JP6290232B2 - Luminescent quantum dot - Google Patents

Description

  The present invention relates to a light emitting quantum dot, and in particular, a ligand for capping a quantum dot contains a light emitting substance whose color is changed by pH change, and has excellent dispersibility and stability on an aqueous solution. The present invention relates to a light-emitting quantum dot that is excellent in color purity and light-emitting characteristics when applied to the same, and a method for producing the same.

A quantum dot is a nano-sized semiconductor material and exhibits a quantum restriction effect. When such a quantum dot receives light from an excitation source and reaches an energy excited state, Voluntarily releases energy by the corresponding energy band gap. In addition, by adjusting the size of the quantum dot and adjusting the corresponding band gap, the electrical and optical characteristics can be adjusted. Therefore, the emission wavelength can be adjusted only by adjusting the size of the quantum dot, which is excellent. Therefore, the present invention can be applied to various elements such as a light emitting element or a photoelectric conversion element.
Quantum dots as light-emitting elements that have been studied in the past are difficult to use as light-emitting elements because their dispersibility and stability are reduced on aqueous solutions, and their color purity and light-emitting properties are reduced. It is impossible to emit white light with only quantum dots, and it is difficult to provide a separate filter layer to change the wavelength of the emitted light in order to realize white light. However, the fact is that no quantum dot that emits white light by itself has been reported in spite of many needs.

  In order to solve the above-described problems, the present invention can emit white light by itself, has excellent dispersibility and stability on an aqueous solution, and has color purity and light emission characteristics when applied to a light emitting device. An object is to provide an excellent light emitting quantum dot, a method for producing the same, and a light emitting device including the same.

In order to achieve the above object, the present invention provides:
A quantum dot comprising a core / shell structure and a ligand attached to the surface of the shell, comprising:
Provided is a quantum dot including a light emitting group in which the ligand is color-converted by pH change.

  In addition, the present invention includes a step of adding a ligand including a light emitting group that is color-converted by pH change to a solution in which a core / shell structure is dispersed, and then stirring the light emitting quantum dot. Provide a method.

  According to another aspect of the present invention, there is provided a light emitting device including the light emitting quantum dot as a light emitting material.

  According to another aspect of the present invention, there is provided a method for manufacturing a light emitting device, comprising the step of forming a light emitting layer with the light emitting quantum dots.

  The light-emitting quantum dot according to the present invention has excellent dispersibility and stability on an aqueous solution and can emit white light by itself even without a separate filter layer. And can be made to have excellent color purity, high stability, and high luminous efficiency as compared with conventional light-emitting elements.

The color change by pH of the light emission group of this invention is shown. The PL spectrum by pH of the light emission group of this invention is shown. FIG. 6 illustrates that the quantum dot according to an embodiment of the present invention can achieve white light emission through pH adjustment. FIG. 3 illustrates that a quantum dot according to an embodiment of the present invention can emit B—O white light. 4 shows that a quantum dot according to an embodiment of the present invention can emit white light having a color purity close to that of a standard light source while moving to a blue-green wavelength. 2 illustrates that a quantum dot according to an embodiment of the present invention can emit white light of R-GB system. 1 is a method for synthesizing a core / shell structure according to an embodiment of the present invention. 1 is a method for manufacturing a light emitting device according to an embodiment of the present invention. 3 shows an EL spectrum of a light emitting device according to an embodiment of the present invention. 4 is a result of measuring current density-voltage-luminance (IV-L) characteristics of a light emitting device according to an embodiment of the present invention using a Keithley-236 source-measurement unit.

The present invention will be described in detail below.
The light-emitting quantum dots of the present invention are
A quantum dot comprising a core / shell structure and a ligand attached to the surface of the shell, comprising:
The ligand includes a light emitting group that is color-converted by pH change.
The ligand includes a light emitting group and a connecting group that connects the shell and the light emitting group, and may include a spacer between the connecting group and the light emitting group as necessary.
The following structural formula 1 shows a schematic diagram of a light-emitting quantum dot according to an embodiment of the present invention.
[Structural Formula 1]

In the structural formula 1, A represents a light emitting group, L represents a spacer, and X represents a connected group.

In the light emitting quantum dot of the present invention, a known core / shell structure can be used as the core / shell structure, and the core / shell structure described in Korean Patent Publication No. 2010-35466 is used as an example. You can also. More specifically, the core / shell structure is selected from a) a first element selected from Group 2, 12, 12, 13 and 14 and a second element selected from Group 16; b) selected from Group 13 An element selected from the group consisting of: a first element selected from the group consisting of the first element selected from the group 15; and a group 14 element selected from the group 14 element; or a material that forms a core / shell structure. Examples thereof include MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS, SrSe, SrTe, BaO, BaS, BaSe, BaTE, ZnO, ZnS, ZnSe, ZnTe, CdO , CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, Al ₂ O ₃ , Al ₂ S ₃ , Al ₂ Se ₃ , Al ₂ Te ₃ , Ga ₂ O ₃ , Ga ₂ S ₃ , Ga ₂ Se ₃ , Ga ₂ Te ₃ , In ₂ O ₃ , In ₂ S ₃ , In ₂ Se ₃ , In ₂ Te ₃ , SiO ₂ , GeO ₂ , SnO ₂ , SnS, SnSe, One or more selected from the group consisting of SnTe, PbO, PbO ₂ , PbS, PbSe, PbTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs, InSb, BP, Si, Ge These can be used in which a core / shell structure is formed.

  The average diameter of the core / shell structure can be arbitrarily adjusted, and 1 to 12 nm can be used. Preferably, the core / shell structure that emits light in the region of 500 to 800 nm has a diameter of 5 to 12 nm, and the core / shell structure that emits light in the region of 400 to less than 500 nm has a diameter of 1-3 nm. It can be made to have.

  In the light emitting quantum dot of the present invention, a light emitting group which is color-converted by pH change can be applied as the light emitting group.

  As the light emitting group, a known light emitting group that is color-converted by pH change can be used.

  In the luminescent quantum dot of the present invention, the linking group is not particularly limited as long as the linking group is a linking group attached to the shell and connected to the luminescent group or the spacer. For example, a sulfo group, a thiol group , A carboxy group, an amine group, a phosphine group, and a group selected from the group consisting of phosphide groups can be used. Preferably, the linking group is a sulfo group.

The light emitting quantum dot of the present invention may further include a spacer between the light emitting group and the connection group. The spacer may increase the number of light emitting groups attached to the core / shell structure, and may facilitate dispersion of a ligand including a light emitting material in a solvent during the manufacture of the light emitting quantum dots. Specifically, the spacer can be used substituted or unsubstituted, saturated or unsaturated _C 1 _{-C 30} alkyl _groups, cycloalkyl groups C 3 _{-C 40,} the silane Si 1 _{-Si 30,} which It is not limited to.

In the light emitting quantum dot of the present invention, the ligand includes a light emitting group that is color-converted by pH change. As a specific example, the ligand is one of those represented by the following chemical formulas 1 to 13. Also good.
[Chemical Formula 1]

[Chemical formula 2]

[Chemical formula 3]

[Chemical formula 4]

[Chemical formula 5]

[Chemical formula 6]

[Chemical formula 7]

[Chemical formula 8]

[Chemical formula 9]

[Chemical formula 10]

[Chemical formula 11]

[Chemical formula 12]

[Chemical formula 13]

In the above chemical formula, the moiety bonded to the core / shell structure is a —O— moiety of a sulfo group or a carboxyl group, and Alkyl, R ₁ and R ₂ are each independently substituted or unsubstituted saturated or unsubstituted. It means an alkyl of saturated _C 1 _{-C 30.}

  In the present invention, the size of the entire light-emitting quantum dot including a light-emitting group whose color is converted by a change in pH at the end can be arbitrarily adjusted, and is preferably 5 to 30 nm, more preferably 10 to 20 nm. . In the present invention, the emission intensity of the core / shell structure and the light emitting group can be arbitrarily adjusted. Preferably, in the present invention, when the core / shell structure and the light emitting group are in a complementary color relationship, the core / shell structure The difference in the emission intensity ratio between the body and the emission group is preferably within 30%. For example, when the emission intensity of the region band of 400 to 500 nm is 1, the emission intensity of the region band of 500 to 800 nm is preferably 0.7 to 1.3, and the emission intensity of the region band of 500 to 800 nm is preferably When it is 1, the emission intensity in the region of 400 to 500 nm is preferably 0.7 to 1.3.

  FIG. 1 shows the color change of the luminescent group of the present invention using the ligand of Formula 1, and FIG. 2 shows the PL spectrum of the ligand of Formula 1.

  As shown in FIG. 1 and FIG. 2, the emission color of the light emitting group changes according to the change in pH, and emits a blue color at a low pH, and emits a green color at a high pH. To do.

  FIG. 3 shows that the quantum dot using the ligand of Formula 1 or 2 can achieve white light emission through pH adjustment.

  As shown in FIG. 3, the quantum dots of the present invention can emit white light with high purity by adjusting pH through a buffer solution.

  In addition, the quantum dots according to the present invention can be obtained by adjusting the emission group to be color-converted by the change in the color and pH of the core / shell structure, as shown in FIGS. White light emission (FIG. 4), white light emission (FIG. 5) with a color purity close to that of a standard light source while moving to a blue-green wavelength, and RGB white light emission (FIG. 6) are also possible.

  The luminescent quantum dot according to the present invention may be manufactured by adding a ligand including a luminescent group that is color-converted by a change in pH to a solution in which a core / shell structure is dispersed, and then stirring. In the above, the core / shell structure can be manufactured by a known method, or by a synthesis method shown in FIG.

In addition, a ligand including a luminescent group can be manufactured by combining a linking group with a luminescent group or by adding a spacer between the luminescent group and the linking group. It can be manufactured through the processes of Equations 1 and 2.
[Reaction Formula 1]

[Reaction Formula 2]

[Reaction Formula 3]

  In the method of attaching a ligand containing a light emitting group to a core / shell structure, the stirring may be performed at a temperature of room temperature to 100 ° C. for 0.1 to 100 hours.

  Moreover, this invention provides the light emitting element (QLED) using the said light emission quantum dot, and its manufacturing method. In the present invention, it is needless to say that other known techniques can be applied to the light emitting element except for a light emitting layer formed using the light emitting quantum dots according to the present invention.

  As an example, according to one embodiment, the light emitting device may be configured such that a substrate, a cathode, a light emitting layer formed of light emitting quantum dots according to the present invention, and an anode are sequentially formed. In addition, an electron transport layer can be further formed between them, and a hole transport layer can be further formed between the light emitting layer and the anode. Further, if necessary, a hole suppression layer can be further included between the electron transport layer and the light emitting layer, and a buffer layer can be formed between the layers.

  In the present invention, a light emitting device (QLED) using light emitting quantum dots can be formed by a normal manufacturing method, and each organic film including the light emitting layer can be manufactured to have a thickness of 30 to 100 nm. it can.

  When used as a light-emitting layer using a light-emitting quantum dot according to the present invention, for example, in the organic electroluminescent device, a buffer layer can be formed between each layer, and such a buffer layer is usually used as a material. For example, copper phthalocyanine, polythiophene, polyaniline, polyacetylene, polypyrrole, ne, or polyphenylene vinyl. However, the present invention is not limited to this.

  As the material of the hole transport layer, a commonly used material can be used, and for example, polytriphenylamine can be used, but is not limited thereto.

  As the material for the electron transport layer, a commonly used material can be used. For example, polyoxadiazole can be used, but the material is not limited thereto.

As the material for the hole suppression layer, a commonly used substance can be used. For example, LiF, BaF ₂ or MgF ₂ can be used, but the material is not limited thereto.

  More specifically, the light emitting device of the present invention can be manufactured by the method described in FIG.

  The light emitting device according to the present invention manufactured as described above has high stability, and has excellent color purity and high light emission efficiency as compared with conventional light emitting devices.

  Hereinafter, preferred examples will be presented for the understanding of the present invention. However, the following examples are merely illustrative of the present invention, and the scope of the present invention is not limited to the following examples.

[Synthesis Example 1]
3,6,8-Tribromopyrene-1-ol Under argon or nitrogen atmosphere, put 250 g of pyren-1-ol, 17.49 g of bromine, and 200 ml of nitrobenzene in a 250 ml round bottom flask and reflux for 14 hours. Stir with heating. After the reaction, it was cooled to room temperature and the precipitated crystals were separated by filtration. This was recrystallized with toluene to obtain 11 g of crystals.

[Synthesis Example 2]
3,6,8-Tri (2-bromoethyl) pyrene-1-ol 10 g of 3,6,8-tribromopyrene-1-ol was dissolved in 300 ml of anhydrous diethyl ether. Here, 50 ml of n-BuLi (2M) was gradually added at 0 ° C. After maintaining at 0 ° C. for 1 hour, 1.10-dibromoethyl (14 g) was added, and after 30 minutes, the mixture was stirred at reflux for 4 hours. If the reaction was not carried out any further, 80 ml of distilled water was added after cooling to room temperature. The organic layer was collected and the aqueous layer was extracted 3 times with 40 ml of ethyl ether. After removing water with anhydrous magnesium sulfate, column separation was performed using hexane as a mobile phase to obtain 5.5 g of 3,6,8-tri (2-bromoethyl) pyrene-1-ol.

[Synthesis Example 3]
8- (hydroxypyrene-1,3,6-triyl) triethanesulfonic acid 3,6,8-tri (2-bromoethyl) pyrene-1-ol 5.3 g and an excess amount of sodium sulfite It was dissolved in 30 ml of distilled water and stirred at reflux for 16 hours. The mixture was cooled to room temperature and extracted into diethyl ether and distilled water to obtain 4.1 g of 8- (hydroxypyrene-1,3,6-triyl) triethanesulfonic acid.

[Synthesis Example 4]
CdSe / ZnS synthesis (quantum dot synthesis)
For the synthesis of CdSe quantum dots, 0.4 mmol of cadmium oxide, 4 mmol of zinc acetate, and 17.6 mmol of oleic acid were placed in a three-neck flask and heated at a temperature of 150 ° C. in an Ar gas atmosphere. OA-Cd complex (OA-Cd complex) and OA-Zn acetate complex (OA-Zn acetate complex) were produced. And 20 ml of 1-octadequin was added here, and the mixture was heated at a temperature of 300 ° C. in an Ar gas atmosphere. Thereafter, a Se solution was rapidly injected into the reaction vessel. The Se solution was prepared by mixing 0.4 mmol of Se powder and 4 mmol of sulfur powder in 3 ml of n-trioctylphosphine. After injecting a Se solution, it was reacted at 300 ° C. for 10 minutes for crystal growth of quantum dots, and then rapidly cooled to room temperature. Thereafter, an excessive amount of methanol was added, and after passing through a centrifugal separation process, orange quantum dots were produced.

Example 1
A CdSe / ZnS solution (0.2 ml, 5 mg / ml in hexane) is produced from the quantum dots produced in Synthesis Example 4, and a luminescent material represented by Chemical Formula 1 (0.5 ml, 3 mM in DMSO) is added. Stir for a minute at room temperature. After sufficient methanol was added to the reaction flask to solidify it, it was centrifuged to produce white quantum dots.

Example 2
A CdSe / ZnS solution (0.2 ml, 5 mg / ml in hexane) is produced from the quantum dots produced in Synthesis Example 4, and a luminescent material (0.5 ml, 3 mM in DMSO) represented by Chemical Formula 1 is added. After adding 0.05 ml of 2 wt% NaOH buffer solution, the mixture was stirred at room temperature for 30 minutes. After sufficient methanol was added to the reaction flask to solidify it, it was centrifuged to produce white quantum dots.

Example 3
A CdSe / ZnS solution (0.2 ml, 5 mg / ml in hexane) is produced from the quantum dots produced in Synthesis Example 4, and a luminescent material (0.5 ml, 3 mM in DMSO) represented by Chemical Formula 1 is added. After adding 0.2 ml of 2 wt% NaOH buffer solution, the mixture was stirred at room temperature for 30 minutes. After sufficient methanol was added to the reaction flask to solidify it, it was centrifuged to produce white quantum dots.

Example 4
A CdSe / ZnS solution (0.2 ml, 5 mg / ml in hexane) is produced from the quantum dots produced in Synthesis Example 4, and the luminescent material (0.5 ml, 3 mM in DMSO) produced in Synthesis Example 3 is added. For 30 minutes at room temperature. After sufficient methanol was added to the reaction flask to solidify it, it was centrifuged to produce white quantum dots.

Example 5
A CdSe / ZnS solution (0.2 ml, 5 mg / ml in hexane) is produced from the quantum dots produced in Synthesis Example 4, and the luminescent material (0.5 ml, 3 mM in DMSO) produced in Synthesis Example 3 is added. After adding 0.1 ml of 0.2 wt% NaOH buffer solution, the mixture was stirred at room temperature for 30 minutes. After sufficient methanol was added to the reaction flask to solidify it, it was centrifuged to produce white quantum dots.

Example 6 Production of Device Using White Quantum Dots A glass substrate coated with a thin film of indium tin oxide (ITO) with a thickness of 1500 mm was washed with distilled water ultrasonic waves. When the distilled water cleaning is completed, the substrate is ultrasonically cleaned with a solvent such as isopropyl alcohol, acetone, methanol, etc., dried, transferred to a plasma cleaner, and the substrate is cleaned with oxygen plasma for 5 minutes. A PEDOT: PSS / IPA 9: 1 weight ratio was spin-coated at 4000 rpm for 30 seconds as a hole injection layer on the substrate to form a film. Next, PVK was dissolved in chlorobenzene to prepare a 1 wt% solution, and spin-coated at 3000 rpm for 60 seconds to form a hole transport layer. Next, the white quantum dots synthesized in Example 1 were spin-coated at 2000 rpm for 30 seconds to form a light emitting layer. A quantum dot light emitting device was manufactured by depositing Al at 100 nm as a cathode and sealing the device with a glove box. A white (cool-white) emission of color coordinates (0.31 0.35) could be confirmed. FIG. 9 shows an EL spectrum of the light emitting device manufactured according to Example 6.

Further, the current density-voltage-luminance (IV-L) characteristics of the quantum dot light-emitting elements were measured with a Keithley-236 source-measurement unit (FIG. 10). In the case of this element, the luminance was 3400 cd / m ² , the luminance ratio was 1.2 cd / A, and the driving voltage was 2 V, and white light emission with color coordinates (0.34 0.36) could be confirmed.

Examples 7 to 8 Production of device using white quantum dots The light emitting device was produced using the quantum dots produced in Examples 2 to 3 instead of the quantum dots produced in Example 1 in Example 6 above. Except for the above, a light emitting device was manufactured by the same method as in Example 6. In the case of this element, it is possible to confirm the white (warm-white) emission of the color coordinates (0.35 0.39) and (0.36, 0.42), and confirm the color purity change due to pH adjustment. I was able to.

Example 9 Production of Device Using White Quantum Dots A glass substrate coated with a thin film of indium tin oxide (ITO) with a thickness of 1500 mm was washed with distilled water ultrasonic waves. When the distilled water cleaning is completed, the substrate is ultrasonically cleaned with a solvent such as isopropyl alcohol, acetone, methanol, etc., dried, transferred to a plasma cleaner, and the substrate is cleaned with oxygen plasma for 5 minutes. A PEDOT: PSS / IPA 9: 1 weight ratio was spin-coated at 4000 rpm for 30 seconds as a hole injection layer on the substrate to form a film. Next, PVK was dissolved in chlorobenzene to prepare a 1 wt% solution, and spin-coated at 3000 rpm for 60 seconds to form a hole transport layer. Next, the white quantum dots synthesized in Example 4 were spin-coated at 2000 rpm for 30 seconds to form a light emitting layer. A quantum dot light emitting device was manufactured by depositing Al at 100 nm as a cathode and sealing the device with a glove box. A white (white-white) emission of color coordinates (0.36 0.37) could be confirmed.

Further, the current density-voltage-luminance (IV-L) characteristics of the quantum dot light-emitting elements were measured with a Keithley-236 source-measurement unit (FIG. 10). In the case of this element, luminance was 2100 cd / m ² at 6 V, and white light emission could be confirmed.

Example 10 Production of Device Using White Quantum Dots Except that the light emitting device was produced using the quantum dots produced in Example 5 instead of the quantum dots produced in Example 4 in Example 9. A light emitting device was manufactured in the same manner as in Example 8. In the case of this element, white light emission could be confirmed, and a change in color purity due to pH adjustment could be confirmed.

  The light-emitting quantum dot according to the present invention has excellent dispersibility and stability on an aqueous solution and can emit white light by itself without a separate filter layer. Therefore, the structure is simple when applied to a light-emitting device. And is excellent in color purity and light emission characteristics, and thus can have excellent color purity, high stability, and high light emission efficiency as compared with a conventional light emitting element.

Claims (11)

A quantum dot comprising a core / shell structure and a ligand attached to the surface of the shell, comprising:
A light emitting group in which the ligand is color-converted by pH change, a connecting group connecting the shell and the light emitting group, and a spacer between the connecting group and the light emitting group,
The linking group is selected from the group consisting of a sulfo group, a thiol group, a carboxy group, an amine group, a phospine group, and a phosphide group,
The spacer is a substituted or unsubstituted, saturated or unsaturated _C 1 _{-C 30} alkyl _groups, cycloalkyl groups C 3 _{-C 40,} a silane of the Si 1 _{-Si 30,} the quantum dots. The light emitting quantum dot according to claim 1 , wherein the light emitting group emits light in a band of 400 to 800 nm. The light emitting quantum dot according to claim 1 , wherein the ligand is represented by any one of the following chemical formulas 2 to 13.
[Chemical formula 2]

[Chemical formula 3]

[Chemical formula 4]

[Chemical formula 5]

[Chemical formula 6]

[Chemical formula 7]

[Chemical formula 8]

[Chemical formula 9]

[Chemical formula 10]

[Chemical formula 11]

[Chemical formula 12]

[Chemical formula 13]
In the above chemical formula, the moiety bonded to the core / shell structure is a —O— moiety of a sulfo group or a carboxyl group, and Alkyl, R ₁ and R ₂ are each independently substituted or unsubstituted saturated or unsaturated. It means an alkyl of C ₁ -C _30. The light emitting quantum dot according to claim 1, wherein a particle diameter of the quantum dot is 5 to 30 nm. The light emitting quantum dot according to claim 1, wherein the quantum dot emits white light. 2. The light emitting quantum dot according to claim 1, wherein the difference in emission intensity ratio between the core / shell structure and the light emitting group is within 30%. The method for producing a light-emitting quantum dot according to claim 1, further comprising the step of adding a ligand containing a light-emitting group whose color is changed by pH change to a solution in which a core / shell structure is dispersed, and then stirring the mixture. . The method of manufacturing a light-emitting quantum dot according to claim 7 , wherein the stirring is performed at a temperature of room temperature to 100 ° C for 0.1 to 100 hours. In the light emitting element,
A light emitting device comprising the light emitting quantum dot according to claim 1 as a light emitting substance. In the method for manufacturing a light emitting device,
A method for manufacturing a light emitting device, comprising the step of forming a light emitting layer with the light emitting quantum dots according to claim 1. The method for producing a light emitting device according to claim 10 , comprising a step of adjusting an emission wavelength and color purity by adding an acid and a base buffer solution before forming a light emitting layer with the light emitting quantum dots according to claim 1.