KR101734465B1 - White electroluminescent lighting device based on a single quantum dot emitter and method for fabricating the same - Google Patents

Abstract

Disclosed are a white quantum dot (QD) light-emitting device capable of emitting white light by using a single kind thereof and using quantum dots of which a spectrum can be adjusted to ensure various color temperatures, and a method for producing the same. The white quantum dot light-emitting device according to the present invention comprises: a pore transfer layer; a quantum dot light-emitting layer; and an electron transfer layer. Quantum dots of the quantum dot light-emitting layer are white quantum dots having I-III-VI-based ternary system Cu-Ga-S or Ag-Ga-S or I-III-VI-based quaternary system X-In-Ga-S or Zn-X-Ga-S (X=Cu, Ag) core quantum dots and ZnS shells. According to the present invention, a white EL device having a high color rendering index of 83-88, brilliance of 1007 cd/m^2, electrical current efficiency of 3.6 cd/A, power efficiency of 1.9 lm/W, and EQE of 1.9% can be ensured, and a bendable white plate QLED can also be produced.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a white electroluminescent device including a single quantum dot emitter and a method of fabricating the same.

The present invention relates to an electroluminescence (EL) device using a quantum dot (QD), and more particularly, to a QD-light emitting device and a method of manufacturing the same, And a manufacturing method thereof.

In recent decades, QD-light emitting devices (hereinafter collectively referred to as QLEDs), such as colloidal QD EL devices or light emitting diodes (QLEDs), have been developed through QD core / shell composition and structure modification, charge transport layer development, Much research has been done.

The QLED generally has a multilayer structure including a hole transport layer (HTL), a QD light emitting layer (EML), and an electron transport layer (ETL). A dramatic improvement in QLED performance was achieved by introducing a hybrid charge transport layer (CTL) consisting of organic HTL and inorganic ETL. It has been reported that through these hybrid CTL and Cd-based II-VI quantum dots, external quantum efficiency (EQE) of 10.7, 14.5 and ~ 20% was achieved for blue, green and red QLED, respectively.

In addition to such monochromatic QLEDs, studies on multi-colored white devices have also been conducted in light of practical applications such as general illumination and displays.

White EL can be simply implemented by a combination of quantum dot emission and secondary parasitic luminescence from peripheral organic CTL, but these devices typically have very low EQE. Methods for forming multi-layer EMLs or forming mixed EMLs using quantum dots with different colors have also been proposed. However, in order to obtain a balanced white EL from various quantum dots constituting the EML, it is necessary to optimize the stacking order and thickness of the multilayer EML, the quantum dot content ratio of the mixed EML, and this is very complicated. In addition, in the mixed EML, undesirable spectral variations occur depending on the bias, and color stability is deteriorated.

Considering these points, if a single kind of quantum dot that emits white light by emitting all the visible light region can be used, the color stability of the white element can be ensured and the manufacturing method is not complicated.

In order to obtain a broad spectrum of the visible light region from a single quantum dot, it is possible to dope the quantum dot with an impurity ion such as Mn ^{2 +} or Cu ⁺ ions. However, the results reported so far using this method show that white light emission is insufficient due to lack of spectrum.

Another way to obtain white luminescence from a single quantum dot is to use radioactive recombination in a defect-related internal gap state. For example, the Rosenthal group reported white luminescence in CdSe quantum dots with a size of 2 nm or less [M. J. Bowers, J. R. McBride, S. J. Rosenthal, J. Am. Chem. Soc. 2005, 127, 15378]. However, such a quantum dot not only has a problem of toxicity because it contains Cd but also has a quantum efficiency of less than 10%, and thus has limitations in application to devices such as LEDs.

Accordingly, there is a demand for a technique of manufacturing a white light emitting device using a single quantum dot with a high quantum efficiency while using non-Cd-based quantum dots.

Disclosure of Invention Technical Problem [6] The present invention provides a purple white quantum dot light-emitting device capable of emitting white light using a single kind of quantum dot, and a method of manufacturing the same.

In order to solve the above problems, the white quantum dot light-emitting device according to the present invention includes a hole transport layer, a quantum dot luminescent layer, and an electron transport layer, and the quantum dots of the quantum dot luminescent layer include an I-III-VI system ternary Cu- Ag-Ga-S, or I-III-VI quaternary component X-In-Ga-S or Zn-X-Ga-S (X = Cu, Ag) core quantum dots and a ZnS shell.

In this case, it is preferable that Cu: Ga or Ag: Ga in the ternary system or X: (In + Ga) or X: (Zn + Ga) in the quartz component is 1:10 to 1: 1.

In the case of the four-component system X-In-Ga-S, In: Ga = (1-x): x or Zn: Ga = 0.5 < x < 1.

Here, the core quantum dots may be doped with an impurity such as Mn. In the case of Mn-doped ternary quantum dots, the molar ratio of Mn: Cu or Mn: Ag may be more than 0 and 0.5 or less, and in the case of Mn-doped tetragonal quantum dots, the Mn: X molar ratio may be more than 0 and 0.5 or less.

The white quantum dot light emitting device according to the present invention further comprises a cathode, a hole injecting layer and a cathode, wherein the hole injecting layer is made of poly (ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS), the hole transporting layer is made of poly (9-vinlycarbazole) (PVK).

The hole transport layer may be an organic material or an inorganic material, and the electron transport layer may include ZnO nanoparticles (NP).

The method of manufacturing such a white quantum dot-emitting device and the method of manufacturing the quantum dot used herein can be all-solution processing because it can be performed by a solution method, that is, a solvent-based method.

The method for manufacturing a white quantum dot light-emitting device according to the present invention includes the steps of forming a hole transport layer, a quantum dot luminescent layer, and an electron transport layer, wherein the step of forming the quantum dot light emitting layer comprises: Cu-Ga-S or Ag-Ga-S or I-III-VI quaternary component X-In-Ga-S or Zn-X-Ga-S (X = Cu, Ag) core quantum dots and ZnS shell Coating and baking a solution in which white quantum dots are dispersed.

For example, the method for producing the quantum dots described above is a method of manufacturing a quantum dot of I-III-VI system ternary Cu-Ga-S or Ag-Ga-S or I- Or Zn-X-Ga-S (X = Cu, Ag) core quantum dots; Selectively adsorbing Mn on the core quantum dot surface; And forming a ZnS shell on the core quantum dots. When Mn is adsorbed on the surface of the core quantum dots, Mn is diffused into the core quantum dots during formation of the ZnS shell.

The step of forming the core quantum dots may be performed by mixing and heating the precursor and the solvent.

The step of adsorbing Mn may be carried out by applying an Mn dopant stock solution.

The Mn dopant stock solution may comprise a Mn precursor, octadecene and oleic acid.

The step of forming the ZnS shell may be performed by applying a ZnS stock solution.

The step of forming the ZnS shell is preferably performed two or more times in succession.

At this time, the concentration and the reaction temperature and time of each ZnS stock solution may be different.

In a preferred embodiment, the step of forming the core quantum dots is performed by injecting a sulfur source into a copper precursor, a gallium precursor, a sulfur precursor and a solvent mixture solution, and the step of forming the ZnS shell comprises: Applying a solution; And applying a second ZnS stock solution to the mixed solution, wherein the ZnS stock solutions comprise a Zn precursor, a sulfur precursor and octadecene, wherein the first ZnS stock solution comprises oleic acid, stearic acid, and myristic acid As shown in FIG.

In accordance with the present invention, the I-III-VI system ternary Cu-Ga-S or Ag-Ga-S or I-III-VI system component system X-In-Ga-S or Zn- = Cu, Ag) core quantum dots and ZnS shells, white light emission can be realized by realizing a very wide emission spectrum from blue to red region by single type quantum dots.

An example of realizing white light emission using a single kind of quantum dot in a non-Cd-system is not yet known. In the case of using a single kind of quantum dot, since the number of variables to be controlled is reduced as compared with the case of using various kinds of quantum dots, there is an advantage that a device with good reproducibility can be manufactured.

In addition, since the present invention utilizes quantum dots having enhancement efficiency characteristics through effective ZnS shell passivation, the device characteristics are excellent.

Furthermore, in the present invention, it is also possible to adjust the white emission spectrum or to adjust the ZnS shelling time by doping Mn with the basic I-III-VI system composition. Adjusting the Mn concentration or ZnS shelling time can systematically adjust the spectra from cool white to warm white while maintaining PL (Photoluminescence) quantum efficiency.

Using such a quantum dot, a white EL device having a high color rendering index (83-88), a luminance of 1007 cd / m ² , a current efficiency of 3.6 cd / A, a power efficiency of 1.9 lm / W, and a 1.9% EQE can be realized, White flat panel QLEDs can also be manufactured.

1 is a schematic cross-sectional view of a white quantum dot-emitting device according to the present invention.
2 is a schematic view of a quantum dot included in a white quantum dot-emitting device according to the present invention.
FIG. 3 is a flowchart showing an embodiment of a method for manufacturing quantum dots included in a white quantum dot-emitting device according to the present invention.
4 is an EDS spectrum of CGS / ZnS quantum dots (samples 1 to 4) prepared by varying the molar ratio of Cu / Ga precursor to 1/1, 1/2, 1/4 and 1/8 according to the experimental example of the present invention .
Fig. 5 (a) shows the absorption spectrum and bandgap variation of samples 1 to 4 according to the experimental example of the present invention, (b) shows the normalized PL spectrum and fluorescence image, (c) It is a PL change graph expressed as a function of time.
Fig. 6 shows the results of calculating the optical bandgaps of Samples 1 to 4 using the ( Ahν ) ² - hν relation ( A = absorption, h = Planck's constant, v = optical frequency).
Figure 7 (a) (B) is a low magnification TEM image of Sample 4, and (c) is a high magnification TEM photograph of Sample 4. Fig.
FIG. 8 is a graph showing PL spectra of Samples 1 to 4 according to the experimental example of the present invention by Gaussian function fitting method.
9 (a) is a graph of PL QY variation of samples 1 to 4 according to the experimental example of the present invention, (b) is PL QY expressed as a function of second shelling time in sample 4, And the UV-vis spectral change expressed as a function of the second shelling time.
10 (a) shows a white QLED structure including a single quantum dot emitter manufactured according to the experimental example of the present invention, (b) is a cross-sectional TEM image of an actual device, (c) is a band diagram, (d) shows the white light emission of the device manufactured on the glass, and (e) shows the white light emission of the device manufactured on the PEN substrate.
11 is a PESA measurement result of Sample 4 according to the experimental example of the present invention.
FIG. 12A shows the collected EL spectrum, FIG. 12B shows the EL spectrum normalized to the HE EL wavelength, and FIG. 12C shows the CIE color coordinates of the white EL as a function of the applied voltage.
Figure 13 shows the PL decay of CGS / ZnS quantum dots at 475 nm (CB-to-V _Cu For light emission) and 575 nm (for DAP).
14 (a) is a current density-luminance variation according to a voltage in a white QLED, (b) is a current efficiency-EQE-power efficiency variation, and (c) is a graph of CRI-CCT variation.
FIG. 15 shows the results of the white QLED using the CGS / ZnS quantum dot for the second ZnS-Schering ring for 20 minutes, wherein (a) is the EL spectrum and (b) is the CIE color coordinate corresponding thereto.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. It is provided to let you know.

1 is a schematic cross-sectional view illustrating a QLED as a white quantum dot-emitting device according to the present invention.

1, the QLED 1 includes a hole transport layer 40 (HTL), a quantum dot (QD) emission layer 70 (EML), and an electron transport layer 80 (ETL). The QD light emitting layer 70 is a layer that emits light by coupling holes and electrons entered from the hole transporting layer 40 and the electron transporting layer 80, respectively. This multilayer structure can be formed on the substrate 10 serving as a mechanical support and includes a cathode 20 for anode injection and a cathode 90 for injecting electrons, And a hole injection layer (HIL) 30 may be further formed between the anode 40 and the hole injection layer 30.

The substrate 10 may be a transparent or flat glass substrate or a transparent plastic substrate. The substrate 10 may be used after being ultrasonically cleaned with a solvent such as isopropyl alcohol, acetone, or methanol, and subjected to UV-ozone treatment, in order to remove contaminants. It is possible to manufacture a flat white device which can be bent when a transparent plastic substrate is used.

The anode 20 and the cathode 90 are made of a metal oxide corresponding to each transparent / opaque condition, including metals, and other non-oxides. The cathode 20 may be made of a transparent conductive metal such as ITO, IZO, ITZO, or AZO, and the cathode 90 may be made of a metal having a small work function such as Ca, Ba, Ca / Al, LiF / Ca, LiF / Al, BaF ₂ / Al, BaF ₂ / Ca / Al, Al, Mg, and Ag: Mg alloys.

The hole injection layer 30 and the hole transport layer 40 facilitate injection of holes from the anode 20 and transfer holes to the QD light emitting layer 70. The hole transport layer 40 may be an organic material or an inorganic material. In the organic material, CBP (4,

N'-diphenyl-N, N'-bis (1 = naphtyl) -1,1'-biphenyl-4,4'-diamine ),

(4,4 ', 4 "-tris (N-carbazolyl) -triphenylamine) or DNTPD (N, N'-

N.N'-diphenylbenzidine), and in the case of an inorganic material, it may be composed of an oxide of NiO or MoO ₃ . According to a preferred embodiment, the hole transport layer 40 is an organic material. In one specific example, the hole injection layer 30 is poly (ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS), and the hole transport layer 40 is poly (9-vinlycarbazole) (PVK).

The QD light emitting layer 70 includes quantum dots specific to the present invention. The QD light emitting layer 70 can be formed by a solution process in which a dispersion containing a quantum dot is coated on a solvent. The coating method may be carried out, for example, by drop casting, spin coating or spin casting, dip coating, spray coating, flow coating, Screen printing or inkjet printing may be used alone or in combination.

The quantum dots used herein can be synthesized by a wet process in which the precursor material is introduced into an organic solvent and the particles are grown. Depending on the degree of particle growth, various wavelengths of light can be obtained by controlling the energy bandgap. This quantum dot will be described in more detail below.

The electron transport layer 80 facilitates injection of electrons from the cathode 90 and transmits electrons to the QD emission layer 70. The electron transport layer 80 may include ZnO nanoparticles. For example, the electron transport layer 80 may be formed by coating a dispersion containing ZnO nanoparticles in a solvent on a QD emission layer 70 by a solution process, and then volatilizing the solvent.

2 is a schematic view of quantum dots included in a white quantum dot-emitting device according to the present invention.

Referring to FIG. 2, the present invention proposes to use a single kind of non-Cd-based quantum dot 100 for white light emission. The quantum dot 100 is formed of an I-III-VI system ternary Cu-Ga-S or Ag-Ga-S or I-III-VI system X-In-Ga-S or Zn- (X = Cu, Ag) core quantum dots 120 and ZnS shells 130.

The core quantum dot 120 is an I-III-VI system ternary or quadrature system, and Mn may be further doped. When the core quantum dots 120 and the ZnS shell 130 are formed, PL and quantum efficiency are improved.

The present inventors must include Cu or Ag and Ga and S for the I-III-VI quantum dot to emit white light in a single composition. That is, Cu-Ga-S (CGS) or Ag- And particularly the chemical composition should be adjusted so that the ratio of Cu or Ag and Ga is 1:10 to 1: 1 and Cu or Ag is the same amount or slightly lacking as Ga. When the ratio of Cu or Ag and Ga is 1/10 or more, white light emission is seen by the combination of spectra, and when the ratio is larger than 1, white light emission does not occur.

On the other hand, four-component X-In-Ga-S or Zn-X-Ga-S (X = Cu, Ag) can be formed by alloying In or Zn with the basic ternary composition of CGS or Ag- .

As in the ternary system, it is preferable that X: (In + Ga) or X: (Zn + Ga) is 1:10 to 1: 1. Particularly, it is preferable that In: Ga = (1-x): x in the quaternary component X-In-Ga-S or Zn: Ga = (1-x): x in the quaternary component Zn-X- 0.5 < x < 1. The adjustment of the composition ratio between Ga and In or Zn which can partially substitute Ga is performed to control the wavelength characteristic. However, the composition ratio of Ga, In, or Zn is controlled while adjusting the ratio of Cu or Ag and Ga. Is a peculiar matter of the present invention. Under these composition conditions, the quaternary core quantum dot can realize a very broad emission spectrum from blue to red region.

The core quantum dot 120 includes various defects therein, and a wide emission band can be obtained because various light emission is performed through the defect. Various emission wavelengths can be controlled by controlling the composition of the core quantum dot 120.

Through the basic composition of the I-III-VI system, the quantum dot 100 according to the present invention has a white emission spectrum. When Mn is doped into the basic composition of I-III-VI system, the color temperature can be adjusted even within the white emission spectrum, and the color temperature can be further controlled from cool white to warm white. The Mn: Cu or Mn: Ag molar ratio in the case of a ternary quantum dot may be more than 0 and 0.5 or less in the case of doping with Mn, and the Mn: X molar ratio in the case of a quaternary quantum dot with Mn doping may be 0 or more and 0.5 or less. If such molar ratio exceeds 0, Mn is doped. When the molar ratio is larger than 0.5, the secondary phase may occur or the color temperature change may be insignificant.

In general, doping a dopant in a quantum dot as a substitutional or interstitial type is quite tricky because the quantum dot lattice tends to emit a dopant. Therefore, attempts to simultaneously dopant the dopant while synthesizing the quantum dots simply do not produce good results. In the present invention, a method of diffusing Mn into the core quantum dot 120 during surface adsorption of Mn after forming the core quantum dot 120 once and forming ZnS shell 130 later is also proposed.

The ZnS shell 130 may be formed in a double-layer structure. That is, as shown in the figure, the ZnS shell may be formed up to the portion indicated by the dotted line, and then the remaining ZnS shell may be formed to the portion indicated by the solid line. In particular, since the ZnS shell forming process is performed continuously as described below, the layer discrimination in the ZnS shell 130 may be virtually absent. Each layer may have a different composition. The composition at this time may be discontinuously changed on the basis of a dotted line or may be continuously changed over the entire ZnS shell 130. This double ZnS shell 130 has excellent passivation effect. The quantum efficiency of the quantum dot 100 can be improved.

As described above, according to the present invention, the I-III-VI system ternary Cu-Ga-S or Ag-Ga-S or I- It is possible to realize a very wide emission spectrum from the blue region to the red region by using the quantum dot 100 having the S (X = Cu, Ag) core quantum dot 120 and the ZnS shell 130. Accordingly, it is possible to realize white light emission in the EL element even by using one type, that is, a single quantum dot. The quantum dot 100 may have a high quantum efficiency.

Furthermore, in the present invention, the doping of Mn makes it possible to control the color temperature in the white light emission spectrum. By adjusting the Mn concentration, the spectrum can be systematically adjusted from cool white to warm white while maintaining the PL quantum efficiency. In addition, the ZnS shelling time can be adjusted to achieve the desired color temperature from cool white to warm white.

An example of realizing white light emission using a single kind of non-Cd-based quantum dot as in the present invention is not yet known. In the case of using a single kind of quantum dot, since the number of variables to be controlled is reduced as compared with the case of using various kinds of quantum dots, there is an advantage that a device with good reproducibility can be manufactured.

On the other hand, the core quantum dot 120 can be fabricated through a hot colloid method, a solvothermal method, or heating-up or hot-injection, and the ZnS shell 130 ) Can also be carried out by a cation exchange process, a solvent heating method and the like. Hereinafter, preferred embodiments of the production method will be described.

FIG. 3 is a flowchart showing an embodiment of a method for manufacturing quantum dots included in a white quantum dot-emitting device according to the present invention. In this embodiment, the case of forming the CGS core quantum dot is taken as an example, but the case of forming the core quantum dots of other kinds will be easily understood from the following description.

First, the core quantum dots 120, preferably the CGS core quantum dots are formed by mixing and heating the precursor and the solvent (step S100 in Fig. 3). To grow full-scale quantum dots, a sulfur source can be injected into a mixed solution of a precursor and a solvent. The reaction temperature for forming the core quantum dot 120 may range from 120 to 350 DEG C, and the reaction time may range from 1 second to 60 minutes.

The starting material for growing the core quantum dot 120 is a combination of copper iodide as a copper precursor, gallium iodide as a gallium precursor, 1-dodecanethiol as a sulfur precursor, and oleylamine as a solvent . The sulfur source injected for full-scale CGS core formation is sulfur and can be of the octadecene type.

The ratio of the starting materials is set in the range of Cu: Ga = 1: 10 to 1: 1 as mentioned above. For example, when 0.5 mmol of Ga precursor is used, the amount of 1-dodecanethiol that can be applied at this time is 0 to 10 mL, the amount of oleylamine is 1 to 50 mL, and the amount of sulfur is 0.1 to 10 mmol.

In the case of the copper precursor, in addition to copper iodide, copper acetate, copper bromide, copper chloride and the like may be used. In the case of the gallium precursor, in addition to gallium iodide, gallium acetate, gallium chloride, gallium acetylacetonate and the like may be used. In the case of the sulfur precursor, various alkylthiol-based compounds such as octanethiol, hexadecanethiol, decanethiol, etc. may be used in addition to 1-dodecanethiol. In the case of a solvent, various fatty amines such as dodecylamine, trioctylamine and the like may be used in addition to oleylamine.

Then, Mn is adsorbed on the surface of the core quantum dot 120 (step S110 in FIG. 3). This step is an optional step because it is performed only when it is desired to dope Mn.

This step can be performed by applying an Mn dopant stock solution. For example, the Mn dopant stock solution may be prepared by dissolving an Mn precursor such as manganese acetate in octadecene and oleic acid.

The ZnS stock solution is then applied to the core quantum dots 120 to form a ZnS shell 130 (step S120 in FIG. 3). If step S110 of FIG. 3 is performed, the Mn adsorbed on the surface diffuses into the core quantum dot 120 at step S120.

Not all of the Mn adsorbed on the surface diffuses into the core quantum dots 120 but a large amount is removed in the process of applying the ZnS stock solution. Thus, it is necessary to prepare the Mn dopant stock solution at a concentration higher than the target Mn concentration in the final product.

The step of forming the ZnS shell 130 may be performed two or more times in succession. At this time, the concentration and the reaction temperature and time of the ZnS stock solution in each step may be different. The temperature of the second reaction may be higher or longer.

For example, a ZnS stock solution is first applied to the core quantum dot 120 to form a ZnS shell first, and then another ZnS stock solution is applied to the resultant to form a ZnS shell secondarily.

The first ZnS stock solution in step S120 can be prepared by using zinc acetate as the Zn precursor, 1-dodecanethiol as the sulfur precursor, and octadecene and oleic acid as the solvent. In this case, zinc stearate, zinc oxide, zinc nitride, zinc acetylacetonate, and the like may be used in addition to zinc acetate in the case of zinc precursor, and other types of alkyl thiol and the like may be used in the case of sulfur precursor. In the case of oleic acid, stearic acid, myristic acid and the like may be used.

The first ZnS shell reaction temperature in step S120 is in the range of 200 to 280 ° C, and the reaction time can be in the range of 1 minute to 2 hours.

The second ZnS stock solution of step S120 may be of a different kind than the first ZnS stock solution of step S120. For example, zinc stearate as a Zn precursor, 1-dodecanethiol as a sulfur precursor, and octadecene as a solvent can be produced as a basic combination. At this time, in the case of the zinc precursor, zinc acetate, zinc oxide, zinc oxide, zinc acetylacetonate and the like may be used in addition to zinc stearate, and in the case of a sulfur precursor, the above-mentioned other alkyl thiol compounds may be used.

The second ZnS shell reaction temperature in step S120 is in the range of 180 to 300 ° C, and the reaction time can be in the range of 1 minute to 24 hours.

Hereinafter, the present invention will be described in more detail with reference to specific experimental examples.

Core quantum dot formation:

Four core quantum dots with a Cu / Ga precursor molar ratio of 1/1, 1/2, 1/4, and 1/8 were formed (samples 1-4 according to their molar ratios). For example, to synthesize a sample 4 CGS core quantum dot having a Cu / Ga precursor molar ratio of 1/8, 0.0625 mmol of copper iodide, 0.5 mmol of gallium iodide, 0.5 mL of 1-dodecanethiol (DDT) and 5 mL (OLA) was placed in a 50-mL three-neck flask to prepare a mixed solution, degassed and purged, and then heated to 180 ° C.

200 ºC A sulfur stock solution prepared by dissolving 2 mmol of sulfur (S) in 2 mL of 1-octadecene (ODE) was rapidly injected into the above mixed solution and maintained for 5 minutes to grow CGS core quantum dots.

ZnS shell formation:

To coat the core quantum dots with ZnS, a first ZnS stock solution consisting of 4 mmol of zinc acetate, 2 mL of 1-DDT, 2 mL of 1-ODE and 4 mL of oleic acid (OA) was added slowly to the solution containing each quantum dot at 220 ° C. After the addition, it was kept for 30 minutes (first shelling).

Then, a second ZnS stock solution consisting of 8 mmol of zinc stearate, 4 mL of 1-DDT and 8 mL of 1-ODE was slowly added dropwise to the flask containing the above reactant, and this second shell- -90 minutes (second shelling).

The CGS / ZnS quantum dots synthesized by this method were precipitated by adding hexane and ethanol, and the reaction byproducts were removed using a centrifuge. Finally, the quantum dots obtained by the refining process were redispersed in chloroform and used for device fabrication.

Formation of ZnO nanoparticles (NP):

ZnO nanoparticles were synthesized by solution - precipitation method.

5 mmol of tetramethylammoniumhydroxide (TMAH) and 10 ml of ethanol was slowly added at room temperature to a solution of 3 mmol of Zn acetate dihydrate dissolved in 30 ml of DMSO (dimethyl sulfoxide) And maintained for 1 hour. The synthesized ZnO nanoparticles were precipitated with excess acetone and redispersed in ethanol for optical characterization and spin coating of electron transport layer (hereinafter ETL).

QLED Manufacturing:

A white electroluminescent device including the above emitter of a single quantum dot was prepared. The stacking order is ITO / PEDOT: PSS HIL / PVK HTL / CGS / ZnS QD EML / ZnO NP ETL / Al.

First, the glass substrate having the patterned ITO anode was washed with distilled water, acetone and isopropanol, respectively, and treated with UV-ozone for 20 minutes. Coated with poly (ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS) (AI 4083) at 3000 rpm for 60 seconds and baked at 150 ° C for 30 minutes in an N ₂ atmosphere to form a 24 nm thick HIL. A solution of 0.05 g PVK (average M _W = 25000-50000) dissolved in 5 ml of chlorobenzene was spin-coated at 3000 rpm for 60 seconds on the HIL and baked under the same conditions as in HIL to form a 28 nm thick HTL.

A hexane dispersion of CGS / ZnS adjusted to have an optical density of 0.8 at 375 nm (QD concentration approximately 4 mg / ml) was spin coated on HTL at 2000 rpm for 20 seconds and dried at room temperature. After formation of the QD EML, a ZnO nanoparticle ethanol dispersion (concentration of 28-30 mg / ml) was spin coated at 1500 rpm for 60 seconds and baked at 60 ° C for 30 minutes to form a 44 nm thick ZnO NP ETL.

Finally, a 100 nm thick Al cathode was formed by thermal evaporation through a linear metal mask to complete the device.

A device using a PEN substrate instead of a glass substrate was also fabricated.

Evaluation tools:

UV-Vis absorption and PL spectra of the quantum dots were recorded with an absorption spectrometer (Shimadzu, UV-2450) and a 500 W xenon lamp-mounted spectrophotometer (PSI Inc., Darsa Pro-5200). The PL quantum efficiency absolute value of the diluted quantum dot dispersion was evaluated with a PL QY measuring system (C9920-02, Hamamatsu).

The composition analysis of the quantum dots was performed using an EDS-installed electroluminescence scanning electron microscope (JEOL-7800F) operating at 10 kV. Cu K _α The structures of quantum dots were analyzed using powder X-ray diffraction (XRD) (Rigaku, Ultima IV) using radiation.

In order to obtain a tomographic image of QDED and QDED, TEM operation was performed using Tecnai G2 F20 operating at 200 kV. The VBM (valence band maximum) of a sample 4 CGS / ZnS quantum dot with Cu / Ga = 1/8 was estimated using a PESA (Riken Keiki AC-2 Photoelectron Spectroscope) equipped with a deuterium lamp (input power 500 nW). For PESA measurement, a quantum dot film having a thickness of ~ 20 nm was prepared by spin-coating each quantum dot dispersion on an ITO glass substrate. To collect the decomposition PL afterglow curve, the quantum dot dispersion was excited with a 355 nm pulsed Nd: YAG laser (Spectron Laser System SL802G). The luminescence was dispersed by a 75 cm monochromator (Acton Research Corp. Pro-750) and amplified using an optical amplifier (Hamamatsu-Photonics Co. R928). Data were recorded on a LeCroy 9301 digital storage oscilloscope.

The EL spectrum of the QLED, Correlated Color Temperature (CCT), Commission Internationale de l'Eclairage (CIE) color coordinates, CRI and luminance-current density-voltage characteristics were measured using the Konica-minolta CS- 2000 spectrophotometer.

result:

4 is an EDS spectrum of CGS / ZnS QD prepared by varying the molar ratio of Cu / Ga precursor to 1/1, 1/2, 1/4 and 1/8 (Samples 1 to 4). In the actual quantum dots after the fabrication, the Cu / Ga molar ratio was slightly higher, 0.14, 0.29, 0.55, and 1.13, respectively.

Fig. 5 (a) shows the absorption spectrum and bandgap variation of samples 1 to 4 according to the experimental example of the present invention, (b) shows the normalized PL spectrum and fluorescence image, (c) It is a PL change graph expressed as a function of time.

Referring to FIG. 5A, the absorption spectrum is blue-shifted as the Cu / Ga molar ratio decreases.

6 shows the result of calculating the optical bandgap of each QD using the ( Ahν ) ² - hν relation ( A = absorption, h = Planck's constant, v = optical frequency). As shown in the box diagram of FIG. 5 (a), as the molar ratio of Cu / Ga decreases, the bandgap increases almost linearly from 2.5 eV to 3.1 eV.

In order to investigate the potential effects of Cu / Ga molar ratio on QD size, we compared XRD patterns for CGS / ZnS QD. Figure 7 (a) XRD patterns of Samples 1 to 4 according to Experimental Example of the present invention. As shown in FIG. 7 (a), all of the archetypal tetragonal chalcopyrite structures are shown, and all the FWHMs are the same. As a result, it can be seen that there is no difference in the size of the QD samples. As shown in FIG.

TEM observations of different samples showed no significant difference in size. 7B is a low magnification TEM photograph of a representative sample 4, and FIG. 7C is a high magnification TEM photograph of the sample 4. FIG. As can be seen, the size of the quantum dots is in the range of approximately 3.8-4.6 nm.

Referring back to FIG. 5, referring again to FIG. 5 (b), it can be seen that the second ZnS shell rings are all equally conducted for 40 minutes. As the Cu / Ga molar ratio decreases, the blue transition and the band gap increase as a whole, have. It can be confirmed that the PL is wider at the Cu-deficient quantum dots than at the quantum dots according to the present invention, which can not be observed at other visible light emission I-III-VI quantum dots.

FIG. 8 is a graph showing PL spectra of Samples 1 to 4 according to the experimental example of the present invention by Gaussian function fitting method. Each PL is decomposed into high-energy (HE) and secondary low-energy (LE) emissions.

HE luminescence occurs by radio-recombination of electrons and electrons within the conduction band CB (CB-to-V _Cu transition) as trapped electrons in the copper attacker (V _Cu ). The LE emission is obtained from Ga _Cu Lt; RTI ID = 0.0 &gt; or near &lt; / RTI &gt; And may be associated with new defect states such as Zn _Cu . These novel defects act as donor levels and participate in radioactive recombination with the V _Cu acceptor (donor-acceptor pair recombination).

The higher the donor concentration of Ga _Cu / Zn _Cu is, the more DAP will increase. Thus, as shown in FIG. 9, it can be seen that the contribution of DAP emission increases in PL as Cu / Ga becomes smaller.

In addition, since the V _Cu acceptor site provides a radioactive channel for CB-to-V _Cu and DAP transitions, its concentration plays a crucial role in determining the overall QY. Thus, QY increases from 26% of sample 1 to 73% of sample 4 (see FIG. 9 (a), which is a PL QY change graph of samples 1 to 4 according to the experimental example of the present invention).

Particularly in Sample 4, pure white light emission having a wide visible light range of blue-red is observed. Referring back to FIG. 5 (c), the PL change in the sample 4 is expressed as a function of the second shelling time. At the beginning of shelling (first shelling and second 20-second shelling), DAP emission is dominant and CB-to-V _Cu emission increases as the second shelling time increases. From this, it can be seen that the color temperature of the white PL can be adjusted by simply adjusting the shelling condition. As the second shelling time increases, QY also increases, reaching a peak value of 76% when the second shellling is 1 hour (see FIG. 9 (b), which is a PL QY graph expressed as a function of the second shelling time in Sample 4 ).

Figure 9 (c) is the UV-vis spectral change as a function of the second shelling time in sample 4. [ Referring to this, the bandgap of the quantum dots does not change when the shelling time changes, showing that the interface alloy does not occur in the CGS / ZnS core / shell during shelling.

In the case of Sample 4 of the Experimental Example, not only QY is sufficiently high for QLED but also white light emission in the entire visible light region is noted.

In the Experimental Example of the present invention, a white electroluminescent device including a single quantum dot emitter was manufactured using the sample 4.

10 (a) shows the structure of a QLED including a single quantum dot emitter manufactured according to the experimental example of the present invention. (b) is a cross-sectional TEM image of an actual device, (c) is a band diagram, (d) shows the white light emission of the device manufactured on the glass, and .

In order to make the band diagram shown in FIG. 10 (c), the VBM of the CGS / ZnS quantum dot was measured by PESA in the air.

11 shows the result of PESA measurement of Sample 4. Fig. IE was estimated to be 5.4 eV according to the empirical formula Y alpha (E-IE) ³ , where Y is the PL luminous efficiency, E is the incident light energy, and IE is the ionization energy. CBM (conduction band minimum) calculated using this VBM level of the CGS / ZnS quantum dot and the optical bandgap (3.1 eV obtained in FIG. 5 (a)) is 2.3 eV.

FIGS. 10 (c) and 10 (d) are images obtained by driving the actually fabricated device at 6 V. FIG. It can be seen that according to the present invention, not only the device of (c) but also the bent device of (d) can be manufactured. (C) and (d), except that the baking temperature of PEDOT: PSS and PVK was lowered to 120 캜 in consideration of the glass transition temperature of PEN (< 140 캜) Do. As shown in FIG. 10 (d), since it is possible to emit white electroluminescence from the curved QLED, it can be seen that a bent white plate can be manufactured.

FIG. 12A shows the collected EL spectrum, FIG. 12B shows the EL spectrum normalized to the HE EL wavelength, and FIG. 12C shows the CIE color coordinates of the white EL as a function of the applied voltage.

In the voltage-dependent EL spectrum change in FIG. 12 (a), the white EL is emitted only from the CGS / ZnS quantum dot, and there is no parasitic HTL emission contribution. Thus, it can be seen that the radioactive recombination of injected charges is limited to EML over the applied voltage range. In the conventional white EL device using CdSe, InP, etc., a white color is realized by mixing the spectrum of QD EML and neighboring CTL luminescence, whereas in the present invention, white luminescence is possible with only quantum dots. Further, in the conventional color mixing EL device, the exciton recombination region moves uncontrollably, and the EL spectrum tends to fluctuate severely depending on the applied voltage. However, the present invention is based on the fact that EL behavior stable to voltage change as shown in Figure 12 (b) And the CIE color coordinates are distributed in a narrow region of (0.286-0.294, 0.330-0.334) as shown in FIG. 12 (c).

12 (b), the EL is slightly red-shifted as the voltage increases. This is a common spectrum spread even in Cd-based QLED devices, and can be attributed to the field-induced quantum confinement Stark effect have.

Figure 13 shows the PL decay of CGS / ZnS QDs at 475 nm (CB-to-V _Cu For light emission) and 575 nm (for DAP). The mean life span ( t _av ) was 1.3 and 2.7 ms, respectively. Accordingly, the Auger (Auger) de-here the effect high drive voltage (or high QD charging) that, DAP emission having a longer t _av is Auger de-liable to occur here in the EL gain compared with the CB-to-V _Cu Competitiveness is lost. On the other hand, when the device is driven, joule heating is accompanied by causing a quantum dot thermal reflection in the device. Considering that at high temperatures LE DAP emission is more thermally driven than HE CB-to-V _Cu , the reduction of LE EL spectra at high voltages can be attributed in part to this Joule heating-related thermal imaging .

14 (a) is a current density-luminance variation according to a voltage in a white QLED, (b) is a current efficiency-EQE-power efficiency variation, and (c) is a graph of CRI-CCT variation.

Referring to FIG. 14A, a white QLED according to the present invention has a maximum luminance of 1007 cd / m ² at a driving voltage of 8.5 V (current density 314 mA / cm ² ). 14 (b), the maximum current efficiency, EQE and power efficiency are 3.6 cd / A, 1.9% and 1.9 lm / W at 6 V and 91 cd / m ² , respectively. These values are significantly improved compared to the conventional hybrid QD / CTL EL emitting white QLEDs with a high driving voltage of <700 cd / m ² and EQE <0.1%.

As can be predicted from the results of FIG. 12, the CRI and CCT values depend on the voltage, and when the voltage is 4-8.5 V, the values are 83-88 and 7494-8234 K, respectively. This CRI is quite high in the lighting field. 12 (c), just as the CIE color coordinates change in a voltage-dependent manner, the white EL becomes cool white as the voltage increases. Cool white with a CCT above 7000 K is too high for lighting standards. As another example for the implementation of warm white, a device was fabricated using a CGS / ZnS QD with Cu / Ga = 1/8 but a second ZnS-shelling with quantum dots lasting for 20 minutes instead of 1 hour As shown in Figure 5 (c), the HE CB-to-V _Cu Light is suppressed and warmer color).

FIG. 15 shows the results of the white QLED using the CGS / ZnS quantum dot for the second ZnS-Schering ring for 20 minutes, wherein (a) is the EL spectrum and (b) is the CIE color coordinate corresponding thereto. Referring to FIG. 15, it can be seen that a warm white EL having a 4700K CCT is implemented, and that a white color temperature can be conveniently adjusted by selecting a quantum dot having an appropriate spectrum distribution.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation in the embodiment in which said invention is directed. It will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the appended claims.

1 ... white quantum dot-light emitting element 10 ... substrate
20 ... anode 30 ... hole injection layer
40 ... Hole transport layer 70 ... Quantum dot luminescent layer
80 ... electron transport layer 90 ... cathode
100: QD 120: Core QD
130: ZnS shell

Claims (14)

Wherein the quantum dots of the quantum dot luminescent layer include an I-III-VI system ternary Cu-Ga-S or Ag-Ga-S or I-III-VI system As white quantum dots having component X-In-Ga-S or Zn-X-Ga-S (X = Cu, Ag) core quantum dots and ZnS shells,
In the ternary system, Cu: Ga or Ag: Ga or X: (In + Ga) or X: (Zn + Ga) in the sapphire component is 1:10 to 1:
In the case where In: Ga = (1-x): x in the quaternary component X-In-Ga-S or Zn: Ga = (1-x): x in the quaternary component Zn- 0.5 < x < 1,
And a white quantum dot-emission device having an emission spectrum including an entire visible light region from blue to red, wherein the white quantum dots show white light emission by combination of emission spectra of the quantum dots themselves. delete delete The white quantum dot-emitting device according to claim 1, wherein the core quantum dots are doped with Mn. The method of claim 4, wherein the molar ratio of Mn: Cu or Mn: Ag is in the range of more than 0 and 0.5 or less in the case of the ternary quantum dot, and the Mn: X molar ratio in the case of the quaternary quantum dots is in the range of more than 0 and 0.5 or less. device. The organic electroluminescence device according to claim 1, further comprising a cathode, a hole injection layer, and a cathode, wherein the hole injection layer is made of poly (ethylenedioxythiophene): polystyrene sulphonate (PEDOT: PSS), the hole transport layer is made of poly (9-vinlycarbazole) And a white quantum dot-emitting device. The white quantum dot-emitting device according to claim 1, wherein the hole transport layer is an organic material or an inorganic material, and the electron transport layer comprises ZnO nanoparticles. A quantum dot light emitting layer, and an electron transporting layer, wherein the step of forming the quantum dot light emitting layer comprises:
X-In-Ga-S or Zn-X-Ga-S (X-In-Ga-S or Ag-Ga-S or I- = Cu, Ag) core quantum dots and a ZnS shell are coated and baked,
The white quantum dots may be Cu: Ga or Ag: Ga in the ternary system or X: (In + Ga) or X: (Zn + Ga) in the sapphire component of 1:10 to 1:
In the case where In: Ga = (1-x): x in the quaternary component X-In-Ga-S or Zn: Ga = (1-x): x in the quaternary component Zn- 0.5 < x < 1,
Wherein the white quantum dot is a white quantum dot having an emission spectrum including an entire visible light region from blue to red, wherein white light emission is observed by combination of emission spectra of the quantum dots themselves. The method of claim 8,
X-In-Ga-S or Zn-X-Ga-S (X = Cu, Ag) or Ag-Ga-S or I-III-VI system ternary Cu- ) Forming core quantum dots;
An optional step of adsorbing Mn on the core quantum dot surface; And
And forming a ZnS shell on the core quantum dot. 10. The method of claim 9, wherein the forming of the core quantum dots is performed by mixing a precursor and a solvent and heating them. 10. The method of claim 9, wherein the step of forming the ZnS shell is performed by applying a ZnS stock solution. 12. The method according to claim 11, wherein the step of forming the ZnS shell is performed twice in succession. 13. The method according to claim 12, wherein the concentration and the reaction temperature of each ZnS stock solution are different from each other when the two successive steps are performed. 10. The method of claim 9, wherein forming the core quantum dot comprises:
A copper precursor, a gallium precursor, a sulfur precursor, and a solvent mixed solution by injecting a sulfur source,
Forming the ZnS shell comprises: applying a first ZnS stock solution to the mixed solution; And
Applying a second ZnS stock solution to the mixed solution,
The ZnS stock solutions include Zn precursors, sulfur precursors and octadecenes,
Wherein the first ZnS stock solution further comprises any one of oleic acid, stearic acid, and myristic acid.

Images