KR101690191B1 - Graphene-quantum layered heterostructure and manufacturing method thereof, and solar cell by using the same - Google Patents
Graphene-quantum layered heterostructure and manufacturing method thereof, and solar cell by using the same Download PDFInfo
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Abstract
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphene-quantum dot nanocomposite structure, a method of manufacturing the same, and a solar cell including the graphene-quantum dot nanocomposite structure. More particularly, the present invention relates to a nanocomposite structure including a plurality of graphene layers and a quantum dot layer, A composite structure, a manufacturing method thereof, and a solar cell including the same.
According to the present invention, it is possible to uniformly form quantum dots to suppress exciton recombination in the quantum dots, to induce photoelectric transfer smoothly, and to manufacture a solar cell having high efficiency.
Description
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphene-quantum dot nanocomposite structure, a method of manufacturing the same, and a solar cell including the graphene-quantum dot nanocomposite structure. More particularly, the present invention relates to a nanocomposite structure including a plurality of graphene layers and a quantum dot layer, A composite structure, a manufacturing method thereof, and a solar cell including the same.
Generally, a zero-dimensional semiconductor quantum dot having a size of several nanometers (nm) is spatially limited by the quantum confinement effect in all directions, so that excitons formed through light energy are spatially limited. Thus, unlike conventional bulk materials, / Electrical properties. In addition, since it has a high extinction coefficient and can absorb light of a desired wavelength according to size control, development of various semiconductor quantum dots and energy conversion devices using the semiconductor quantum dots have been actively conducted worldwide.
In particular, solar cells based on semiconductor quantum dots are attracting attention as next generation energy conversion materials and application fields because they can overcome the theoretical efficiency limit of existing solar cells by utilizing unique optical / electrical characteristics.
However, until now, there have been various difficulties in the development of a quantum dot solar cell, so that a high efficiency solar cell is not realized. One of these technical difficulties is that effective electron transfer and extraction are not achieved due to chemical and structural defects within the quantum dots.
That is, the conventional technique has a problem that it is difficult to chemically dope with very small quantum dots mixed with the conductive material, and it is difficult for the quantum dots formed by the conductive material to be uniformly distributed and also the aggregation of the quantum dots by the conductive material (Patent Document 1)
In addition, the quantum dots are difficult to be uniformly distributed even in the case of a composite in which quantum dots and graphene are covalently bonded, and it is difficult to realize a solar cell having high efficiency by substantially applying the composite. (Patent Document 2)
Accordingly, there is a need to develop a method for solving the above-described problems and capable of efficiently maximizing photoelectron transfer by suppressing recombination of excitons in quantum dots.
SUMMARY OF THE INVENTION It is an object of the present invention to provide a nanocomposite structure including a graphene layer and a quantum dot layer capable of suppressing recombination of excitons and efficiently improving photoelectrons movement in the quantum dots, A method for producing the same, and a solar cell including the same.
In order to achieve the object of the present invention, the present invention provides a nanocomposite structure comprising (a) a graphene layer and (b) a quantum dot layer,
The graphene layer (a) is interposed between a plurality of (b) quantum dot layers,
Wherein the graphene layer (a) is formed as an m-layer, and the (b) quantum dot layer is formed as an n-layer. (Where 0 < m? 20, 1 < n? 20, m, n = integer)
And n is 3 to 10.
And the total thickness of the quantum dot layer is 50 to 400 nm.
The quantum dot includes at least one selected from the group consisting of CdSe, ZnS, ZnSe, CdTe, CdS, GaN, GaP, InP and GaAs.
And the total thickness of the graphene layer is 0.3 to 7 nm.
The present invention also provides a method for producing a quantum dot layer, which comprises (A) forming a quantum dot layer, (B) forming a graphene layer on the quantum dot layer, and (C) forming a quantum dot layer on the graphene layer And a method for producing the nanocomposite structure.
The steps (B) and (C) are repeatedly performed,
Wherein the graphene layer is formed of m layers and the quantum dot layer is formed of n layers.
The step (B) is characterized in that a graphene layer is formed by at least one method selected from spin coating, doctor blade, and spray.
The step (C) is characterized in that a quantum dot layer is formed by at least one method selected from spin coating, doctor blade, and spray.
The concentration of the graphene is 1 to 50 mg / mL.
The present invention also provides a solar cell comprising the nanocomposite structure.
According to the present invention, by forming a plurality of graphene layers and quantum dot layers and fabricating a nanocomposite structure, conventionally, quantum dots of very small size are mixed with a conductive material, which makes it difficult to perform chemical doping and unevenness or aggregation of quantum dots The problem can be solved.
In addition, it is possible to suppress exciton recombination in the quantum dots and to induce the photoelectric transfer in the graphene layer smoothly, thus making it possible to apply the present invention to a solar cell having high efficiency.
1 is a cross-sectional view illustrating a nanocomposite structure according to an embodiment of the present invention.
2 is a cross-sectional view showing the solar cell of Example 1. Fig.
3 is a cross-sectional view showing the solar cell of Example 2. Fig.
FIG. 4A is a schematic diagram showing the process of Example 1, and FIG. 4B is a schematic view showing a state in which electrons in the graphene layer constituting the nanocomposite structure of Example 1 are transferred from LUMO (Lowest Unoccupied Molecular Orbital) to HOMO Molecular Orbital). ≪ / RTI >
FIG. 5 shows the results of an analysis of the surface and crystal structure of the quantum dot layer and the graphene layer of Example 1, wherein (a) shows the measurement of the surface of the quantum dot layer by transmission electron microscopy (TEM) (B) is a graph showing X-ray diffraction (XRD) analysis results for the quantum dot layer, and (c) is a graph showing the surface of the graphene layer by scanning electron microscopy (D) is a graph showing the results of Raman spectroscopy measurement of the graphene layer of Example 1. Fig.
FIG. 6A is a graph showing the results of measurement of current density / voltage for the solar cells of Examples 1 and 2 and Comparative Example 1. FIG. 6B is a graph showing the results of measurement of the current density / voltage of the solar cells of Examples 1 and 2 and Comparative Example 1. FIG. (Jsc) and power conversion efficiency (PCE) for the solar cells of Examples 1 and 2 and Comparative Example 1, Fig.
7 (a) and 7 (b) are graphs showing the results of measurement of the photocurrent and photoreaction rates of the solar cells of Example 2 and Comparative Example 1. FIG. 7 (b) It is a graph.
Hereinafter, various aspects and various embodiments of the present invention will be described in more detail.
The present invention relates to a nanocomposite structure comprising a plurality of graphene layers and a quantum dot layer to improve the movement of photoelectrons, a method of manufacturing the nanocomposite structure, and a solar cell including the nanocomposite structure.
In order to improve the movement of photoelectrons as described above, the present invention is formed by a nanocomposite structure comprising (a) a graphene layer and (b) a quantum dot layer, wherein the graphene layer (a) And the quantum dot layer is interposed between the quantum dot layers, wherein (a) the graphene layer is formed as an m-layer, and (b) the quantum dot layer is formed as an n-layer. (Where 0 < m? 20, 1 < n? 20, m, n = integer)
In the nanocomposite structure according to the present invention, the (a) graphene layer is formed of m layers, and the (b) quantum dot layer is formed of n layers, and m is preferably 0 to 20. When m is less than 1 It does not include a graphene layer which is a conductive material, or a plurality of quantum dot layers can not be formed, so that it is difficult to move the photoelectrons. When m or n is more than 20, it is not preferable because short-circuiting of the device or increase of recombination of photo-generated charge carriers is worried.
The thickness of the quantum dot layer is preferably 50 to 400 nm. If the thickness is less than 50 nm, it is undesirable because a decrease in the light absorption rate of the quantum dot is likely to occur. When the thickness is more than 400 nm, And thus the efficiency is lowered.
It is preferable that each layer of the quantum dot layer is in the range of 5 to 40 nm, which is a range for efficiently transferring the photoelectrons to the graphene layer, and is outside the above range, .
The quantum dot preferably includes at least one selected from the group consisting of CdSe, ZnS, ZnSe, CdTe, CdS, GaN, GaP, InP, and GaAs, but is not limited thereto.
The graphene layer exhibits excellent conductivity and can effectively induce separation or migration before the recombination of the quantum dots and the electrons transferred into the semiconductor. This phenomenon increases the amount of electrons transferred to increase the short circuit current density And energy conversion efficiency.
The total thickness of the graphene layer is preferably 0.3 to 7 nm, and more preferably, the thickness of the graphene layer is 0.3 to 0.4 nm. If the thickness exceeds 7 nm, there is a problem of device short circuit or increase of recombination of photo-generated charge carriers.
In addition, the graphene has a diameter of 150 to 3000 nm, more preferably 500 nm in average, which can be controlled with the graphene concentration, And it was confirmed that the electrical characteristics were the most excellent.
In this regard, referring to FIG. 7, which shows the result of measurement of photocurrent and photoreaction rate for a solar cell according to an embodiment of the present invention, a graphene layer having conductivity between a quantum dot and a semiconductor is shown in FIG. It can be confirmed that the photocurrent and the photocathode excited along the graphene layer formed between the quantum dots are shifted without being recombined when a certain amount of light energy is incident, It can be seen that not only the photocurrent in the quantum dot is increased but also the photoreaction rate is improved.
Therefore, it is preferable that the graphene layer is sandwiched between the plurality of quantum dot layers, as the photoelectrons in the quantum dot layer can efficiently move along the graphene layer as the conductive material as described above.
The number of graphene layers interposed between the plurality of quantum dot layers is more preferably from 3 to 10. The current density / voltage of the photovoltaic cell according to the embodiment of the present invention and the comparative example are measured, Referring to FIG. 6, it can be seen that the characteristics of a battery vary depending on the number and concentration of the graphene layer when applied to a solar cell. That is, the more the graphene layer having conductivity is interposed, the more smooth the movement of the photoelectrons becomes.
As a result, conventionally, the quantum dots having a very small size are mixed with the conductive material or are covalently bonded, making it difficult to perform chemical doping. In the present invention, however, the quantum dots and the conductive material are divided into layers, , Which has a remarkable effect on controlling electrical properties.
Further, in the related art, it is difficult to uniformly distribute the conductive material to the quantum dot thin film, and the aggregation of the quantum dots by the conductive material occurs. However, according to the present invention, since the graphene layer is interposed between the plurality of quantum dot layers, It is possible to control the position, the concentration and the number of layers of the graphene layer, which is a conductive material, so that various types of solar cells can be realized.
The present invention also provides a method for producing a quantum dot layer, which comprises (A) forming a quantum dot layer, (B) forming a graphene layer on the quantum dot layer, and (C) forming a quantum dot layer on the graphene layer And a method for producing the nanocomposite structure.
The step (A) is preferably a step of forming a quantum dot layer, wherein the quantum dot includes at least one selected from the group consisting of CdSe, ZnS, ZnSe, CdTe, CdS, GaN, GaP, InP and GaAs.
More specifically, the quantum dot layer can be implemented by a hot injection method.
The step (B) is a step of forming a graphene layer on the quantum dot layer formed through the step (A), wherein the graphene is first prepared by chemical vapor deposition or chemical exfoliation desirable.
The graphene solution is preferably formed on the upper surface of the quantum dot layer by any one or more methods selected from spin coating, doctor blade, and spray, but is not limited thereto.
The concentration of the graphene is preferably 1 to 50 mg / mL. If the concentration is out of the above range, it is not preferable because short-circuiting of the device or increase of recombination of the photo-generated charge carrier is feared.
In the step (C), it is preferable to form a quantum dot layer by at least one method selected from among spin coating, doctor blade, and spray, and a quantum dot layer is further formed on the upper surface of the graphene layer formed in the step (B) And the graphene layer is interposed between the plurality of quantum dot layers.
The step (B) and the step (C) may be repeatedly performed to form a multi-layered nanocomposite structure, wherein the graphene layer is formed of m layers and the quantum dot layer is formed of n layers desirable. (1? M? 20, 1? N? 20, m, n = integer)
That is, since the formation of the nanocomposite structure through the steps (A) to (C) can not only uniformly distribute the quantum dot to the conductive material but also control the position, concentration and number of layers of the conductive material, Lt; RTI ID = 0.0 > solar cell. ≪ / RTI >
Also, according to the present invention, a solar cell including the nanocomposite structure described above can be provided.
Hereinafter, specific examples will be described in detail.
Production Example 1: Synthesis of Graphene
Graphene was synthesized by chemical exfoliation. In the method using the oxidation-reduction characteristics of graphite, graphite is oxidized with strong acid to form and exfoliate the oxide graphene due to the increased interplanar distance. Then, a 20 mg / mL graphene solution is formed by reducing again with strong acid.
Production Example 2: Synthesis of quantum dot
Quantum dots were synthesized by hot injection method. At high temperatures, additional chalcogenide precursors are injected into the metal precursor solution to induce growth of various nano-sized CdSe quantum dots depending on the reaction conditions.
Example 1
The quantum dot layer of Production Example 2 was formed by spin coating on the ITO substrate on which the ZnO electrode was deposited and the graphene solution of Preparation Example 1 was applied to the surface of the quantum dot layer, Layer, and the graphene layer was formed as a five-layered nanocomposite structure. Then, an Au electrode was deposited to manufacture a solar cell.
Example 2
A nanocomposite having a quantum dot layer of 12 layers and a graphene layer of 9 layers was formed in the same manner as in Example 1 to produce a solar cell.
Comparative Example 1
The quantum dot layer of Production Example 2 was formed into 12 layers by spin coating on a substrate on which an ITO electrode was deposited, and then Au electrodes were deposited to prepare a solar cell.
FIG. 4A is a schematic diagram showing the process of Embodiment 1, wherein a nanocomposite structure is formed such that a quantum dot and a graphene layer are sequentially stacked as described above, and a graphene layer is interposed between quantum dot layers. Through the process, the nanocomposite structure can realize a desired number of layers and shapes according to applications and purposes, and thus can be applied to various applications such as solar cells.
FIG. 4B is a schematic diagram showing a process in which electrons in the graphene layer forming the nanocomposite structure of Example 1 move from LUMO (Lowest Unoccupied Molecular Orbital) to HOMO (Highest Occupied Molecular Orbital) The conductive graphene layer formed on the surface of the photoelectric material plays a role of allowing the photoelectrons to move smoothly before recombination.
5 is a graph showing the results of an analysis of the surface and crystal structure of the quantum dot layer and the graphene layer of Example 1, wherein (a) shows the surface of the quantum dot layer measured by a transmission electron microscope (TEM) This is an image showing the observation result. As can be seen from the above image, it can be confirmed that it has a very excellent crystalline structure with a size of several nanometers (nm).
5 (b) is a graph showing X-ray diffraction (XRD) analysis results for the quantum dot layer. The graph of FIG. 5 (b) is 25.9 ° in the (111) plane, 30.1 ° in the (200) plane, 43 ° in the (311) plane shows a 50.9 占 effective peak.
5 (c) is an image showing the result of observation of the surface of the graphene layer by scanning electron microscopy (SEM), wherein the graphene has an average diameter of 500 nm, It may affect the optical and electrical characteristics of the battery.
FIG. 5 (d) is a graph showing the results of measurement of the graphene layer by Raman spectroscopy. It shows a D band at 1341 cm -1 , a G band at 1574 cm -1 and a 2D band at 2677 cm -1 .
FIG. 6A is a graph showing the results of measurement of current density / voltage for the solar cells of Examples 1 and 2 and Comparative Example 1. As the number of graphene layers is increased, the measured values of current density and voltage are improved .
6B is a graph showing the results of measurement of the solar cell internal resistance values of Examples 1 and 2 and Comparative Example 1. It can be seen that the resistance value of Example 2 is remarkably decreased because the current density and the voltage The results are also consistent with the graph of FIG.
6C is a graph showing measurement results of short circuit current density (Jsc) and energy conversion efficiency (PCE) for the solar cells of Examples 1 and 2 and Comparative Example 1. In FIG. 6C, Energy conversion efficiency is the best.
7 (a) and 7 (b) are graphs showing the results of measurement of the photocurrent and photoreaction rates of the solar cells of Example 2 and Comparative Example 1. FIG. 7 (b) It is a graph.
As shown in the graph, in the case of Example 2, the photocurrent and photoreaction rate, which are relatively increased, can be observed as compared with Comparative Example 1. This phenomenon is due to the fact that, when a certain amount of light energy is incident, the photoelectrons excited along the graphene layer formed between the quantum dots move smoothly without recombination, so that the photocurrent in the quantum dots as a whole increases, .
Therefore, according to the present invention, since the quantum dots of very small size of the prior art are mixed with the conductive material, it is difficult to perform chemical doping and the problem of non-uniformity or aggregation of quantum dots can be solved.
In addition, it is possible to suppress exciton recombination in the quantum dots and induce photoelectric transfer smoothly, thereby making it possible to manufacture a solar cell having high efficiency.
100, 100 '; Quantum dot layer
200; Graphene layer
Claims (12)
Wherein the graphene layer (a) is interposed between a plurality of (b) quantum dot layers to form a structure in which the graphene layer and the quantum dot layer are alternately stacked,
Wherein the graphene layer (a) is formed of m-layer, and the (b) quantum dot layer is formed of n-layer.
(3? M? 10, 1 <n? 20, m, n = integer)
Wherein the total thickness of the quantum dot layer is 50 to 400 nm.
Wherein the quantum dot comprises at least one selected from the group consisting of CdSe, ZnS, ZnSe, CdTe, CdS, GaN, GaP, InP, and GaAs.
Wherein the total thickness of the graphene layer is 0.3 to 7 nm.
(B) forming a graphene layer on the quantum dot layer; And
(C) forming a quantum dot layer on the graphene layer,
The steps (B) and (C) are repeatedly performed,
Wherein the graphene layer is formed of m layers and the quantum dot layer is formed of n layers.
(3? M? 10, 1 <n? 20, m, n = integer)
Wherein the step (B) comprises forming a graphene layer by at least one method selected from spin coating, doctor blade, and spraying.
Wherein the step (C) comprises forming a quantum dot layer by at least one method selected from spin coating, doctor blade, and spray.
Wherein the quantum dot comprises at least one selected from the group consisting of CdSe, ZnS, ZnSe, CdTe, CdS, GaN, GaP, InP, and GaAs.
Wherein the concentration of the graphene is 1 to 50 mg / mL.
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