KR102657404B1 - Perovskite core-shell quantum dot and its manufacturing method - Google Patents

Abstract

Quantum dots with a core-shell structure according to an embodiment of the present invention include a core layer with a perovskite structure; and a shell layer including a Si-0-Si bond, wherein the shell layer is bonded to a C1-C6 alkyl group, a C1-C6 alkenyl group, or a C1-C6 alkynyl group.

Description

Perovskite core-shell quantum dot and its manufacturing method {Perovskite core-shell quantum dot and its manufacturing method}

The present invention relates to perovskite core-shell quantum dots based on hydrophobic silane ligands.

Recently, organometallic halide perovskite materials are promising semiconductor materials as ideal materials for high-performance lighting and display systems due to their advantages of simple color adjustment and high absorption coefficient. Accordingly, research on various processes and new materials to synthesize the core-shell structure that encapsulates the core of quantum dots is being reported.

Conventionally, research was conducted on quantum dots using perovskite materials to improve stability and durability by silanizing the outside of the core. In order to synthesize a shell of silica material outside the core, hydrolysis and condensation reaction processes are required, and during this process, most silane ligands have dispersibility problems due to aggregation problems. This causes the shell to easily disintegrate and affect the core during long-term stability tests.

Ligands such as TMOS, TEOS, and APTMS, which are mainly used in core-shell quantum dot synthesis, have problems with water being generated during the synthesis process and quantum dots aggregating. In addition, polar solvent and base conditions are required to form the silica shell structure, but there is a fatal disadvantage that perovskite materials decompose under these synthesis conditions.

U.S. published patent 2020-0385632 A1

The present invention seeks to provide perovskite-based core-shell quantum dots with improved stability and dispersibility.

In addition, the present invention seeks to provide perovskite-based core-shell quantum dots with improved photoluminescence quantum yield (PLQY).

In addition, the present invention seeks to provide perovskite-based core-shell quantum dots manufactured through a one-pot process design that does not require base conditions and ligand exchange treatment.

In order to solve the above problem, quantum dots of the core-shell structure according to an embodiment of the present invention include a core layer of a perovskite structure; and a shell layer including a Si-0-Si bond, wherein a C1-C6 alkyl group, a C1-C6 alkenyl group, or a C1-C6 alkynyl group is bonded to a Si element in the shell layer.

Additionally, as an example, the core layer of the perovskite structure may be represented by the following formula (1).

[Formula 1]

ABX _{3- n}

(In Formula 1, A is at least one selected from organic ammonium, organic amidinium, and alkali metal, and B is a divalent transition metal, rare earth metal, alkaline earth metal, Pb, Sn, Ge, Ga, In , Al, Sb, Bi, Po and at least one selected from organic materials, and X and It is at least one selected from F, Cl, Br and I, and 0 ≤ n ≤ 3.)

Additionally, as an example, one C1-C6 alkyl group, C1-C6 alkenyl group, or C1-C6 alkynyl group may be bonded to the Si element in the shell layer.

One embodiment of the present invention forms a shell layer on the core of the perovskite structure using a silane ligand represented by the following formula (2), wherein the Si element contains one C1-C6 alkyl group, C1-C6 alkenyl group, or C1- A C6 alkynyl group can be combined. By controlling the ligand length and the number of alkyl groups, perovskite-based core-shell structured quantum dots have significantly improved stability and dispersibility even under polar conditions and significantly improved photoluminescence quantum yield. can be manufactured.

[Formula 2]

(In Formula 2, R1 to R3 are each independently a C1-C6 alkyl group, C1-C6 alkenyl group, or C1-C6 alkynyl group)

Methoxy or ethoxy groups react with solvents or external moisture to produce methanol or ethanol, and silanization of the siloxane bond of Si-O-Si occurs through a dehydration condensation reaction. This causes the formation of a network structure between silane ligands and aggregation between quantum dots, causing precipitation of core-shell quantum dots. Accordingly, to suppress precipitation, a shell layer was designed in which methoxy and ethoxy groups were replaced with a single alkyl group. In addition, perovskite-based core-shell quantum dots were successfully formed through the reprecipitation technology through ligand separation of the present invention.

Additionally, as a most preferred example, one methyl group (-CH ₃ ) may be bonded to the Si element in the shell layer. This can be formed by using 3-aminopropyl(diethoxy)methylsilane (APDEMS) as the first ligand in the process described later.

As a result, perovskite-based core-shell quantum dots with significantly improved dispersibility and stability can be manufactured without base conditions through the one-pot process described below.

Additionally, as an example, the quantum dots of the core-shell structure may have a photoluminescence quantum yield (PLQY) of 95% or more, more preferably 96% or more.

Additionally, as an example, the quantum dots of the core-shell structure may have peaks at positions of 1040 to 1060 cm ^-1 and 1258 to 1260 cm ^-1 , respectively, as a result of Fourier transform infrared spectroscopy (FT-IR) analysis.

Additionally, as an example, the perovskite-based core-shell quantum dot particles may be doped nanoparticles in which A, B, and X are replaced with different elements.

In the present invention, different ligands are separated and reacted in different solvents, and quantum dots with a perovskite-based core-shell structure with improved solution stability can be manufactured through optimized redispersion and reprecipitation techniques. Unlike existing precipitation technologies, the present invention can stably precipitate quantum dot particles with a perovskite-based core-shell structure and efficiently remove residual substances such as unreacted precursors and polar solvents through a process of removing the supernatant. there is. The manufacturing method will be described below.

The method of manufacturing quantum dots with a core-shell structure according to an embodiment of the present invention involves preparing a precursor solution by stirring a first halogen compound, a second halogen compound, and a first ligand represented by the following formula (2) in a first solvent. step; Preparing a non-solvent by stirring a compound containing a second ligand different from the first ligand in a second solvent; Stirring the precursor solution and the non-solvent; and obtaining a precipitate by first centrifuging the stirred solution; Includes.

[Formula 2]

(In Formula 2, R1 to R3 are each independently a C1-C6 alkyl group, C1-C6 alkenyl group, or C1-C6 alkynyl group)

First, a step of preparing a precursor solution is performed by stirring the first halogen compound, the second halogen compound, and the first ligand represented by Formula 2 in a first solvent.

As an example, the first halogen particle may be one or more selected from organic ammonium halide, organic amidinium halide, and alkali metal halide.

As an example, the first halogen compound may be included in the first solvent at a concentration of 0.05 to 0.2 mol/L, or 0.1 to 0.15 mol/L. In this way, by optimizing the concentration of the precursor, more stable perovskite nanoparticles can be manufactured.

As an example, the second halogen particle may be represented by BX ₂ as a reactant for forming the core layer of the perovskite structure represented by Formula 1, and may be PbBr 2 , SnCl ₂ , or GeCl ₂ as an example. there is.

Additionally, as described above, as a most preferred example, the first ligand may be 3-aminopropyl(diethoxy)methylsilane.

Next, a step of preparing a non-solvent is performed by stirring a compound containing a second ligand different from the first ligand in a second solvent.

As an example, the second ligand is different from the first ligand and may be independently selected from amine, carboxylic acid, silane, phosphine, phosphine oxide, phosphonic acid, phosphinic acid, and thiol. As a more preferred example, the second ligand may be carboxylic acid. Carboxylic acid acts on the precipitation and removal process of aggregated quantum dots to control the polarity of the nucleation environment and at the same time can be used as a stabilizer. As a most preferred example, the second ligand may be oleic acid.

Oleic acid acts on the precipitation and removal process of aggregated quantum dots to control the polarity of the nucleation environment and can be used as a stabilizer at the same time. In particular, when optimizing the amount of oleic acid added, oleic acid suppresses aggregation of quantum dots, stabilizes the solution, and induces precipitation rather than co-ligand. Therefore, solution dispersibility can be improved.

The second ligand may be included in an amount of 10 to 60% by volume, 20 to 50% by volume, or 20 to 40% by volume based on the volume of the second solvent. If the oleic acid is less than the above range, there may be a problem in which precipitation of quantum dot particles is difficult, and if the oleic acid is above the above range, there may be a problem in that the size distribution of quantum dot particles becomes wider.

As an example, the second solvent may include toluene, hexane, cyclohexane, chloroform, xylene, octane, chloroethylene, chlorobenzene, or mixtures thereof.

Next, a step of stirring the precursor solution and the non-solvent is performed.

When the precursor solution and the non-solvent are stirred, perovskite-based core-shell quantum dot particles are formed and a specific color may appear.

Next, a step of first centrifuging the stirred solution to obtain a precipitate is performed. In this step, the first centrifugation may be performed at 1000 to 10000 rpm or 3000 to 8000 rpm. If the first centrifugation speed is outside the above range, there may be a problem in which it is difficult for quantum dot particles to settle. The present invention can produce quantum dot particles with improved dispersibility and stability by optimizing the centrifugation speed.

Next, after obtaining the precipitate containing the quantum dot particles, a step of dispersing it in a third solvent may be further performed. The dispersion step is a step of obtaining a high-concentration dispersion by redispersing the precipitate in a third solvent. The third solvent may be a non-polar solvent capable of stably dispersing perovskite-based core-shell quantum dot particles in a colloidal state. .

As an example, the third solvent may include hexane, toluene, cyclohexane, chloroform, xylene, octane, chloroethylene, chlorobenzene, or mixtures thereof. By carrying out this stable redispersion step, residual precursors such as ligands and polar solvents can be removed, making it possible to manufacture quantum dot particles with guaranteed stability as a colloidal solution. Since the production method according to the embodiment of the present invention does not undergo precipitation and purification processes using a polar solvent, solution stability can be ensured. More preferably, toluene can be used, and the role of oleic acid, which can act as a good stabilizer due to charge balance, can be maximized.

Next, a second centrifugation step may be performed on the dispersed solution for further purification.

An optoelectronic device according to an embodiment of the present invention includes a first electrode; second electrode; and a light-emitting layer, a photoactive layer, or an intermediate layer located between the first electrode and the second electrode and including the quantum dots of the core-shell structure of claim 1.

As an example, the optoelectronic device may be a solar cell, light emitting device, photo detector, photo transistor, memory device, etc.

As an example, the first electrode and the second electrode may be a cathode or an anode, and there is no particular limitation as they are electrodes commonly used in optoelectronic devices.

Perovskite-based core-shell quantum dots according to embodiments of the present invention have significantly improved thermal stability and dispersibility.

In addition, perovskite-based core-shell quantum dots according to embodiments of the present invention have significantly improved photoluminescence quantum yield (PLQY).

In addition, perovskite-based core-shell quantum dots according to an embodiment of the present invention can be manufactured through a one-pot process design that does not require base conditions and ligand exchange treatment.

Figure 1 shows (a) a schematic diagram of a core-shell quantum dot using a perovskite-based APDEMS ligand, (b) a comparison of the APTMS chemical structure, and (c) the APDMES chemical structure.
Figure 2 compares Fourier transform infrared spectroscopy (FT-IR) analysis results.
Figure 3 shows red, green, and blue core-shell quantum dot (a) image (b) absorbance (c) photoluminescence spectrum using APDMES ligand.
Figure 4 is a TEM image of red, green, and blue core-shell quantum dots using APDMES ligand.
Figure 5 compares (a) the image and intensity of luminescence in a polar environment, (b) the rate of change in intensity of luminescence over time, and (c) images after 0 hours, 12 hours, and 100 hours in a 60 ˚C environment.
Figure 6 shows solution images of core shell quantum dots using APTMS and APDEMS after (a) 0 hours, 6 hours, and 30 hours, (b) APTMS core shell dispersion data using TurbiScan, (c) APDMES core shell using TurbiScan. Comparison of dispersibility data, (d) dispersibility measurement principle, and (e) Turviscan stability data over time.

Hereinafter, the present invention will be described in more detail through examples. Since these examples are merely for illustrating the present invention, the scope of the present invention is not to be construed as limited by these examples.

Expressions such as “comprising” used in this specification are understood as open-ended terms that imply the possibility of including other embodiments, unless specifically stated otherwise in the phrase or sentence containing the expression. It has to be.

As used herein, “preferred” and “preferably” refer to embodiments of the invention that may provide certain advantages under certain circumstances. However, under the same or different circumstances, other embodiments may also be preferred. Additionally, mention of one or more preferred embodiments does not mean that other embodiments are not useful, nor is it intended to exclude other embodiments from the scope of the invention.

[Preparation of reagents]

CH ₃ NH ₃ I (MAI, 99.99%, TCI Co., Ltd.), CH ₃ NH ₃ Br (MABr, 99.99%, TCI Co., Ltd.), PbI ₂ (99.99%, TCI. Co., Ltd. .), PbBr ₂ (99.99%, TCI Co., Ltd.), n-octylamine (99%, Sigma-Aldrich), APTMS (97%, Sigma-Aldrich), APDEMS (97%, Sigma-Aldrich), OA (90%, Sigma-Aldrich), DMF (99.9%, Sigma-Aldrich), acetonitrile (99.8%, Sigma-Aldrich), toluene (99.8%, Sigma-Aldrich), n-hexane (95%, Sigma-Aldrich) , and acetone (99.5%, SAMCHUN) were prepared,

[Example] Silica core-shell MAPbX using APDEMS ligand ₃ -SiO ₂ (X = Br, I) Manufacturing of quantum dots

Example 1 : Preparation of silica core shell MAPbBr ₃ -SiO ₂ quantum dot - green light emission

MABr (0.1 mmol), PbBr ₂ (0.1 mmol), and APDEMS (15 μL) were dissolved in DMF (1 mL) by sonication to obtain a transparent precursor solution.

Next, the precursor solution was quickly added to an environment where toluene (5 mL) and oleic acid (1.7 mL) were being stirred. By stirring the mixture for 1 hour, the silica precursor underwent hydrolysis and condensation reactions.

The mixture was then centrifuged at 3000 rpm for 10 minutes to obtain a precipitate containing larger aggregated silica core-shell MAPbBr ₃ -SiO ₂ particles.

Next, the supernatant containing impurities and other ions was discarded, and the remaining precipitate was redispersed in n-hexane (2 mL) and purified.

Example 2 : Preparation of silica core shell MAPbI ₃ -SiO ₂ quantum dot - red light emission

The same procedure as Example 1 was performed, except that MAI (0.1 mmol), PbI ₂ (0.1 mmol), and APDEMS (30 μL) were dissolved in acetonitrile (1 mL) through sonication.

Example 3 : Preparation of silica core shell MAPbBr ₃ -SiO ₂ quantum dot - blue light emission

The same procedure as Example 1 was performed except that 60 μL of APDEMS was used.

[Comparative Example 1] Preparation of bare-quantum dots using octylamine ligand

MABr (0.1 mmol), PbBr ₂ (0.1 mmol), and n-octylamine (15 μL) were dissolved in DMF (1 mL) by sonication to obtain a transparent precursor solution.

Next, the precursor solution was quickly added to an environment where toluene (5 mL) and oleic acid (1.7 mL) were being stirred. In the meantime, the solution gradually turned greenish yellow.

The mixture was then centrifuged at 8000 rpm for 5 minutes to obtain a larger aggregated precipitate.

Next, the supernatant containing impurities and other ions was discarded, and the remaining precipitate was redispersed in n-hexane (2 mL) and purified.

[Comparative Example 2] Silica core-shell MAPbX using APTMS ligand ₃ -SiO ₂ (X = Br, I) Manufacturing of quantum dots

The same procedure as Example 1 was carried out, except that 3-Aminopropyl(triethoxy)silane (APTMS) ligand was used.

[Experimental Example 1]

Silica core-shell quantum dots using APDEMS ligand as a silica precursor were successfully synthesized through a one-pot synthesis method based on S-LMRP technology.

Additionally, the mixture was stirred for a sufficient time to successfully cross-link the silica precursor through hydrolysis and condensation reactions.

When using the APDEMS ligand, the process of forming a silica shell layer through cross-linking can be expressed in Scheme 1 below. According to the following reaction formula, the silica shell layer is formed by Si-O-Si bonding.

[Scheme 1]

According to Figure 1, core-shell quantum dots using APTMS ligand have -OCH ₃ groups before hydrolysis and condensation reactions occur. However, since APDEMS has -CH3 groups in addition to -0CH3 groups, the aggregation problem of core-shell particles can be resolved as a result.

According to the Fourier transform infrared spectroscopy (FT-IR) analysis results of FIG. 2, it can be confirmed that core-shell quantum dots using APDEMS ligand have peaks around 1050 cm ^-1 and 1259 cm ^-1 .

Figure 3(a) shows a quantum dot optical image in 365nm UV lamp ambient light. As can be seen in Figures 3 (b) and (c), the range of absorption and PL spectrum is adjusted to a value of 468.4 to 705.4 nm, depending on the amount of APDEMS.

Table 1 below shows each measured value according to the concentration of silane in core-shell quantum dots using APDEMS ligand.

[Table 1]

According to the TEM image of FIG. 4, it was confirmed that the interplanar distances of the quantum dots according to each example were 2.92, 3.17, and 2.96 Å, respectively.

[Experimental Example 2] Stability evaluation

Perovskite quantum dots have very poor stability when exposed to polarity, heat, and light sources. To solve the above problem, the quantum dots according to the examples and comparative examples were dispersed in acetone, a polar solvent.

According to Figure 5(a), most of the bare-quantum dots suspended in acetone decomposed and the suspension turned transparent, but the core-shell quantum dots using APDEMS ligands decomposed less and maintained luminescence.

In addition, it can be seen that the PL intensity of core-shell quantum dots using the APDEMS ligand is significantly higher than that of the case using the APTMS ligand. The decrease in PL strength is due to lower stability in a polar environment, and this is because the hydroxyl group of APTMS interacts with acetone and the shell layer easily ruptures. On the other hand, when the APDEMS ligand is used, it can have excellent stability even in a polar environment because most of the shell layer is protected by methyl groups.

According to Figure 5(b), it can be seen that the PL of core-shell quantum dots using APTMS ligands significantly decreases at 60°C, while the luminescence of core-shell quantum dots using APDEMS ligands is almost maintained. Additionally, after 500 hours at 60°C, the bare-quantum dots were almost decomposed and did not emit light, and the PL intensity of core-shell quantum dots using APTMS ligands was 34.5%, and the PL intensity of core-shell quantum dots using APDEMS ligands was 34.5%. It can be seen that the strength is maintained at 70%. The presence of an outer shell improves thermal stability, since the use of APTMS ligands is more affected when the shell layer collapses due to aggregation.

According to the thin film image of each quantum dot in Figure 5(c), it can be seen that the release of heavy metal ions within the perovskite core is suppressed when the APDEMS ligand is used.

[Experimental Example 3] Dispersibility evaluation

The dispersibility of each quantum dot was analyzed through TurbiScan analysis. The analysis principle is to measure the amount of light reflected from the device at an angle of 45° due to collisions between the emitted laser and the opaque particles (see Figure 6(d)).

According to Figure 6(a), when APTMS ligand was used, the particles settled quickly and the suspension became transparent after 30 hours. This is because the sedimentation rate changes due to agglomeration of particles during the synthesis process. In contrast, when the APDEMS ligand was used, it remained opaque even after 30 hours, which was due to the low sedimentation rate due to excellent dispersibility.

According to Figures 6(b) and (c), it can be seen that when the APTMS ligand was used, the sedimentation rate was 2% faster than when the APDEMS ligand was used.

To confirm the dispersion stability of each quantum dot, the Turviscan Stability Index (TSI) was calculated by measuring various degrees of light scattering for 2 hours. As dispersibility decreases, the TSI value increases. According to Figure 6(e), it can be seen that the TSI value of core-shell quantum dots using APDEMS ligand increases slowly.

Claims (13)

delete delete delete delete delete delete Core layer of perovskite structure; and
In the method of manufacturing quantum dots of a core-shell structure including a shell layer containing Si-0-Si bonds,
Preparing a precursor solution by stirring a first halogen compound, a second halogen compound, and a first ligand represented by the following formula (2) in a first solvent;
Preparing a non-solvent by stirring a compound containing a second ligand different from the first ligand in a second solvent;
Stirring the precursor solution and the non-solvent; and
Obtaining a precipitate by first centrifuging the stirred solution; Including,
Quantum dot manufacturing method with core-shell structure:
[Formula 2]

(In Formula 2, R1 to R3 are each independently a C1-C6 alkyl group, a C1-C6 alkenyl group, or a C1-C6 alkynyl group).
According to claim 7,
The first ligand is 3-aminopropyl(diethoxy)methylsilane,
Quantum dot manufacturing method with core-shell structure.
According to claim 7,
The second ligand is oleic acid,
Quantum dot manufacturing method with core-shell structure.
According to claim 7,
The first solvent is a polar solvent and includes dimethylformamide (DMF), dimethyl sulfoxide (DMSO), acetonitrile, formamide, ethanolamine, isopropyl alcohol, GBL, or mixtures thereof.
Quantum dot manufacturing method with core-shell structure.
According to claim 7,
The second solvent includes toluene, hexane, cyclohexane, chloroform, xylene, octane, chloroethylene, chlorobenzene, or mixtures thereof.
Quantum dot manufacturing method with core-shell structure.



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