KR101707100B1 - Quantum dot and poly(3-hexylthiophene) hybrids nanoparticle, and photovoltaic devices including the same - Google Patents

Abstract

The present invention relates to a nanostructure comprising a core layer composed of quantum dots and a shell layer of poly-3-hexylthiophene as a compound of a pi conjugated structure, and a method for producing the same.

Description

TECHNICAL FIELD The present invention relates to a quantum dot-polythiophene hybrid nanostructure and a photovoltaic device including the same,

The present invention relates to a nanostructure in which a polythiophene compound is bonded to a quantum dot and a photovoltaic device comprising the nanostructure.

Semiconductor quantum dots (QDs) are inorganic light-emitting semiconductors. When a quantum dot is made and a light is incident, excitons, which are a pair of electron-holes, become a Bohr radius level and the emission color changes according to the size of the quantum dots. Since the quantum confinement effect is exhibited, a very high luminous efficiency can be observed. Therefore, quantum dots vary in electrical and optical properties such as energy level distribution and emission wavelength depending on their size, and can be applied to electronic devices, displays, and energy devices because they have excellent optical stability when fabricated in the form of a core-shell.

The poly-3-hexylthiophene (P3HT, hereinafter referred to as "P3HT" means "poly-3-hexylthiophene"), which is a pi electron conjugated polymer, is the most efficient conductive polymer used as an active layer in an organic solar cell It is known. This is because P3HT absorbs light to form an exciton which is paired with electron and hole. When this exciton is diffused and it meets an electron acceptor, electrons and holes are separated and electrons move to the cathode. To an active layer that plays an important role in the solar cell mechanism that produces the desired electricity.

The product shape of the hybrid solar cell depends on the manufacturing process: 1) a planar bilayer structure by applying a polymer to the surface of the inorganic material in the plane, 2) a planar bilayer structure in which the inorganic nanoparticles are suspended in the polymer, / Polymer blend structure, 3) an inorganic material in situ formation structure in a polymer by a method of forming a mixture of a polymer and a soluble inorganic material precursor in a film, and 4) a structure of inorganic nanoporous material or nanorod And a vertical nano structure by filling the polymer with a polymer.

Recently, research on hybrid nanowire / nanopillar nanowire grown from Group IV and III-V semiconductors has been underway. These nanostructures have a large surface area at the interface with the organic material and can be processed by various techniques, such as chemical vapor deposition (CVD), laser ablation, molecular beam epitaxy, dry etch . Recently, researches on hybrid solar cells based on Si, GaAs, InP, Ge, nanowires and conjugated polymers (mostly P3HT) have been conducted for the last 2 to 3 years. Another attempt to replace nanowire growth is to utilize nanoporous semiconductors fabricated by electrochemical etching processes. The porous structure formed by the electrochemical etching of Si varies from mesoporous (pore size 5 to 50 nm) to macroporous (pore size hundreds of nm).

On the other hand, hybrid nanostructures in which quantum dots and conjugated polymers (P3HT) form outer layers are not yet known. Therefore, it is expected that the conversion efficiency of the nanostructure bonding the p-type organic compound to the surface of the quantum dot (QD) using a ligand exchange reaction is increased as a solar cell.

Published Patent: 10-2014-0006401

I. L. Medintz et al. Nat. Mater. 4, 435 (2005)

An object of the present invention is to provide a nanostructure in which a pie conjugated molecule having a bulk size is bonded to a quantum dot, a method for producing the same, and a photovoltaic device having improved electrical characteristics using the same.

Quantum dots are zero-dimensional nanomaterials with diameters below tens of nanometers (nm). When quantum dots are formed with inorganic light emitting semiconductors, quantum confinement effect is observed in which the emission color changes depending on the size of the quantum dots. The distribution of the energy level and the characteristics of the emission wavelength are changed depending on the size, and the optical stability is obtained when the core-shell is fabricated. Therefore, semiconductor-based quantum dots can be applied to electronic devices, displays, and energy devices.

On the other hand, a compound having a pi conjugate bond has excellent electric conduction characteristics due to a structure in which electrons in a pi (π) orbit of the constituent carbon atoms are alternately bonded, and exhibits self-luminescence characteristics. As a semiconductor, (organic light emitting device) emitting material. Such a hybrid of a pi conjugated molecule and a quantum dot can be used as a novel material for a light emitting diode in a flexible display device. Hybrid materials with enhanced charge transfer efficiency can also be used as nanoscale photovoltaic devices.

Control of energy transfer and charge transfer efficiency between the quantum dot and the pi conjugated molecule can be done according to the distance between the quantum dot and the pi conjugated molecule and the degree of superposition of the spectrum. Here, the energy transfer refers to a phenomenon in which the energy gap of the light emitting material of a slightly larger material (donor) is transmitted to an acceptor having a smaller energy gap in two emitting molecules. At this time, the overlap of the absorption spectrum of the acceptor with the emission spectrum of the donor should be good, which controls the degree of energy transfer by adjusting the distance between donor and acceptor molecules, and tends to be inversely proportional to the sixth power of distance. That is, in the energy transfer, the limiting distance is 1 to 10 nm, and when the thickness is less than 1 nm, the quenching phenomenon disappears, and when the thickness is more than about 10 nm, the energy transfer is hardly caused.

In addition, charge transfer refers to the phenomenon that the charge of an excited donor is directly transferred to another acceptor when the donor and acceptor molecules are located close to each other, and the electron orbit of the donor and the acceptor It is possible when overlapping, so it occurs when the distance between two substances is very close to 1 nm or less.

The present invention provides a nanostructure using quantum dots as an inner layer (core layer) and a compound of a pi conjugated structure as a shell layer (cell layer), and by controlling the distance between both materials, Provide core material.

The inorganic-organic hybrid nanostructure according to the present invention is a nanostructure having a quantum dot as a semiconductor inorganic material, forming an inner layer (core layer), and a poly-3-hexylthiophene compound (P3HT) as a shell layer , and n-type and p-type semiconductor junctions. Thus, electrons and holes can be transmitted very well, and an excellent effect can be obtained in a device using a photoconductive effect such as a solar cell. Also, the manufacturing method provided by the present invention can be applied to mass production in a way that a nanostructure composed of a core-shell layer can be manufactured easily and quickly.

Figure 1 shows a quantum dot (QD) -poly-3-hexylthiophene (P3HT) hybrid nanostructure.
FIG. 2 shows HR-TEM images of (a) green quantum dot, (b) QD-P3HT-3000 hybrid, (c) QD-P3HT-6000 hybrid and (d) QD-P3HT-10000 hybrid.
(Where 3000, 6000, and 10000 are numbers representing the molecular weight of P3HT, the numbers below have the same meaning)
Figure 3 shows the XRD patterns of P3HT-3000, P3HT-6000 and P3HT-10000.
Figure 4 shows FT-IR spectra of P3HT, QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids.
FIG. 5 shows the results of (a) normalized UV-Vis absorption spectra of QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids and (b) green QD, QD-P3HT- , And QD-P3HT-10000 hybridized product.
6 shows the LCM spectra of green QD, QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids.
FIG. 7 is a conceptual diagram (left) of a conducting atomic force microscope (CAFM) using a single QD-P3HT hybrid and an energy band diagram (left) of a QD-P3HT hybrid .
8 (a), (b) and (c) are AFM surface profiles of the QD-P3HT-3000, QD-P3HT-6000 and QD- (g), (h) and (i) are QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT- 3000, QD-P3HT-6000, and QD-P3HT-10000 hybrid in a full-scale measurement.
FIG. 9 is a graph showing the transient absorption (time-resolved) of QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT- absorption differnce) spectra. (d) shows the time-resolved differnce absorption spectra of QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids after laser pumping at 0.3 ps.
10 (a) shows a time-resolved photoluminescence (trPL) mapping image of green QD, QD-P3HT-3000, QD-P3HT-6000 and QD- Green QD, QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrid materials.

In order to achieve the above object, the present invention provides a nanostructure comprising a core layer made of quantum dots and a shell-layered poly-3-hexylthiophene (P3HT) as a compound having a pi conjugated structure.

QDs can generally be composed of core particles having a core / shell structure and can be provided with ligands bonded to the surface of the core particles. Examples of the core / shell structure of the core particle include II-VI group compound semiconductor nanocrystals such as CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, and HgTe, GaN, GaP, GaAs, InP, InAs III-V group compound semiconductor nanocrystals, or a mixture thereof, and specifically, for example, CdSe / ZnS and the like can be used.

In a specific example of the present invention, the quantum dots constituting the core layer include two kinds of quantum dots selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgSe, HgTe, GaN, GaP, GaAs, InP and InAs ZnS, CdSe / ZnSe, CdS / ZnSe, CdS / ZnS, CdTe / ZnSe and CdTe / ZnS, and more preferably CdSe / ZnS as a core layer .

Also, the ligand formed on the surface of the quantum dots serves to prevent the central particles of the quantum dots from easily aggregating and quenching, and the ligand binds to the center particle to make the center particle hydrophobic. Examples of the ligand include an amine compound or a carboxylic acid compound having an alkyl group having 6 to 30 carbon atoms. Such ligands can be substituted with poly-3-hexylthiophene (P3HT) by a ligand exchange reaction to provide a nanostructure consisting of a core-shell.

As a specific example of the present invention, the poly-3-hexylthiophene has a molecular weight of 3000 to 10,000.

In the present invention, the diameter of the nanostructure may be 17 to 23 nm.

In another specific example of the present invention, a poly-3-hexylthiophene compound as a compound of a pi conjugated structure forming an outer layer is a compound represented by the following formula (1).

≪ Formula 1 >

In the present invention, when n is 10 to 100 in the formula (1), the compound is a preferred nanostructure, and more preferably, n is 15 to 62, which is a nanostructure constituting the outer layer . Wherein X is halogen, preferably F, Cl, Br, I and more preferably Br.

The present invention also provides a method of manufacturing a semiconductor device, comprising the steps of: a) fabricating core-shell quantum dots with two types of inorganic semiconductor material; b) chemically synthesizing poly-3-hexylthiophene as a compound of the pi conjugated bond; c) introducing a functional group at the terminal of said compound; d) introducing the compound into a surface of a quantum dot, wherein the quantum dot and the P3HT compound are composed of a core-shell layer.

Also, in a specific example of the present invention, a method for producing poly-3-hexylthiophene in the step b) is provided, comprising the step of synthesizing a compound represented by the following formula (2).

(2)

In the above formula 2, when n is a compound having a number of from 10 to 100, the present invention provides a preferred nanostructure, and more preferably, a compound having n = 15 to 62, . Wherein X is halogen, preferably F, Cl, Br, I and more preferably Br.

Hereinafter, embodiments of the present invention will be described in detail. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Will be apparent to those of ordinary skill in the art.

Example 1: Synthesis of CdSe-ZnS core-shell Green quantum dot

CdO (0.4 mmol), zinc acetate (4 mmol) and oleic acid (5.5 mL) are added to the reactor together with 1-octadecene (20 mL) and heated to 150 ° C. Oleic acid is substituted for zinc and a vacuum of 100 mTorr is applied for 20 minutes to remove acetic acid, which is an impurity. And when heat of 310 ℃ is applied, it becomes a mixture of transparent color. The one in which Se, S solution dissolving S powder in 0.1 mmol of Se powder and 4 mmol in 3 mL trioctylphosphine after maintained at 310 ℃ 20 minutes to _{Cd (OA) 2, Zn (} OA) reaction containing ₂ solution mechanism Immediately inject. The mixture was grown at 310 ° C for 10 minutes and then stopped by using an ice bath. Ethanol precipitate, and the quantum dots are separated using a centrifuge. The excess impurities are washed off with chloroform and ethanol.

FT-IR (NaCl pellet, cm ^-1 ): 2800-3000 (alkane CH 3), 1617 (C = O)

Example 2: Preparation of nanostructure combining P3HT and QD

The molecular weight of the polymer can be controlled by adjusting the concentration of a certain monomer and the concentration of Ni (dppp) Cl ₂ . 2,5-Dibromo-3-hexylthiophene (3.26 g, 10 mmol) is dissolved in 100 mL of tetrahydrofuran (THF) and stirred under nitrogen gas. A 2M solution of diethyl ether (5.0 mL, 10 mmol) in tert-butylmagnesium chloride is added using a syringe and the mixture is refluxed for 2 h. The oil bath is removed and the reaction mixture is cooled to 23-25 ° C before adding Ni (dppp) Cl ₂ (0.55, 0.37, 0.19 mmol) to anhydrous THF buffer. As the concentration of Ni (dppp) Cl ₂ decreases, the molecular weight (Mw) of allyl-P3HT becomes 3000 Da (Mw = 2.9 x 10 ³ , PDI = 1.14), 6000 (Mw = 6.6 x 10 ³ , PDI = 1.08) (Mw = 9.8 x 10 ³ , PDI = 1.11). The mixture was stirred at room temperature for 15 minutes and a 1 M solution of diethyl ether (4.5 mL, 4.5 mmol) of allylmagnesium bromide was added via syringe. The mixture is further stirred for another 5 minutes and then poured into methanol to precipitate the polymer. The polymer is filtered with a cylindrical filter paper and washed with methanol, hexane and chloroform by soxhlet extraction. The polymer is separated from the chloroform extract.

2,2-Dimethoxy-2-phenylacetophenone (DMPA) and a thiol compound (ethanedithiol) were purchased from Sigma-Aldrich and used without further purification.

Thiol-ene click reaction was used to prepare P3HT with thiol termination. (0.016 g, 0.10 mmol) and allyl-terminated P3HT (0.08 g), 1,2-ethanedithiol (0.8 mL, 9.5 mmol) and 2,2-dimethoxy-2- phenylacetophenone And stirred for 3 hours at room temperature with 365 nm (VIlber Lourmat VL-4 LC) after 3 cycles of freezw pump-thaw cycles. The light source is 4W. The reaction mixture was precipitated with methanol and quantitatively the allyl end group was converted to the thiol functional group by ¹ H NMR.

Oleic acid-stabilized CdSe / ZnS quantum dots (5 mg) and P3HT (50 mg) in the terminal group of the thiol group were dispersed in 5 mL of chloroform and 5 mL of ethanol and ultrasonicated for 3 hours. 40 mL of chloroform was added to the mixture to precipitate 11-mercapto-1-undecanol-capped CdSe / ZnS quantum dots (QD). FIG. 1 is a cross-sectional view of a quantum dot-P3HT hybrid nanostructure produced by the above method.

[Test Example and Analysis]

As shown in FIG. 2A, in a high-resolution transmission electron microscope (HR-TEM) image of the CdSe / ZnS quantum dots, the diameter of each QD was measured to be 8 ± 2 nm. QD-P3HT-3000 hybrid, (c) QD-P3HT-6000 hybrid and (d) QD-P3HT-10000 hybrid were measured as 18 ± 1, 20 ± 1 and 22 ± 1 nm, respectively. As the molecular weight of P3HT increased, the size of QD-P3HT hybrid increased slightly.

XRD patterns of P3HT functionalized with thiol groups with various molecular weights were measured in order of polymer chain (see FIG. 3). The crystal sizes of QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 were measured to be 8.4, 9.5 and 9.7 nm, respectively. As the molecular weight of P3HT increased, the size of crystals increased.

FT-IR spectra show that a peak at 727 cm ^-1 represents the methyl rock of the hexyl group and 827 cm ^-1 and 889 cm ^-1 represent the CH manding of the thiophene ring and the CH 3 terminal locking rocking, indicating that P3HT is present in QD-P3HT hybrids (see FIG. 4).

In normalized UV-Vis absorption spectra, the P3HT-pi (pi) ^* transition peak in QD-P3HT-3000 hybrids appeared at about 433 nm. The pi-pi ^* transition peak was moved when the QD-P3HT-6000 and QD-P3HT-10000 to 454 nm and 480 nm respectively, to the long wavelength side. The long-wavelength shift of this pi-pi ^* transition peak is due to the elongated planar structure of P3HT. As the molecular weight of P3HT increases in the hybrid, the UV-Vis absorption spectrum of QD-P3HT hybrids widens the absorption width more and additionally the peaks are observed at 563 nm and 603 nm. This is due to the enhanced internal-chain interaction of P3HT in the shell layer of the hybrid. This result indicates that the internal-chain interaction of the P3HT chain of the QD-P3HT-10000 hybrid is stronger than the other (see Fig. 5 (a)).

Normalized solution PL spectra reveal a PL peak of QD at 530 nm, which means green emission. The main peak of the QD-P3HT hybrid appears at about 580 nm. The line width and shoulder peak of the QD-P3HT hybrid were different depending on the molecular weight of P3HT. The PL shoulder peak at about 630 nm in the Qd-P3HT-6000 and QD-P3HT-10000 hybrids is due to the enhanced internal-chain interaction of the P3HT main chain. The PL and optical absorption peaks in QD-P3HT-10000 are clearly distinguished. The PL spectrum of the QD-P3HT-3000 hybrid has the broadest peak. QD-P3HT-6000, QD-P3HT-6000, QD-P3HT-6000 and QD-P3HT-6000 as shown in FIG. 5 (b) At 10000, energy / charge transfer is more efficient.

6 showing the LCM spectra of the green QD, QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids, PL intensity decreases as the molecular weight of P3HT increases, It is judged that fluorescence is extinguished by forming an emitter by the interaction of pi - pi between the chains. At 600-700 nm, a weak shoulder PL peak is measured in the QD-P3HT hybrid because of the excimer formation of P3HT. From these results, it can be seen that efficient charge transfer from QD to P3HT is achieved.

To measure the photovoltaic properties of the QD-P3HT hybrids, they were measured by an atomic force microscope (CAFM) (see FIG. 7). The QD-P3HT-10000 hybrid was found to have more efficient and faster charge transfer between p-type P3HT and quantum dots (QD) due to the well-aligned P3HT chains and strong internal-chain interactions due to their high molecular weight 8 to 10). In addition, QD-P3HT-3000, QD-P6000 and QD-P3HT-10000 hybrids increased the solar cell efficiency (PCE) by 0.10%, 0.16% and 0.22%, respectively, with increasing chain length of P3HT. This shows that the transfer shift between P-type P3HT and QD increases with increasing molecular weight.

The transient absorption (time-resolved absorption differnce) spectra results show whether the charge transfer between the quantum dots and P3HT is successful. In the green QD of the QD-P3HT absorbing the 510 nm laser, The charge is delivered to the P3HT within a few picoseconds (ps). A negative band corresponding to the attenuation of the charge movement due to the absorption of the bottom state of the hybrid body can be seen. QD-P3HT-10000 was slower than QD-P3HT-6000 with curve attenuation between wavelengths of 550-600 nm. This shows that QD-P3HT-6000 and QD-P3HT-10000 exhibit negative peaks at 550 nm of charge transfer efficiency from QD to P3HT-10000 demonstrate the absorption of the bottom states of the QDs because they are very well hybridized with QD-P3HT- (See FIG. 9).

10 (a) shows a time-resolved photoluminescence (trPL) mapping image of green QD, QD-P3HT-3000, QD-P3HT-6000 and QD-P3HT-10000 hybrids, This is to look at the life of the exciton. The quantum dots showed the brightest red foot and characteristics, indicating a relatively long exciton lifetime. On the other hand, QD-P3HT-10000 is the darkest, which means short acid life. The larger the molecular weight of P3HT, the darker the trPL mapping image.

Claims (15)

A core layer made of quantum dots;
Poly-3-hexylthiophene (P3HT) as a compound of a pi conjugated structure is a shell layer;
In the nanostructure,
Wherein the nanostructure is represented by the following formula (1)
≪ Formula 1 >

(In the above formula 1, n is from 10 to 100 and X represents halogen.)
The quantum dot of claim 1, wherein the quantum dot is a combination of two selected from the group consisting of CdS, CdSe, CdTe, ZnS, ZnSe, ZnTe, HgS, HgTe, GaN, GaP, GaAs, InP, Nano structure
3. The nanostructure according to claim 2, wherein the quantum dot is selected from the group consisting of CdSe / ZnS, CdSe / ZnSe, CdS / ZnSe, CdS / ZnS, CdTe / ZnSe,
2. The nanostructure according to claim 1, wherein the poly-3-hexylthiophene has a molecular weight (Mw) of 3000 to 10,000.
2. The nanostructure according to claim 1, wherein the nanostructure has a diameter of 17 to 23 nm delete delete 2. The nanostructure according to claim 1, wherein in the formula 1, n is from 15 to 62, 2. The nanostructure according to claim 1, wherein X in the formula (1) is Br. a) fabricating core-shell quantum dots with two inorganic semiconductor materials;
b) chemically synthesizing poly-3-hexylthiophene (P3HT) as a compound of the pi conjugated bond;
c) introducing a functional group at the terminal of said compound;
d) introducing the compound into the surface of the quantum dot;
(3), wherein the step (d) comprises introducing a compound represented by the following formula (2) into a core-shell layer of a nanocomposite comprising a quantum dot and a poly-3-hexylthiophene .
(2)

(In the above formula 2, n is from 10 to 100, and X is halogen)
delete The method according to claim 10, wherein the step d) is a step of introducing a compound to the surface of a quantum dot by a ligand exchange reaction
The method according to claim 10, wherein in the formula 2, n is from 15 to 62 and X is Br.
A photovoltaic device comprising a nanostructure according to any one of claims 1 to 5 and 9 to 9 between a first pole and a second pole. An electronic device comprising a photovoltaic device comprising a nanostructure according to any one of claims 1 to 5 and 8 to 9

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