KR20190059632A - Fabricating methods of quantum dots-oxide composite and on-chip package quantum dots-LED using the same - Google Patents

Abstract

The present invention relates to a production method of a quantum dot-oxide composite, which improves fluorescence stability under degradation conditions without decreasing quantum efficiency (QY), and a production method of an on-chip package quantum dot-LED using the same. The production method of a quantum dot-oxide composite comprises the steps of: producing a quantum dot dispersion in which quantum dots are dispersed in a solvent; adding an oxide precursor to the quantum dot dispersion to produce a mixed solution; and placing the mixed solution in a thermo-hygrostat without adding a catalyst or water to the mixed solution to surround the quantum dots with oxides derived from the oxide precursor.

Description

METHOD FOR MANUFACTURING QUANTUM-OXIDE COMPOSITION AND ON-CHIP PACKAGE USING THE SAME <br> <br> <br> Patents - stay tuned to the technology METHOD FOR MANUFACTURING QUANTUM DOT-OXIDE COMPOSITE AND ON-

The present invention relates to a method for manufacturing a quantum dot-oxide composite in which quantum dots are distributed in a metal oxide, and an on-chip package quantum dot-LED manufacturing method using the same.

The quantum dots (QDs) having a semiconductor characteristic of a size of several tens of nanometers or less, that is, quantum dots (QDs), are different from the bulk particles due to the quantum confinement effect. As the size of the nanoparticles decreases, the bandgap of the nanoparticles increases, and as the size of the particles decreases, the emission wavelength becomes blue-shifted. In addition, when the particle size is extremely reduced, the proportion of the atoms or ions existing on the surface of the material increases. As a result, due to the extremely small size of the particles such as the lowering of the melting point or the decrease of the crystal lattice constant, It exhibits new optical, electrical and physical properties that could not be seen.

Among the semiconductor nanoparticles showing such changes in physical and optical properties, the colloidal II-VI compound semiconductor quantum dots are attracting much attention due to their high quantum yield (QY) of 60% or more and their optical and chemical stability. Typical II-VI compound semiconductor quantum dots include CdSe, and many studies have been conducted with high QY and stability characteristics.

Recently, studies on III-V compound semiconductor quantum dots (eg, InP) and I-III-VI chalcogenide-based quantum dots (eg, Cu-In-S) have been conducted to replace Ⅱ-VI compound semiconductor quantum dots It is actively proceeding. Existing research has focused on improving the QY of Cd replacement quantum dots and some successful cases have been reported.

However, it is a challenge to manufacture quantum dots having fluorescence stability for degradation environments such as long-term exposure to photons and heat. Quantum dots are commercially available in LCD backlight units (BLUs) as color conversion emitters in combination with blue LED pumping sources. In such applications, the Qdots are dispersed in a large-area polymer resin film and sandwiched between the two oxide gas barrier films so that the QD-resin composite film is not degraded by oxygen and water molecules. However, since such a structure is expensive, it is required to directly integrate QDs in LEDs as in an on-chip package. In such an on-chip package, securing the stability of a quantum dot in a deteriorated environment such as a high temperature or UV irradiation Should be preceded.

It is helpful to form thick shells, such as multiple shells or compositionally gradient shells, to improve the light stability and thermal stability of quantum dots, but it is not sufficient to enhance fluorescence stability under degradation conditions. Conventionally, methods for physically surrounding quantum dots by separately coating quantum dots with chemically stable oxides for optical stability have been proposed.

방법과 RM(reverse microemulsion) 방법이 잘 알려져 있다. 그러나, 실리카 반응 동안에 양자점 표면이 화학적으로 열화되어 궁극적으로는 QY를 상당히 감소시킨다는 문제가 있다. 적색 InP/ZnS 양자점에 대해 RM 방법으로 실리카를 코팅하게 되면 최초 QY인 30-50%가 15%까지 감소되는 것이 보고되어 있다. 다른 예로는 In₂O₃, ZnGa₂O₄, Al₂O₃ 등으로 양자점 표면을 개별 코팅하는 것이 있다. 그러나, 현재까지 제안된 산화물로 코팅하는 방법에서는 양자점 표면에 피할 수 없는 손상이 일어나기 때문에 QY가 낮아지게 된다는 한계가 있다.Typically, the silica formed by the sol-gel reaction is coated either individually on the quantum dot or embedding the quantum dot in silica. As a method of synthesizing TEOS with silica using a catalyst

Method and a reverse microemulsion (RM) method are well known. However, there is a problem in that during the silica reaction, the surface of the quantum dots is chemically deteriorated and ultimately the QY is considerably reduced. It has been reported that when the silica is coated by the RM method on the red InP / ZnS quantum dots, the initial QY of 30-50% is reduced by 15%. Another example is to coat the surfaces of the quantum dots separately with In ₂ O ₃ , ZnGa ₂ O ₄ , Al ₂ O ₃ and the like. However, in the method of coating with the oxide proposed so far, inevitable damage occurs on the surface of the quantum dots, so that QY is lowered.

A problem to be solved by the present invention is to provide a method for producing a quantum dot-oxide composite which improves fluorescence stability under degradation conditions without reducing QY.

Another object of the present invention is to provide an on-chip package quantum dot-LED manufacturing method using such a method of manufacturing a quantum dot-oxide complex.

According to another aspect of the present invention, there is provided a method for manufacturing a quantum dot-oxide composite comprising: preparing a quantum dot dispersion in which quantum dots are dispersed in a solvent; Adding an oxide precursor to the quantum dot dispersion to prepare a mixed solution; And placing the mixed solution in a thermohygrostat without adding a catalyst or water to the mixed solution to surround the quantum dots with an oxide derived from the oxide precursor.

The quantum dot may be a quantum dot of the core / shell structure. At this time, the core composition of the quantum dot may be a II-VI or III-V or I-III-VI compound semiconductor. In particular, the core of the quantum dot may be, for example, InP or ABX (A = Cu ⁺ , Ag ⁺ , B = In ^{3 +} , Ga ^{3 +} , X = S ^2- , Se ^{2 -} ).

Preferably, the temperature and humidity conditions of the thermo-hygrostat may be 10 to 100 ° C and 10 to 100%, respectively.

The solvent for preparing the quantum dot dispersion may be any one of toluene, chlorobenzene, chloroform and alkane solvents. Examples of the alkane-based solvent include hexane, octane, and the like.

According to the present invention, the quantum dot-oxide complex may be a particle in which a quantum dot is embedded in the oxide matrix. At this time, the oxide may be any one of silica, alumina, zirconia, and titania.

In order to obtain such a quantum dot-oxide complex, the oxide precursor may be any one of a silane series, an aluminum alkoxide series, a zirconium alkoxide series, and a titanium alkoxide series.

According to another aspect of the present invention, there is provided a method of manufacturing an on-chip package quantum dot-LED according to the present invention, wherein a thermosetting epoxy resin and a curing agent are added to the quantum dot- Producing; Applying the paste onto a surface mount LED mold; And thermally curing the applied paste.

According to the present invention, a quantum dot-oxide complex such as a quantum dot surrounded by an oxide can be provided, and excellent performance of the quantum dot can be maintained. Quantum dots in the quantum dot-oxide complexes maintain high fluorescence stability under degradation conditions.

The quantum dot-oxide composite according to the present invention does not deteriorate severely even in the UV irradiation environment or the thermal aging state. According to the experimental example, the first QY of the quantum dots of 80% was maintained at 75-78%.

The quantum dot-LED using the quantum dot-oxide complex produced by the method according to the present invention has little change in the quantum dot emission area even when the driving time is increased, and has high light conversion efficiency (LCE) and luminous efficacy LE) can be maintained.

As described above, according to the present invention, it is possible to provide a quantum dot-oxide composite as a light conversion material for LEDs having a high efficiency, and to provide an inexpensive and highly stable on-chip package quantum dot-LED.

1 is a flow chart for explaining a method of manufacturing a quantum dot (QD) -oxide complex according to the present invention.
FIG. 2 (a) shows the change in PL QY over time of InP / ZnSeS / ZnS QD after TMOS addition according to the experimental example of the present invention. Figure 2 (b) shows PL spectra and UV-irradiated fluorescence images of pure QD and QD dispersions with TMOS treatment for 12 hours.
FIG. 3 (a) shows the change in PL QY of InP / ZnSeS / ZnS QD after TEOS addition instead of TMOS for preparing composite sample 2 according to the experimental example of the present invention. Figure 3 (b) shows the PL spectra and UV-irradiated fluorescence images of QD dispersion with pure QD and 12 hours TEOS treatment.
Fig. 4 TEM images of pure QD (QD sample 1) and QD-silica complex (composite sample 1).
5 is a photograph of an InP / ZnSeS / ZnS QD-silica composite (composite sample 1).
Figure 6 (a) shows the change in PL intensity over time of InP / ZnSeS / ZnS QD during RM silica reaction with TEOS and subsequent NH ₄ OH addition. Figure 6 (b) compares the PL intensities of QD-QD (QD sample 1), QD-silica composite (composite sample 1) according to the present invention and QD-silica composite according to the comparative RM method (composite composite 1) It is.
7 (a) is a TEM image of Composite Comparative Example 1 and (b) is a TEM image of Composite Comparative Example 2. Fig.
(Composite sample 1) PL according to the present invention with respect to the elapsed time of UV exposure. Fig. 8 (a) shows a change in PL QD of pure QD (QD sample 1) Represents a change in intensity. (c) shows a change in the relative QD emission area calculated from (a) and (b).
9 (a) shows the variation of the pure QD (QD sample 1) PL intensity with the elapse of 85 ° C / 85% exposure time, (b) shows the QD- Silica composite (composite sample 1). (c) shows a change in the relative QD emission area calculated from (a) and (b).
Figure 10 shows an on-chip package QD-LED (QD-LED comparison example) fabricated with (a) pure QD and (b) a QD- And the EL spectrum of the QD-LED (QD-LED Experimental Example 1).
Fig. 11 shows an on-chip package QD-LED (QD-LED comparison example) manufactured with (a) pure QD at a driving current of 60 mA and QD- (Experimental Example 1 of QD-LED) shows the change of EL spectrum according to driving time.
Fig. 12 is a plot of the (QD-LED Comparative Example, QD-LED Experimental Example 1) on-chip package QD-LEDs fabricated with pure QD and QD- (a) the change in the relative QD emission area and (b) the change in the LCE-LE of the QD-LED.
13 (a) is a TEM image of a QD-silica composite (composite sample 3). (b) shows the change of the EL spectrum according to the driving time of the on-chip package QD-LED (QD-LED Experiment 2) manufactured with the composite sample 3 at a driving current of 60 mA. (c) shows the change of the relative QD emission area.

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 flow chart for explaining a method of manufacturing a quantum dot (QD) -oxide complex according to the present invention.

Referring to FIG. 1, a quantum dot dispersion is first prepared (S1).

The quantum dot dispersion is obtained by dispersing quantum dots in a solvent.

The quantum dot may be a quantum dot of the core / shell structure. At this time, the core composition of the quantum dot may be a II-VI or III-V or I-III-VI compound semiconductor. In particular, the core of the quantum dot may be, for example, InP or ABX (A = Cu ⁺ , Ag ⁺ , B = In ^{3 +} , Ga ^{3 +} , X = S ^2- , Se ^{2 -} ).

The quantum dot core may be prepared by a hot colloid method, a solvothermal method, or heating-up or hot-injection, and the shell may be prepared by a cation exchange process ), A solvent heating method, and the like. Although the present invention is not limited to the form, composition and manufacturing method of a specific quantum dot, an example of a preferable method of quantum dot synthesis will be described below.

First, the step of growing the core QD from the solution containing the quantum dot precursors is performed. The mixed solution prepared by mixing the QD precursor and the solvent is heated to grow the core QD first. Heating of the mixed solution can be done in several steps. First, the degassing can be performed by heating at a degassing temperature, for example, 120 deg. Thereafter, the temperature can be raised to a growth temperature, for example, 240 ° C. At this time, N ₂ purging can be performed.

Next, a shell is formed. A shell can be formed by applying a stock solution for forming a shell to a mixed solution in which core QD is formed. The step of forming the shell may be performed two or more times in succession. At this time, the concentration of the stock solution in each step, the reaction temperature and the time may be different. The temperature of the second reaction may be higher or longer.

As such, the shells may be formed in multiple, e.g., double or triple, and each layer may have a different composition. The composition at this time may vary discontinuously or continuously. These multi-shells have excellent core QD passivation effects. As a result, QY of the quantum dot can be improved. When the shell is formed, PL (photoluminescence) and QY are both improved as compared with the core QD state, so it is preferable to use a core / shell structure as the quantum dot.

The solvent for preparing the quantum dot dispersion is of a nature capable of dispersing the quantum dots. Preferably, it may be any one of toluene, chlorobenzene, chloroform and alkane solvents. Examples of the alkane-based solvent include hexane, octane, and the like.

In general, the surface of the quantum dot is hydrophobic. The solvent capable of dispersing such quantum dots may be polar or non-polar in an organic solvent, and it is preferable in the subsequent process not to be mixed with water.

Next, an oxide precursor is added to the quantum dot dispersion to prepare a mixed solution (S2).

The oxide precursor may be one selected from the group consisting of silane series, aluminum alkoxide series, zirconium alkoxide series, and titanium alkoxide series. Table 1 below shows examples of various oxide precursors.

Next, the mixed solution is placed in a thermo-hygrostat to surround the quantum dots with an oxide derived from the oxide precursor (S3).

At this time, no catalyst or water is artificially added to the mixed solution. The mixed solution may be left in a stirred state for a uniform reaction.

The temperature condition of the thermo-hygrostat may be 10 to 100 ° C and the relative humidity condition may be 10 to 100%. If the temperature of the thermo-hygrostat is lower than 10 ° C, the decomposition reaction rate of the oxide precursor is too slow. If the temperature of the thermo-hygrostat is higher than 100 ° C, an unwanted reaction may occur in the mixture. The relative humidity of the thermo-hygrostat should be such that a small amount of water vapor sufficient to cause hydrolysis of the oxide precursor can be supplied. At less than 10% relative humidity, the supply of water vapor is not sufficient and the decomposition rate of the oxide precursor is too slow.

The reaction time may vary depending on the desired oxide coating thickness, whether to encapsulate the oxide individually, or whether to embed the quantum dots in the oxide matrix, and typically 20-24 hours, particles with quantum dots embedded in the oxide matrix can be obtained Respectively. Then, the quantum dot-oxide complex can be obtained by centrifugation, washing and drying.

방법과 RM 방법에서는 촉매를 사용하여 TEOS를 실리카로 합성한다. 이들 방법에서는 상 전이 등을 위해 리간드 교환이 일어나고, 촉매가 QD 표면을 화학적으로 부식시킬 수가 있다. 본 발명에서는 촉매를 사용하지 않는다. RM 방법에서는 특히 촉매로서 사용하는 암모니아(NH₄OH) 때문에 물이 더 공급된다. 본 발명에서는 물을 첨가하지 않고 항온항습기 안에서 수증기 상태로 공급한다. 촉매와 물이 없이 진행되는, 수증기에 의한 가수 분해 반응은 급격한 반응이 없고, 양자점 표면에 대한 손상이 없이 진행된다.Known catalysts

In the method and the RM method, TEOS is synthesized as silica using a catalyst. In these methods, ligand exchange occurs for phase transition and the like, and the catalyst can chemically corrode the QD surface. In the present invention, no catalyst is used. In the RM method, water is further supplied because of ammonia (NH ₄ OH) used as a catalyst in particular. In the present invention, water is supplied in a vapor state in a constant temperature and humidity chamber without adding water. The hydrolysis reaction by the water vapor, which proceeds without the catalyst and water, has no abrupt reaction and proceeds without any damage to the surface of the quantum dots.

Also, when the solvent in the quantum dot dispersion is selected so as not to be mixed with water, water vapor can be supplied only to the surface of the quantum dots without being mixed with the solvent, and can be effectively used for the hydrolysis reaction of the oxide precursor. This hydrolysis reaction on the surface allows the oxide to uniformly surround the surface of the quantum dots.

Through the above step S3, a quantum dot-oxide complex in the form of particles such as the quantum dots embedded in the oxide matrix can be produced. The reaction time and the like can be controlled to form the oxide coated on the periphery of the quantum dot. Since the reaction in step S3 is performed slowly without damaging the surface of the quantum dots, the quantum dot-oxide complex of the present invention maintains excellent characteristics of the quantum dot as compared with the case where the rapid sol-gel reaction proceeds.

The quantum dot-alumina composite can be prepared when the oxide precursor is a silane-based compound, and the quantum dot-alumina composite can be prepared when the oxide precursor is an aluminum alkoxide-based compound. When the oxide precursor is a zirconium alkoxide- Complex can be produced. Further, when the oxide precursor is titanium alkoxide-based, a quantum dot-titania composite can be prepared.

In one embodiment, InP / ZnSeS / ZnS quantum dots were prepared by applying multiple shells to InP quantum dots, and red emission quantum dots having an absolute QY of 80% were prepared. Then, using a silane series TMOS as an oxide precursor, InP / ZnSeS / ZnS quantum dot-silica complex. In another embodiment, TEOS is used as an oxide precursor. In another embodiment, a green light emitting quantum dot is provided and a quantum dot-silica composite is prepared using APTMS as an oxide precursor.

The quantum dot-oxide composite prepared by the method according to the present invention can be used as a light conversion material for LED. In particular, it can be used as a photo-conversion material by being used in on-chip package LED manufacturing.

The method for manufacturing an on-chip package quantum dot-LED according to the present invention comprises the steps of: preparing a paste by adding a thermosetting epoxy resin and a curing agent to the quantum dot-oxide composite produced according to the above steps S1 to S3; Applying the paste onto a surface mount LED mold; And thermally curing the applied paste.

As described above, the present invention relates to passivation of quantum dots physically surrounding quantum dots with oxides, securing luminescence stability of quantum dots through the passivation, and further to application as a light conversion material for LEDs.

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

Experimental Method:

QD  Sample 1: Red light emission InP / ZnSeS / ZnS QD  synthesis

For the red luminescent InP / ZnSeS / ZnS multi-shell QD synthesis, 0.45 mmol of indium chloride (InCl ₃ , 99.999%), 2.2 mmol of zinc chloride (ZnCl ₂ , 99.999% The mixed solution was prepared by adding oleylamine (OLA, 70%) into a three-neck flask, and the mixed solution was degassed by heating at 120 ° C for 1 hour, then purged with N ₂ and heated to 180 ° C . Then, 0.35 ml of tris (dimethylamino) phosphine (P (N (CH ₃ ) ₂ ) ₃ ), P (DMA) ₃ , 97%) was rapidly injected and the mixture was kept at that temperature for 25 minutes. . Then, a ZnSeS intermediate shell with a composition gradient was stepwise grown by alternately injecting anions and cation shell precursors in the following manner: Se stock solution (0.12 mmol of selenium (Se, 99.99%), 1 ml of trioctylphosphine TOP, 90%), and the mixture was reacted at 200 DEG C for 30 minutes. Then, Zn stock solution (1.58 mmol of zinc stearate dissolved in 4 ml of octadecene (ODE, 90%)) was injected and reacted at 220 ° C. for 30 minutes. Subsequently, a Se-S stock solution (0.06 mmol Se and 2 mmol sulfur (S, 99.99%) dissolved in 1.6 ml of TOP) was injected and reacted at 240 ° C. for 30 minutes. And allowed to react at 260 DEG C for 30 minutes. As the last step of the ZnSeS intermediate shell, another Se-S stock solution (S, 0.02 mmol Se and 4 mmol sulfur (S, 99.99%) dissolved in 2 ml of TOP) was injected and reacted at 280 ° C for 30 minutes Next, the Zn stock solution was injected again and reacted at 300 ° C for 60 minutes.

To continuously grow the cells outside the ZnS, 5 ml of 1-dodecanethiol was dropwise added dropwise, followed by reaction at 200 ° C for 60 minutes. For the multi-shell InP / ZnSeS / ZnS QD, 3 mmol of zinc acetate (98%) was dissolved in 3 ml of oleic acid (90%) and the reaction was maintained at 190 ° C for 120 min. Respectively. After the reaction was cooled, the synthesized InP / ZnSeS / ZnS QD was dispersed in hexane, precipitated by addition of excess ethanol, and purified by a centrifugal separator (8000 rpm, 15 minutes) using hexane / Respectively. The purified InP / ZnSeS / ZnS QD was redispersed in hexane or toluene. Hereinafter, pure red luminescent InP / ZnSeS / ZnS QD not enclosed by oxide is referred to as QD sample 1.

Composite Sample 1: TMOS  Using red light InP / ZnSeS / ZnS QD - Preparation of silica complex

QD Samples 1 were run and then 2 ml of a pure InP / ZnSeS / ZnS QD-toluene dispersion, adjusted to an optical density of 2.0 at 574 nm, was added to 18 ml of toluene, and the optical density at 574 nm 20 &lt; / RTI &gt; 1 ml of an oxide precursor, TMOS, was added to the QD dispersion, and the mixture was stirred in a thermohygrostat (TH-PE-100, JEIO Tech., Korea) set at 30 ° C and a relative humidity of 70%. Generally, when the reaction was allowed to take place for 20 to 24 hours, aggregation of QD-embedded silica was observed in the solution. The agglomerated particles were precipitated using a centrifuge (8000 rpm, 10 minutes) and washed twice with excess acetone. The red luminescent InP / ZnSeS / ZnS QD-silica composite (using TMOS) thus prepared is hereinafter referred to as composite sample 1.

Composite Sample 2: TEOS  Using red light InP / ZnSeS / ZnS QD - Preparation of silica complex

Experiments using TEOS instead of TMOS were carried out without changing other conditions. In addition to injecting TEOS into the QD solution, other conditions were similar to the complex sample 1. The red luminescent InP / ZnSeS / ZnS QD-silica complex (using TEOS) is hereinafter referred to as composite sample 2.

Complex Comparative Example  One : RM  Red emission by method InP / ZnSeS / ZnS QD - Preparation of silica complex

Experiments have also been carried out to passivate the red luminescent InP / ZnSeS / ZnS QD according to the conventional RM method. In the RM method, an ammonia catalyst is used.

1.7 ml of IGEPAL 520 were dissolved in 10 ml of cyclohexane and this was added to 0.1 ml of a pure InP / ZnSeS / ZnS QD-toluene dispersion, the optical density at 574 nm being adjusted to 2.0. Subsequently, 80 占 퐇 of TEOS was injected into the mixture, followed by stirring for 30 minutes. Then, 0.04 ml of ammonia (NH ₄ OH, 28 wt%) was added to allow hydrolysis of TEOS and allowed to react for 24 hours. The agglomerated particles were precipitated using a centrifuge (8000 rpm, 10 minutes) and washed twice with excess acetone. The red luminescent InP / ZnSeS / ZnS QD-silica complex (RM method, 0.04 ml ammonia) is hereinafter referred to as Composite Comparative Example 1.

Complex Comparative Example  2 : RM  Red emission by method InP / ZnSeS / ZnS QD - Preparation of silica complex

Composite The same as Comparative Example 1 except that 0.3 ml of ammonia was used instead of 0.04 ml of ammonia. The red luminescent InP / ZnSeS / ZnS QD-silica composite (RM method, 0.3 ml ammonia) prepared by this method is hereinafter referred to as Composite Comparative Example 2.

QD  Sample 2: Green light emission InP / ZnSeS / ZnS QD  synthesis

In this experiment, green luminescent InP / ZnSeS / ZnS quantum dots were prepared. The emission wavelength can be changed by adjusting the composition ratio of the constituent elements. The pure green emitting InP / ZnSeS / ZnS QD, which is not surrounded by oxide, is called QD sample 2.

Composite Sample 3: Green Glow InP / ZnSeS / ZnS QD - Preparation of silica complex

And a green luminescent InP / ZnSeS / ZnS quantum dot as in QD Sample 2. The overall reaction is similar to the red luminescent InP / ZnSeS / ZnS QD-silica complex experiment of composite sample 1. As the oxide precursor, APTMS ((3-Aminopropyl) trimethoxysilane) was used instead of TMOS. The green luminescent InP / ZnSeS / ZnS QD-silica complex (using APTMS) is hereinafter referred to as composite sample 3.

QD -LED manufacturing

To prepare the QD-LED, 6 mg of pure QD (QD sample 1) and 18 mg of QD-silica complex (composite sample 1 and composite sample 3) were mixed with 0.3 g thermosetting epoxy resin (YD-128, Kukdo Chem. Korea). To this QD-resin mixture, 0.3 g of a curing agent was added (KFH-271, Kukdo Chem., Korea). The finished paste was dispensed onto a surface mount type blue InGaN LED (? = 455 nm) mold and cured through a thermal curing process at 90 占 폚 for 1 hour and 120 占 폚 for 30 minutes. The QD-LED manufactured by the QD-LED is QD-LED Comparative Example, the QD-LED manufactured by the composite sample 1 is QD-LED Experimental Example 1, and the QD-LED manufactured by the composite sample 3 is QD-LED Experimental Example 2 .

Table 2 summarizes the contents of each experimental example.

Stability test

QD samples, composite samples were completely dried in a 60 &lt; 0 &gt; C vacuum oven and powdered. All powders were packed in a stainless steel sample holder (diameter 7 mm, depth 0.5 mm) and deteriorated by exposure to UV radiation and 85 [deg.] C / 85% relative humidity conditions for a period of time.

For the UV irradiation test, continuous UV irradiation was performed for 120 hours using a 365 nm-multiband UV lamp and the change in PL intensity over time was monitored.

In the case of a thermal aging test, it was left in a thermostat for a predetermined time.

Evaluation tools:

To obtain the quantum dot image, a TEM operation was performed using JEM-2100F (JEOL Ltd.) operating at 200 kV. The PL spectra of the quantum dots were recorded with a 500 W xenon lamp-equipped spectrophotometer (PSI Inc., Darsa Pro-5200). The PL QY absolute values of the diluted QD dispersions were evaluated with a PL QY measurement system (C9920-02, Hamamatsu).

The EL (electroluminescence) data of the QD-LED, that is, the EL spectrum and the luminous efficiency (LE) were measured with a diode array analysis system (PSI Co. Ltd).

Experiment result:

FIG. 2 (a) shows changes in PL QY of InP / ZnSeS / ZnS QD after addition of TMOS for preparing composite sample 1 according to the experimental example of the present invention. Original QY (80%) of pure QD (QD sample 1) is starred. The error bar is according to the 5th measurement. (b) shows PL spectra and UV-irradiation fluorescence images of pure QD (black solid line) and QD dispersion (red solid line) subjected to 12 hours TMOS treatment. The PL excitation wavelength was 450 nm.

The pure red luminescence InP / ZnSeS / ZnS QD of the QD sample 1 has a ZnSeS intermediate composition gradient shell and ZnS outermost shell which increase in ZnS from the core to the outside, and as shown in FIG. 2 (b) 611 nm and QY is 80%. When 1 ml of TMOS was added to the 20 ml QD toluene dispersion, the QY decreased from 80% to 77% as the reaction time elapsed as shown in FIG. 2 (a), but after the reaction time elapsed, the overall QY value Is maintained at 75-78%.

Referring to FIG. 2 (b), the PL spectrum of the QD solution reacted for 12 hours is almost the same as the PL spectrum of the pure QD solution, and QY is 75%. Thus, it can be seen that the QD-silica complex can be prepared without damaging the QY of the InP-based QD according to the present invention.

FIG. 3 (a) shows the change in PL QY of InP / ZnSeS / ZnS QD after TEOS addition instead of TMOS for preparing composite sample 2 according to the experimental example of the present invention. Original QY (80%) of pure QD (QD sample 1) is starred. The error bar is based on the third measurement. FIG. 3 (b) shows PL spectra and UV-irradiated fluorescence images of QD dispersions (red solid lines) subjected to pure QD (black solid line) and 12-hour TEOS treatment. The PL excitation wavelength was 450 nm.

Referring to FIG. 3 (a), when the TEOS was injected into the QD solution, the QY was reduced to 52%, but the reaction time was maintained at 50-55%. From this, it can be inferred that the degree of deterioration of the QD surface by TEOS is higher than that of TMOS by removing the organic ligand on the QD surface. Referring to FIG. 3 (b), the PL intensity of the QD solution subjected to the TEOS reaction for 12 hours is lower than the PL intensity of the pure QD solution, and QY is 50%.

Figure 4 is TEM images of pure QD (QD sample 1) and QD-silica complex (composite sample 1). 4 (a) and 4 (c) are low magnification TEM images, and FIGS. 4 (b) and 4 (d) are high magnification TEM images. (a) and (b) are for pure QD, and (c) and (d) are for QD-silica complex.

As shown in the pure QD TEM image of FIGS. 4 (a) and 4 (b), the InP / ZnSeS / ZnS QD has a diameter of about 7 nm, which is larger than a general single QD or multiple shell QD having a diameter of 5.5 nm It is big. This means that the lattice constant mismatch is effective to alleviate the interfacial stresses of the InP core and ZnS outermost shell at 7.7%. In the TEM image of the QD-silica composite of FIGS. 4 (c) and 4 (d), each QD is embedded in a silica matrix. The QD in the matrix is distributed very uniformly without noticeable aggregation, and no PL is caused by FRET (Forster resonant energy transfer).

The InP / ZnSeS / ZnS QD-silica complex was completely dried in powder form as shown in FIG. 5 and used for stability test under deteriorated condition. 5 is a photograph of an InP / ZnSeS / ZnS QD-silica composite (composite sample 1), wherein (a) is a photograph taken in natural light and (b) is a photograph taken under UV lamp.

In order to confirm the excellence of preserving the original QY of the QD according to the present invention, experiments for passivating the InP / ZnSeS / ZnS QD according to the conventional RM method proceeded to the composite comparative examples 1 and 2 described above.

6 (a) shows changes in the PL intensity over time of the InP / ZnSeS / ZnS QD during the RM silica reaction comprising TEOS and subsequent NH ₄ OH added to pure QD for preparation of the composite Comparative Example 1. Figure 6 (b) compares the PL intensities of QD-QD (QD sample 1), QD-silica composite (composite sample 1) according to the present invention and QD-silica composite according to the comparative RM method (composite composite 1) It is. The PL excitation wavelength was 450 nm.

Referring to Figure 6 (a), TEOS is compared with the PL intensity (red graph) of pure QD, as is the case with TEOS added to the QD dispersion as in the previous composite sample 2 (Figure 3). QD cyclohexane dispersion The PL loss was large. PL was shown 0.5 hour after TEOS addition (purple graph). The addition of NH ₄ OH for hydrolysis and condensation further reduced the PL intensity of the QD dispersion. The PL intensities immediately after addition of NH ₄ OH (0 h) and after 1 h (1 h) are almost the same (orange, yellow and green graphs respectively). This rapid decrease in InP QD PL intensity is similar to that reported in previous studies (30-50% → 15%), and some synthetic parameters such as the amount of NH ₄ OH can not be avoided.

In order to alleviate the PL reduction in the silica reaction by the RM method, two different NH ₄ OH contents were tested to prepare composite COMPARATIVE EXAMPLE 1 and COMPLEX COMPARATIVE EXAMPLE 2. However, changing the amount of NH ₄ OH did not help to minimize PL reduction. Instead, it affected the morphology of the QD-silica complex.

7 (a) is a TEM image of Composite Comparative Example 1 and (b) is a TEM image of Composite Comparative Example 2. Fig. Compared with Comparative Example 1, the amount of ammonia in the composite Comparative Example 2 is large. As the amount of ammonia increases, only the shape of the final complex changes to spherical shape.

Referring again to Figure 6 (b), the PL spectra of the three powder samples can be seen. FIG. 6 (b) shows a QD-silica composite according to the present invention (composite sample 1, TMOS-based catalyst-free method) and a QD-silica composite according to the comparative RM method 1, TEOS-based RM method).

The PL intensity (red graph) of the composite sample 1 according to the present invention is very similar to the PL intensity (black graph) of pure QD, but the PL intensity (pink graph) of the composite comparative example 1 is very low. As described above, it can be seen that the method of producing the QD-oxide complex according to the present invention is advantageous for effectively preventing deterioration of the surface of the QD accompanied by the conventional silica reaction and maintaining the original QY of the QD as much as possible.

To demonstrate the efficacy of silica embedding contributing to QD stability, pure QD (QD sample 1) and the QD-silica complex according to the present invention (composite sample 1) were exposed to an atmospheric UV irradiation environment (365 nm). The results are summarized in FIG.

(Composite sample 1) PL according to the present invention with respect to the elapsed time of UV exposure. Fig. 8 (a) shows a change in PL QD of pure QD (QD sample 1) Represents a change in intensity. (c) shows a change in the relative QD emission area calculated from (a) and (b).

Referring to FIGS. 8A and 8B, the PL intensity decreases with exposure time in the order of 0 hours, 10 minutes, 1 hour, 2 hours, 5 hours, 10 hours, and 15 hours. Referring to FIG. 8 (c), after 15 hours, the composite sample 1 (red circle) retained 80% of the initial PL intensity, while a more significant decrease (42%) in pure QD . As described above, it can be confirmed that the light stability is increased when the quantum dots are surrounded by the oxide as in the present invention.

Subsequently, the two samples were placed in a 85 ° C and 85% relative humidity thermostat for 144 hours. Figure 9 summarizes the results.

9 (a) shows the variation of the pure QD (QD sample 1) PL intensity with the elapse of 85 ° C / 85% exposure time, (b) shows the QD- Silica composite (composite sample 1). (c) shows a change in the relative QD emission area calculated from (a) and (b). 85 ° C / 85% exposure is a significant high temperature and high humidity environment, simulating the harsh environment in which QD-LEDs are used.

Referring to Figures 9 (a) and 9 (b), 0 hour, 1 hour, 5 hours, 24 hours, ... , And 144 hours, the PL intensity decreases as the exposure time elapses. Referring to FIG. 9 (c), the relative QD emission area of the composite sample 1 (red circle) was reduced by only 30%, while that of pure QD (black circle) was reduced by 53% even after a considerable exposure time. Although silica acts as a physical barrier to protect QD in an external degradation environment and serves to inhibit deterioration of the QD surface, it is difficult to completely maintain PL by silica passivation. It is to be understood that the amorphous silica produced by the sol-gel reaction has a porous network structure (porosity of 10-15%), which allows oxygen and water vapor molecules to reach the QD surface and thus oxidation and / or corrosion . However, the PL preservation effect is superior to that without silica.

QD-LED Comparative Example and QD-LED Experimental Example 1 After manufacture, EL spectra were measured at a relatively high input current of 60 mA.

Figure 10 shows an on-chip package QD-LED (QD-LED comparison example) fabricated with (a) pure QD and (b) a QD- And the EL spectrum of the QD-LED (QD-LED Experimental Example 1) (red graph). To calculate the blue-red light conversion efficiency, the EL spectrum of a 60-mA driven blue LED was also examined (blue graph). The light conversion efficiency (LCE) was evaluated by the spectral integral ratio of converted QD emission versus blue LED emission consumed for conversion.

10 (a) and 10 (b), the LCE of the QD-LED comparative example is 46%, and the LCE of the QD-LED Experimental Example 1 is 48%. Thus, a similar LCE between the two again proves that the complex according to the present invention can very effectively preserve the original QY of pure QD. In general, there is a concern that QD may lose its original luminescence intensity in a device-driven environment due to the strong photon flux from the LED and significant heat affecting the QD. However, according to the present invention, since the oxide passivates the QD very effectively, the excellent properties of the QD can be substantially preserved even after long driving, so that the QD-LED can be stably maintained and the life can be prolonged.

As can be deduced from the TEM image of FIG. 4, the QD interval in the QD-silica composite powder will increase relative to pure QD. As a result, the QD emission by FRET is reduced in the QD-LED fabricated by the QD-silica composite. In general, on-chip package QD-LEDs cause light scattering due to QD cohesion in the polymer resin or difference in refractive index between resin and QD, and the photon flux emitted to the outside is reduced. In particular, the difference in refractive index can be reduced by creating a silica-based QD complex, allowing intermediate refractive index values between the QD and the resin. This reduction in FRET and light scattering can improve the LCE of devices made of silica-based QD composites rather than pure QDs.

Then, the QD-LED Comparative Example and the QD-LED Experimental Example 1 were driven for 100 hours at a driving current of 60 mA.

Fig. 11 shows an on-chip package QD-LED (QD-LED comparison example) manufactured with (a) pure QD at a driving current of 60 mA and QD- (Experimental Example 1 of QD-LED) shows the change of EL spectrum according to driving time. The left inset is the EL image in the initial state and after 100 hours of driving.

11 (a) and 11 (b), the QD-emission intensity of the QD-LED Experimental Example 1 is slightly reduced while the driving time elapsed from 0 hours to 100 hours ), And in the case of the QD-LED comparison example, QD light emission occurs (see FIG. 11 (a)). As a result, as shown in the inset in FIG. 11, a more noticeable EL color change is observed after driving for 100 hours in the QD-LED comparative example manufactured with pure QD.

The change in QD emission area was also measured according to the driving time.

Fig. 12 is a plot of the (QD-LED Comparative Example, QD-LED Experimental Example 1) on-chip package QD-LEDs fabricated with pure QD and QD- (a) the change in the relative QD emission area and (b) the change in the LCE-LE of the QD-LED. The red circle in the graph is QD-LED Experimental Example 1 and the black circle is a QD-LED comparative example.

Referring to FIG. 12 (a), QD-LED having 65% of the initial value in the case of the QD-LED without silica embedding after 100 hours of driving, and 88% of the initial value in case of QD-LED Experimental Example 1 with silica embedding %. &Lt; / RTI &gt; The silica barrier protects the QD against such a high blue photon flux and in a thermal LED driving environment at 50 ° C (temperature associated with a 60 mA drive current) air atmosphere. Due to the loose structure of the epoxy encapsulant used in QD packaging, atmospheric gas species can easily reach the QD-silica complex and penetrate into the QD through the porous channels of silica. This causes deterioration of QD. Even so, the photodegradation of the QD embedded in the silica matrix is delayed, with only 12% lost after 100 hours of operation.

As a result of calculating the LCE change over time with reference to the result of FIG. 12 (a), as shown in FIG. 12 (b), after driving for 100 hours, the QD- In the case of Experimental Example 1, it changed from 48 to 42%. QD-LED The LE of Experimental Example 1 is 26.3 lm / W, which is higher than the LE of Comparative Example of QD-LED of 24.7 lm / W. The change with time of LE is also the same as the change in relative QD emission intensity or LCE. Referring to FIG. 12 (b), after driving for 100 hours, the QD-LED was changed from 24.7 to 19.4 lm / W in the comparative example and from 26.3 to 23.8 lm / W in the case of the QD-LED Experimental Example 1.

As a result, it can be concluded that the QD-oxide composite manufacturing method according to the present invention provides a practical means of manufacturing a QD-LED system with high efficiency and high stability by effectively passivating QD as well as QD of QD as much as possible Do.

On the other hand, the quantum dots used in the experimental examples are based on InP, but it is of course possible to apply the method according to the present invention to quantum dots of other compositions. Although the above results are related to red light emitting quantum dots, similar results can be obtained when using green light emitting quantum dots as in the case of composite sample 3 and QD-LED Experimental Example 2.

13 (a) is a TEM image of a QD-silica composite (composite sample 3). (b) shows the change of the EL spectrum according to the driving time of the on-chip package QD-LED (QD-LED Experiment 2) manufactured with the composite sample 3 at a driving current of 60 mA. (c) shows the change of the relative QD emission area.

As shown in FIG. 13 (b), in the case of QD-LED Experimental Example 2, there was almost no EL intensity change after driving for 100 hours, and it was confirmed that the relative QD luminescence area as shown in FIG. As described above, the QD-oxide complex according to the present invention can form a QD-oxide complex while preserving the QY of the QD regardless of the kind of the quantum dots and the oxide precursor.

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.

Claims (5)

Preparing a quantum dot dispersion in which quantum dots are dispersed in a solvent;
Adding an oxide precursor to the quantum dot dispersion to prepare a mixed solution; And
And placing the mixed solution in a constant-temperature and humidity chamber without adding a catalyst or water to the mixed solution to surround the quantum dots with an oxide derived from the oxide precursor. The method of claim 1, wherein the temperature and humidity conditions of the thermo-hygrostat is 10 to 100 ° C and 10 to 100%. The method of claim 1, wherein the solvent is any one of toluene, chlorobenzene, chloroform, and an alkane-based solvent. The method of claim 1, wherein the oxide precursor is one selected from the group consisting of a silane series, an aluminum alkoxide series, a zirconium alkoxide series, and a titanium alkoxide series. Preparing a paste by adding a thermosetting epoxy resin and a curing agent to the quantum dot-oxide composite produced by the method of claim 1;
Applying the paste onto a surface mount LED mold; And
And thermally curing the applied paste. &Lt; Desc / Clms Page number 20 &gt;

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