chemical bond may be formed between the ligand and the shell, and since the quantum dots may be formed to have a size of about 10 nm or more, the quantum dots may be formed to have high quantum efficiency.

In particular, when a blue quantum dot is formed through processes according to exemplary embodiments, a problem in which a blue quantum dot has a relatively very low quantum efficiency compared to a red or green quantum dot can be solved.

4 is a flowchart illustrating a method of manufacturing a quantum dot according to exemplary embodiments of the present invention. The quantum dot may be formed by performing substantially the same or similar processes to the manufacturing method described with reference to FIG. 3. Accordingly, detailed descriptions of the same components will be omitted.

Referring to FIG. 4, a core is formed by performing substantially the same process as in step S21 of FIG. 3 (step S31). Accordingly, the core may be formed substantially the same as the core described with reference to FIG. 3.

Subsequently, a first shell surrounding the core is formed by performing substantially the same process as in step S22 of FIG. 3 (step S32). That is, the first shell may be formed by reacting the first shell forming precursor substantially the same as the shell forming precursor described with reference to FIG. 3 with the core, which is formed substantially the same as the shell described with reference to FIG. Can be.

Thereafter, by reacting the second shell forming precursor with the core and the first shell, a second shell surrounding the first shell is formed (step S33). Accordingly, the quantum dot may be formed to have a larger size than the quantum dot described with reference to FIG. 3, and since the bonding between electrons and holes in the core may be further protected, it may be formed to have higher quantum efficiency.

The second shell forming precursor may include at least one cation precursor and at least one anion precursor. The cation precursor may include, for example, a Group 12 element such as zinc (Zn), and the anion precursor may include, for example, a Group 16 element such as sulfur (S).

In exemplary embodiments, the second shell may be formed of a binary shell such as ZnS, may be formed to have a uniform composition, and may be formed to have a thickness of about 1.6 nm. The second shell may be formed substantially different from the first shell. Meanwhile, the thickness of the second shell may vary depending on the reaction time between the core, the first shell, and the second shell forming precursor, and thus the thickness is not limited thereto, and the quantum characteristics of the quantum dot to be formed It can be easily changed according to.

Thereafter, a ligand-forming precursor is reacted with the core and the first and second shells to form a ligand on the surface of the second shell (step S34).

The ligand-forming precursor may include, for example, oleic acid and trialkylphosphine. Accordingly, in exemplary embodiments, the ligand may be formed to include the oleate derived from the oleic acid and the TOP derived from the trialkylphosphine. In this case, the chemical bonding force between the ligand and the second shell may be partially reduced, but the quantum dots may not be formed to have a reduced quantum efficiency due to the formation of the second shell.

Alternatively, the ligand-forming precursor may contain only oleic acid, and accordingly, in other exemplary embodiments, the ligand may be formed to contain only oleic acid salt. In this case, due to the strong chemical bond, the quantum dots may be formed to have higher quantum efficiency.

Thereafter, the core, the first and second shells, and the nanoparticles including the ligand are washed by performing substantially the same process as in step S23 of FIG. 3 (step S35). Accordingly, the nanoparticles may be purified to prepare the quantum dots.

As described above, when the second shell is additionally formed during quantum dot manufacturing, the quantum dot may have higher quantum efficiency. That is, since the core, which determines the quantum efficiency and luminescence characteristics of the quantum dot, can be further protected by the second shell, even if the chemical bond between the second shell and the ligand is partially reduced, the quantum dot is continuously high. It can have quantum efficiency.

5 is a cross-sectional view illustrating a method of manufacturing an organic light emitting diode display 200 according to exemplary embodiments of the present invention.

Referring to FIG. 5, an anode 220, a hole injection layer (HIL) 230, and a hole transport layer (HTL) 240 are sequentially formed on a substrate 210.

The anode 220 may be formed by forming a first conductive film on the substrate 210 through a deposition process such as sputtering, and patterning it. In this case, the first conductive layer may be formed of a metal or metal oxide, and may be formed of, for example, indium tin oxide (ITO), zinc oxide, indium oxide, tin oxide, indium zinc oxide, or the like.

Thereafter, a cleaning process may be performed on the substrate 210 on which the anode 220 is formed.

In exemplary embodiments, the cleaning process may be performed through a wet cleaning process and/or an ultraviolet ozone treatment process using deionized water (DI), acetone and/or isopropanol.

The hole injection layer (HIL) 230 may be formed by applying a composition including a hole injection material on the anode 220 and soft baking the substrate 210 on which the composition is applied. In this case, the hole injection material may include, for example, poly(3, 4-ethylenedioxylenethiophene) (PEDOT) and/or polystyrene sulfonate (PSS). In exemplary embodiments, the hole injection layer (HIL) 230 is spin coating, inkjet printing, nozzle printing, spray coating, and slit coating. coating), dip coating, etc. to have a thickness of about 20 nm.

The hole transport layer (HTL) 240 may be formed by applying a composition including a hole transport material on the hole injection layer (HIL) 230 and soft baking the composition. In this case, the hole transport material is, for example, polyvinylcarbazole PVK, NPD (N,N'-diphenyl-N,N'-bis(1-naphthylphenyl)-1,1'-biphenyl-4, 4'-diamine), poly-TPD(poly(N,N'-bis(4-butylphenyl)-N-N'-bis(phenyl-benzidine))), poly-TFB(poly[(9,9-dioctylfluorenyl- 2,7-diyl)-co-(4,4'-(N-(4-sec-butylphenyl))diphenyl-amine)]) and/or PPV (poly(1,4-phenylenevinylene)). In an exemplary embodiment, the hole transport layer (HTL) 240 may be formed to have a thickness of about 20 nm through spin coating, inkjet printing, nozzle printing, spray coating, slit coating, dip coating, or the like.

Meanwhile, the substrate 210 may include, for example, a glass substrate, a quartz substrate, a plastic substrate, a ceramic substrate, or a semiconductor substrate. Alternatively, the substrate 210 may include a flexible substrate.

Thereafter, the light emitting layer 250 is formed on the hole transport layer (HTL) 240.

In exemplary embodiments, the light emitting layer 250 is coated on the hole transport layer (HTL) 240 by dispersing the quantum dots 100 in a solvent such as water, hexane, chloroform, and toluene, and then spin coating. It can be formed by doing. Meanwhile, when the hole transport layer (HTL) 240 is formed to include PVK as a hole transport material, it may be dissolved by a solvent of chloroform and/or toluene. Therefore, the solvent may not contain chloroform and/or toluene, and may contain, for example, hexane.

The quantum dot 100 may include the quantum dots described with reference to FIGS. 1 and/or 2, which can be manufactured by performing the processes described with reference to FIG. 3 or 4. Accordingly, the emission layer 250 may have high emission characteristics, and the organic light emitting display device 200 including the same may be manufactured to have high luminance, low current density, and high current efficiency.

Thereafter, an electron transport layer (ETL) 260 and a cathode 270 are sequentially formed on the emission layer 250.

The electron transport layer (ETL) 260 may be formed by applying a composition including an electron transport material on the light emitting layer 250 and soft baking the composition. In this case, the electron transport material may include, for example, ZnO quantum dots and/or TiO2 nanoparticles. Alternatively, it includes BCP (2,9-dimethyl-4,7-diphenyl-1,10-phenanhro-line) and/or TPBI (1,3,5-tris(N-phenylbenzimidazol-2,yl)benzene). You may. In example embodiments, the electron transport layer (ETL) 260 may be formed to have a thickness of about 50 nm through spin coating, inkjet printing, nozzle printing, spray coating, slit coating, dip coating, or the like.

The cathode 270 may be formed by forming a second conductive layer on the electron transport layer (ETL) 260 through a deposition process such as a thermal evaporation process, and patterning the second conductive layer. In this case, the second conductive layer may be formed to include, for example, a metal such as calcium (Ca), aluminum (Al), magnesium (Mg), silver (Ag), barium (Ba), a metal alloy, or a metal oxide. .

As described above, the emission layer 250 may be formed using the quantum dots 100 according to exemplary embodiments of the present invention, and accordingly, the organic light emitting display device 200 including the emission layer 250 is It can be manufactured to have luminance, low current density and high current efficiency. In particular, when the quantum dot 100 is a blue quantum dot, the organic light emitting display device 200 including the same may be manufactured to have substantially the same or superior electrical characteristics as an organic light emitting display device including a green or red quantum dot. .

Furthermore, by forming the hole transport layer (HTL) 240 of polyvinyl carbazole at an inexpensive price, the organic light emitting display device 200 including the hole transport layer (HTL) 240 may secure price competitiveness.

Experimental Example 1

1 mmol of cadmium oxide and 10 mmol of zinc acetate were placed in a three-necked flask, 15 ml of 1-octadecene (1-ODE) and 7 ml of oleic acid were added to form a first mixture, and the first mixture was heated to 150° C. in a vacuum state. Then, it was heated to 310°C again under an argon atmosphere. Then, 1.6 mmol of sulfur powder was added to 2.4 ml of 1-ODE to form a second mixture, and the second mixture was added to the heated first mixture and reacted for 12 minutes. Accordingly, a ZnCdS core was formed. Thereafter, 4 mmol of sulfur powder was added to 5 ml of oleic acid to form a third mixture, and this third mixture was reacted with the core by dropwise dropping it on the surface of the core. The reaction was maintained for 1 hour. Accordingly, nanoparticles including a ZnS or ZnCdS shell and an oleate ligand were formed. Thereafter, the nanoparticles were precipitated with acetone and then centrifuged using a complex solvent containing hexane and ethanol. Accordingly, blue quantum dots having a size of about 12 nm and including a ZnCdS core, a ZnCdS shell having a layered gradient composition, and an oleate ligand were obtained.

Experimental Example 2

A quantum dot was obtained by performing substantially the same processes as in Experimental Example 1, except that the reaction of the third mixture and the core was maintained for 2 hours.

Experimental Example 3

A quantum dot was obtained by performing substantially the same processes as in Experimental Example 1, except that the reaction of the third mixture and the core was maintained for 4 hours.

Experimental Example 4

Substantially as in Experimental Example 1, except that the first mixture was formed using 0.14 mmol of cadmium acetate and 3.41 mmol of zinc oxide, and the second mixture was formed using 5 ml of TOP, 5 ml of oleic acid, 5 mmol of selenium powder and 5 mmol of sulfur powder. By performing the same process as to obtain a quantum dot. Quantum dots having such a green light-emitting color had a size of about 10 nm, and included a CdSe core, a ZnCdS shell having a layered gradient composition, an oleate and a TOP ligand.

Experimental Example 5

By performing substantially the same process as in Experimental Example 4, first nanoparticles including a CdSe core and a ZnCdS first shell having a layered gradient composition and having a green light emission color were formed. Thereafter, a fourth mixture was formed by adding 2.36 mmol of zinc acetate dehydrate to 1 ml of oleic acid and 4 ml of 1-ODE, and the fourth mixture was reacted with the first nanoparticles at a temperature of about 310°C. And the reaction was maintained until the temperature was lowered to 270°C. Thereafter, 9.65 mmol of sulfur powder was added to 5 ml of TOP to form a fifth mixture, and the fifth mixture was reacted with the fourth mixture and the first nanoparticles for about 20 minutes. Accordingly, a ZnS second shell was formed surrounding the first nanoparticles and having a thickness of about 1.96 nm, and a ligand including oleate and TOP was formed on the surface of the second shell. Thereafter, the core, the first and second shells, and the second nanoparticles including the ligand were washed by performing substantially the same process as in Experimental Example 1. Accordingly, a green quantum dot including the core, the first and second shells, and the ligand and having a size of about 13 nm was obtained.

Comparative Example 1

A quantum dot was obtained by performing substantially the same process as in Experimental Example 1, except that the reaction of the third mixture and the core was maintained for 40 minutes.

Comparative Example 2

A quantum dot was obtained by performing substantially the same process as in Experimental Example 1, except that the third mixture was formed using TOP. Accordingly, a blue quantum dot having a size of about 12 nm and including a ZnCdS core, a ZnCdS shell having a layered gradient composition, and a TOP ligand was obtained.

Comparative Example 3

The reaction time of the third mixture and the core was maintained for 4 hours, and substantially the same process as in Experimental Example 1 was performed, except that the third mixture was formed using TOP to obtain quantum dots.

Experimental Example 6

A first conductive film was formed by depositing indium tin oxide (ITO) on a substrate, and an anode was formed by patterning it. Subsequently, the substrate on which the anode was formed was washed with acetone and methanol for about 20 minutes, and ozone treatment was performed for 15 minutes, and thus PEDOT-PSS (clevios) having a relatively high conductivity on the washed anode. PH500) and a compound containing PEDOT-PSS (clevios AI4083) having a relatively low conductivity was spin-coated and then soft baked at 110°C for 30 minutes in a glove box under a nitrogen atmosphere to form a hole injection layer. . After dissolving 5 ml of 0.05 g of polyvinylcarbazole in chlorobenzene to prepare a 1.1 vol% polyvinylcarbazole solution, the solution was spin-coated on the hole injection layer at 3000 rpm for 60 seconds, and this was performed under a nitrogen atmosphere. A hole transport layer was formed by soft baking in a glove box at a temperature of 150° C. for 30 minutes. At this time, the hole transport layer was formed to a thickness of about 20 nm. Thereafter, the quantum dots obtained according to Experimental Example 1 were dispersed in hexane to prepare a first quantum dot solution having a concentration of 15 mg/ml, and the first quantum dot solution was spin-coated on the hole transport layer at 2000 rpm for 20 seconds to about 20 nm. A light emitting layer having a thickness of was formed. After that, no additional soft baking process was performed. Subsequently, ZnO quantum dots were dispersed in ethanol to prepare a second quantum dot solution having a concentration of 20 mg/ml, and the second quantum dot solution was spin-coated on the emission layer at 1500 rpm for 60 seconds, and then in a glove box under a nitrogen atmosphere. The electron transport layer was formed by soft baking at a temperature of 110° C. for 30 minutes. At this time, the electron transport layer was formed to a thickness of about 50 nm. Aluminum (Al) was deposited to a thickness of 100 nm on the electron transport layer by thermal evaporation to form a second conductive film, and then patterned to form a cathode. Accordingly, a blue quantum dot organic light emitting display device was manufactured.

Experimental Example 7

An organic light-emitting display device was manufactured by performing substantially the same processes as in Experimental Example 6, except that the emission layer was formed by using the quantum dots according to Experimental Example 2.

Experimental Example 8

An organic light-emitting display device was manufactured by performing substantially the same processes as in Experimental Example 6, except that the emission layer was formed using the quantum dots according to Experimental Example 3.

Experimental Example 9

An organic light emitting display device was manufactured by performing substantially the same processes as in Experimental Example 6, except that the emission layer was formed using the quantum dots using the quantum dots according to Experimental Example 4.

Experimental Example 10

An organic light emitting display device was manufactured by performing substantially the same processes as in Experimental Example 6, except that the emission layer was formed using the quantum dots using the quantum dots according to Experimental Example 5.

Comparative Example 4

An organic light emitting display device was manufactured by performing substantially the same processes as in Experimental Example 6, except that the emission layer was formed using the quantum dots according to Comparative Example 3.

Evaluation of quantum efficiency of quantum dots according to reaction time for shell and ligand formation

In order to evaluate the quantum efficiency of the quantum dots according to the reaction time for the formation of the shell and the ligand during the production of the quantum dots, the sizes of the quantum dots were measured through TEM for Experimental Examples 1 to 3 and Comparative Example 1, and quantum efficiencies were measured. And the results are shown in Table 1 below.

Quantum dots Quantum dot size (nm) Quantum efficiency (%) Experimental Example 1 10-12 73 Experimental Example 2 10-12 87 Experimental Example 3 12-13 109 Comparative Example 1 8 38

Referring to Table 1, it was confirmed that the quantum dots according to Experimental Examples 1 to 3 had a size of 10 nm or more and high quantum efficiency. Therefore, it can be seen that the longer the reaction time for the formation of the shell and the ligand, the larger the size of the formed quantum dots, and is formed to have a uniform size distribution and have a spherical shape. In addition, it can be seen that the quantum efficiency of the quantum dot also gradually increases as the reaction time increases.

Quantum efficiency evaluation of quantum dots according to ligand type

In order to evaluate the quantum efficiency of quantum dots according to the type of ligand, the quantum dots according to Experimental Example 1 and Comparative Example 2 were repeatedly washed, and then their quantum efficiency was measured, and the results are shown in Table 2 below.

Quantum dots Number of washing Quantum efficiency (%) Experimental Example 1 0 times 73 1 time 73 Episode 2 73 3rd time 73 Comparative Example 2 0 times 73 1 time 69 Episode 2 58 3rd time 54

Referring to Table 2, the quantum efficiency of the quantum dot according to Experimental Example 1 did not decrease even after performing the repeated washing process, but the quantum efficiency of the quantum dot according to Comparative Example 2 was rapidly decreased as the number of times of the washing process increased. I could confirm that. Therefore, it was found that a strong chemical bonding force was formed between the shell and the ligand of the quantum dot according to Experimental Example 1, which was found to have consistently excellent quantum properties.

Quantum efficiency evaluation of quantum dots according to additional shell formation

In order to evaluate the quantum efficiency of the quantum dots due to the formation of an additional shell, the initial quantum efficiency of the quantum dots according to Experimental Examples 4 and 5 was measured, and then the quantum efficiency changes were measured by performing the repeated washing process, respectively, and the result Is shown in Table 3 below.

Quantum dots Number of washing Quantum efficiency (%) Experimental Example 4 0 times 43 Episode 2 38 4 times 36 6 times 35 8 times 34 Experimental Example 5 0 times 84 Episode 2 84 4 times 84 6 times 84 8 times 84

Referring to Table 3, it was confirmed that the quantum dots according to Experimental Example 5 not only had higher quantum efficiency than the quantum dots according to Experimental Example 4, but also maintained high quantum efficiency continuously even after repeated washing processes were performed. Therefore, a quantum dot having higher quantum efficiency can be manufactured by additionally forming a shell surrounding the core, and in this case, in particular, even if the chemical bonding force between the shell and the ligand of the quantum dot is partially reduced, the quantum dot can continue to have high quantum efficiency. You can see that there is.

Evaluation of characteristics of organic light-emitting display devices according to emission layers I

In order to evaluate the characteristics of the organic light-emitting display device according to the emission characteristics of the emission layer, the maximum current efficiency and the maximum external quantum efficiency were measured for the organic light-emitting display devices according to Experimental Examples 6 to 10, and the results are shown in Table 4 below. .

Organic light emitting display Maximum current efficiency (cd/A) Maximum external quantum efficiency (%) Experimental Example 6 0.4 1.1 Experimental Example 7 0.7 1.8 Experimental Example 8 2.2 7.1 Experimental Example 9 2.1 0.5 Experimental Example 10 46.4 12.6

Referring to Table 4, it was confirmed that as the reaction time of forming the shell and ligand of the quantum dots forming the emission layer increased, the maximum current efficiency and the maximum external quantum efficiency of the organic light emitting display device including the emission layer increased (Experimental Example 6 To 8). In addition, it was confirmed that the organic light emitting display device manufactured by using a quantum dot further including an additional shell has a higher maximum current efficiency and a maximum external quantum efficiency (see Experimental Examples 9 and 10).

Therefore, the light-emitting layer may have an increased light-emitting property in proportion to the reaction time for forming the shell and ligand of the quantum dot, and furthermore, when the quantum dot further includes an additional shell, it may have higher light-emitting properties. It can be seen that the included organic light emitting diode display exhibits excellent electrical characteristics such as high luminance, low current density value, and high current efficiency.

Evaluation of the characteristics of an organic light emitting diode display according to the characteristics of the emission layer II

In order to evaluate the characteristics of the organic light-emitting display device according to the emission characteristics of the emission layer, the maximum luminance and maximum current efficiency were measured for the organic light-emitting display devices according to Experimental Examples 8 to 10 and Comparative Example 4, and the results are shown in Table 5 below. Shown in.

Organic light emitting display Maximum luminance (cd/m ² ) Maximum current efficiency (cd/A) Experimental Example 8 2624 2.2 Experimental Example 9 9010 2.1 Experimental Example 10 85700 46.4 Comparative Example 4 379 0.3

Referring to Table 5, the organic light-emitting display device according to Comparative Example 4 exhibited very low luminance and current efficiency, while the organic light-emitting display device according to Experimental Example 8 improved the maximum luminance by about 7 times and about 10 times that of Comparative Example 4. It was confirmed that the maximum current efficiency was improved. In addition, it was confirmed that the organic light emitting display device according to Experimental Example 10 exhibited a maximum luminance improved by about 10 times and a maximum current efficiency improved by about 13 times compared to the organic light emitting display device according to Experimental Example 9.

Therefore, it can be seen that the electrical characteristics of the OLED display can be improved in proportion to the kind of the ligand of the quantum dot forming the emission layer, that is, the chemical bonding force between the shell and the ligand of the quantum dot. In addition, it can be seen that an organic light emitting display device having more improved electrical characteristics can be manufactured by forming an emission layer using quantum dots further including an additional shell.

The present invention can be applied to all electronic devices including quantum dots and organic light emitting display devices including the same. For example, the present invention provides not only stationary electronic devices such as monitors, televisions, and digital information display (DID) devices, but also notebooks, digital cameras, mobile phones, smart phones, smart pads, and PDAs. , PMP, MP3 players, navigation systems, camcorders, portable electronic devices such as portable game consoles.

Although the above has been described with reference to embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention within the scope not departing from the spirit and scope of the present invention described in the following claims. You will understand that you can.

100: quantum dot 110: core
120: shell 130: ligand
200: organic light emitting display device 210: substrate
220: anode 230: hole injection layer
240: forward transport layer 250: light emitting layer
260: electron transport layer 270: cathode

Claims (20)

Forming a core using at least one cation precursor and at least one anion precursor;
Forming a first shell surrounding the core by reacting a first shell-forming precursor with the core;
Forming a second shell surrounding the first shell by reacting a second shell-forming precursor with the core and the first shell;
Reacting a ligand-forming precursor with the core, the first shell, and the second shell to form a ligand on the surface of the second shell; And
Including the step of washing the nanoparticles containing the core, the first shell, the second shell, and the ligand,
The method of manufacturing a quantum dot, wherein the first shell has a layered gradient composition, and the second shell has a uniform composition. The method of claim 1, wherein forming the core comprises:
Forming a mixture comprising at least one of the cationic precursors selected from the group consisting of a group 12 element and a group 13 element, an organic solvent, and an unsaturated fatty acid;
Heating the mixture; And
A method of manufacturing a quantum dot, comprising the step of reacting with the cation precursor by adding at least one anion precursor selected from the group consisting of a group 15 element and a group 16 element to the mixture. The method of claim 1, wherein the cation precursor comprises zinc (Zn), cadmium (Cd) or indium (In), and the anion precursor is sulfur (S), selenium (Se), tellurium (Te), or phosphorus ( P) a method for producing a quantum dot, characterized in that it comprises. The method of claim 1, wherein the first shell-forming precursor and the second shell-forming precursor contain at least one group 16 element. The method of claim 1, wherein the ligand-forming precursor comprises at least one of oleic acid and trialkylphosphine. delete The method of claim 1, wherein the first shell-forming precursor contains at least one Group 16 element. The method of claim 1, wherein the second shell-forming precursor comprises at least one group 12 element and at least one group 16 element. The method of claim 1, wherein the washing of the nanoparticles,
Precipitating the nanoparticles in a non-polar solvent; And
A method of manufacturing a quantum dot, comprising the step of centrifuging the nanoparticles. core;
A first shell and a second shell surrounding the core; And
Including a ligand formed on the surface of the second shell,
The first shell has a layered gradient composition, and the second shell has a uniform composition. The quantum dot of claim 10, wherein the quantum dot has a size of 10 nm or more. delete 11. The quantum dot of claim 10, wherein the first and second shells each contain at least one group 12 element and at least one group 16 element. The quantum dot according to claim 10, wherein the ligand comprises oleate. The quantum dot according to claim 10, wherein the ligand comprises oleate and trioctylphosphine (TOP). The quantum dot according to claim 10, wherein the core comprises at least one cation selected from the group consisting of a group 12 element and a group 13 element, and at least one anion selected from the group consisting of a group 15 element and a group 16 element. . 11. The quantum dot of claim 10, wherein the core has a blue emission color or a green emission color. Forming an anode on the substrate;
Forming a hole injection layer on the anode;
Forming a hole transport layer on the hole injection layer;
Forming a light emitting layer on the hole transport layer using a core, a first shell and a second shell surrounding the core, and a ligand formed on a surface of the second shell, and using quantum dots having a size of 10 nm or more;
Forming an electron transport layer on the emission layer; And
Including the step of forming a cathode on the electron transport layer,
The first shell has a layered gradient composition, and the second shell has a uniform composition. 19. The method of claim 18, wherein the hole transport layer comprises polyvinylcarbazole (PVK). The organic light emitting diode display of claim 18, wherein forming the emission layer on the hole transport layer comprises dispersing the quantum dots on the hole transport layer using a solvent containing hexane. Manufacturing method.

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