WO2018208086A1 - Graphene-polycrystalline silicon composite, preparation method therefor, conductor, and substrate - Google Patents

Abstract

In a graphene-polycrystalline silicon composite, a preparation method therefor, a conductor, and a substrate, the graphene-polycrystalline silicon composite is an aggregate of a plurality of unit crystals formed by polycrystalline silicon and has a structure in which graphene is disposed in the crystal grain boundary between the unit crystals.

Description

Graphene-Polycrystalline Silicon Composites, Methods of Manufacturing the Same, Conductors and Substrates

The present invention relates to a graphene-polycrystalline silicon composite, a method for manufacturing the same, a conductor, and a substrate, and more particularly, to a graphene-polycrystalline silicon composite, a method for manufacturing the same, a conductor, and the like, which improve charge transfer characteristics by controlling a polycrystalline silicon interface. It relates to a substrate.

Since silicon (silicon) is abundant in the earth, it is infinite in resources, environmentally friendly because it is non-toxic, and it is easy to control the electrical properties when doping impurities, which is a key material in the semiconductor material industry. It is widely used to.

Meanwhile, due to problems such as environmental pollution and depletion of fossil energy, interest in development of next-generation environmentally friendly energy technology is increasing. Among them, researches on solar cells are being actively conducted, and most of the solar cell industry is made up of silicon solar cells. Development of low-cost, high-efficiency solar cells is required for the development of solar cells, but single crystal silicon solar cells have high efficiency but high price. On the other hand, polycrystalline silicon solar cells have the advantage of low price, but there is a problem that there is a limit to increase the efficiency. Accordingly, there is a continuing demand for improved efficiency of polycrystalline silicon solar cells.

In order to solve the above problems of the prior art, an object of the present invention is to provide a graphene-polycrystalline silicon composite with improved charge transfer characteristics.

Another object of the present invention is to provide a method for producing the graphene-polycrystalline silicon composite.

Still another object of the present invention is to provide a conductor and a substrate including the graphene-polycrystalline silicon composite.

The graphene-polycrystalline silicon composite according to the present invention for the above object is an aggregate of a plurality of unit crystals formed by polycrystalline silicon, and has a structure in which graphene is disposed at grain boundaries between unit crystals.

In one embodiment, a plurality of graphenes may be stacked on the grain boundary.

In an embodiment, an n-type element may be doped into the unit crystals. In this case, as compared with the graphene-free polycrystalline silicon under the same conditions, the electron mobility of the graphene-polycrystalline silicon composite shows a high value. The graphene-free polycrystalline silicon under the same conditions includes polycrystalline silicon doped with n-type elements but no graphene is present at the grain boundaries of the polycrystalline silicon.

In one embodiment, the p-type element may be doped into the unit crystals. In this case, the hole mobility of the graphene-polycrystalline silicon composite exhibits a high value as compared with the graphene-free polycrystalline silicon under the same conditions. The graphene-free polycrystalline silicon under the same conditions includes polycrystalline silicon doped with a p-type element but no graphene is present at the grain boundaries of the polycrystalline silicon.

In one embodiment, the graphene disposed between the unit crystals may be graphene, reduced graphene oxide or graphene oxide.

Graphene-polycrystalline silicon composite production method according to the present invention for another object described above comprises the steps of mixing the silicon powder and graphene oxide powder in a dispersion solvent; Adding a reducing agent to the mixed silicon powder and the graphene oxide powder to prepare a mixed powder in which the reduced graphene oxide is coated on the surface of the silicon powder; And sintering the mixed powder to produce a graphene-polycrystalline silicon composite, wherein the graphene-polycrystalline silicon composite is an aggregate of a plurality of unit crystals formed by polycrystalline silicon, and is located at grain boundaries between the unit crystals. Graphene has a structure arranged.

In an embodiment, the preparing of the graphene-polycrystalline silicon composite may be performed by discharge plasma sintering.

In one embodiment, the silicon powder used in the mixing step may be a silicon powder doped with a p-type element or n-type element.

Each of the conductor and the substrate according to the present invention for another object described above includes the graphene-polycrystalline silicon composite described above.

According to the graphene-polycrystalline silicon composite of the present invention described above, a method of manufacturing the same, a conductor, and a substrate, the graphene-polycrystalline silicon composite having excellent charge transfer characteristics can be obtained by positioning graphene at the grain boundaries of polycrystalline silicon. Since graphene is a material with a unique property that Fermi liquid spontaneously fills up or down the Dirac point under the influence of the Fermi level of the heterogeneous material in contact, In the case of forming an interface between silicon grain boundaries heavily doped with graphene, the effect of grain boundary scattering of charges may be reduced due to band alignment of silicon and graphene, thereby improving charge transfer characteristics of the composite. The interface control effect of the polycrystalline silicon of graphene can be implemented in both n-type and p-type.

1 and 2 are transmission electron microscope (TEM) pictures of the silicon powder and the silicon-reduced graphene oxide composite powder used in the preparation of the composite 1 according to the present invention.

3 to 6 are views for explaining the characteristics of the composite 2 according to the present invention.

7 to 10 are views for explaining the characteristics of the composite 3 according to the present invention.

FIG. 11 is a diagram illustrating a band alignment relationship between n-type and p-type silicon and graphene. FIG.

As the inventive concept allows for various changes and numerous modifications, particular embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific disclosed form, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention. In describing the drawings, similar reference numerals are used for similar elements.

The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In this application, the terms "comprises" or "having" are intended to indicate that there is a feature, step, operation, component, part, or combination thereof described on the specification, and one or more other features or steps. It is to be understood that the present invention does not exclude, in advance, the possibility of the presence or addition of any operation, component, part, or combination thereof.

Unless defined otherwise, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art. Terms such as those defined in the commonly used dictionaries should be construed as having meanings consistent with the meanings in the context of the related art and shall not be construed in ideal or excessively formal meanings unless expressly defined in this application. Do not.

The graphene-polycrystalline silicon composite according to the present invention is a composite having a structure in which graphene is disposed at grain boundaries formed by polycrystalline silicon.

The complex is a collection of a plurality of unit crystals, each of the unit crystals are composed of polycrystalline silicon, the interface between the unit crystals corresponds to a grain boundary and has a structure in which graphene is disposed at this grain boundary.

In this case, the graphene disposed at the grain boundary may be graphene, graphene oxide, or reduced graphene oxide. For example, graphene-polycrystalline silicon composite may be prepared by reducing graphene oxide using graphene oxide.

Graphene has a unique property that the Fermi liquid spontaneously fills up or down the Dirac point due to the Fermi level of the polycrystalline silicon, which is in contact with the heterogeneous material. As a result, when the graphene is disposed in the polycrystalline silicon grain boundary, the effect of grain boundary scattering of the charge may be reduced due to the band alignment of the polycrystalline silicon and the graphene, thereby improving charge transfer characteristics of the composite. That is, not only charges are conducted through the percolate graphene network but also through the band alignment of polycrystalline silicon and graphene, the effect of grain boundary scattering of charges is reduced, thereby improving charge transfer characteristics of polycrystalline silicon. Has the characteristic of being. The interface control effect of the polycrystalline silicon of graphene can be implemented in both n-type and p-type.

Silicon is a material in which electrons and holes exist in the same number due to thermal equilibrium even when undoped, and electrical conduction by electrons and holes is possible at the same time. As possible substance. In addition, silicon is fundamentally different from other oxide semiconductors in which an electronic band structure, which is an elemental semiconductor, mainly determines n-type electronic band structure. Therefore, the mechanism in which the electrical conductivity is improved by graphene disposed at grain boundaries of unit crystals is fundamentally different from that of other oxide semiconductors.

In one embodiment, the unit crystals may be polycrystalline silicon doped with an n-type element. At this time, the electron mobility of the graphene-polycrystalline silicon composite according to the present invention exhibits a high value as compared with pure polycrystalline silicon under the same conditions. Arsenic (As) is mentioned as an n-type element. In polycrystalline silicon doped with n-type elements in unit crystals, the mobility of electrons, that is, electron mobility, in the conduction band of silicon is improved by graphene disposed at grain boundaries of the unit crystals.

In another embodiment, the unit crystals may be polycrystalline silicon doped with a p-type element. At this time, the hole mobility of the graphene-polycrystalline silicon composite according to the present invention exhibits a high value as compared with pure polycrystalline silicon under the same conditions. Aluminum, boron, gallium, indium etc. are mentioned as a p-type element. Although there is no known change in the hole mobility due to graphene disposed at the grain boundary or its correlation, the inventors of the present invention have unit crystals composed of polycrystalline silicon doped with p-type elements, and between these unit crystals. It was confirmed that the hole mobility of the graphene-polycrystalline silicon composite is increased due to the arrangement of graphene at the grain boundary of the composite, and thus the composite having the higher hole mobility may be invented.

In particular, in the present invention in which polycrystalline silicon doped with a p-type element forms a unit crystal and graphene is disposed at grain boundaries between the unit crystals, a valence that is a charge carrier having a property opposite to that of electrons hole mobility of the band), that is, hole mobility is improved. Because holes are charge transporters having opposite properties to electrons, there is no particular correlation between electron mobility and hole mobility, but the inventors of the present invention have found that the grain boundary between the unit crystals of graphene is composed of polycrystalline silicon doped with p-type element. It has been found that the hole mobility of the graphene-polycrystalline silicon composite can be improved by placing it in the.

That is, in the present invention, since the unit crystal is made of silicon, both n-type and p-type can be realized, and thus the composite including the unit crystal made of polycrystalline silicon doped with n-type elements has a high hole mobility. The composite including unit crystals made of polycrystalline silicon doped with a p-type element is implemented to have high electron mobility.

The graphene-polycrystalline silicon composite according to the present invention may be prepared by first mixing a silicon powder and a graphene oxide powder, adding a reducing agent to synthesize a silicon-reduced graphene oxide composite powder, and then sintering it. The silicon powder may be a silicon powder doped with a p-type or n-type element. In the case where the impurity doped silicon powder is used, the polycrystalline silicon included in the graphene-polycrystalline silicon composite may be finally doped with impurities.

In the sintering process, the silicon-reduced graphene oxide composite powder may be sintered by a discharge plasma sintering method to prepare a graphene-polycrystalline silicon composite.

Since the sintering process proceeds under a high temperature and vacuum atmosphere, not only to prepare a sintered body, but also to thermally reduce the chemically reduced graphene oxide secondarily using a reducing agent. The chemically / thermally reduced graphene oxide prepared as described above has electrical properties similar to graphene.

Hereinafter, the composite according to the present invention and a method for preparing the same will be described in more detail through evaluation of properties of specific preparation examples and the prepared composite.

Preparation Example 1 Preparation of Complex 1

The powder was prepared by dispersing the silicon powder and graphene oxide pulverized to about 300 nm size in 200 ml of dimethylformamide using a specmill and then stirred for 5 minutes to prepare a mixed powder. The silicon-reduced graphene oxide composite powder was prepared by adding hydrazine monohydrate to the mixed powder and reacting at 80 ° C. for 1 hour in a heating mantle to chemically reduce graphene oxide. The content of graphene oxide at this time was adjusted to 1% by weight. After completion of the reaction, the solution was aged at room temperature for 24 hours to stabilize the structure, followed by centrifugation at 10,000 rpm for 10 minutes, and then dried in a vacuum oven at 40 ° C for 24 hours to finally reduce the graphene oxide-silicon oxide composite powder. Got it. The obtained reduced graphene oxide-silicon composite powder was sintered by the discharge plasma sintering method. The temperature of the sintering process was 1,300 degreeC, the sintering time was 30 minutes, and the sintering pressure was 100 MPa. The graphene oxide-polycrystalline silicon composite finally cooled by sintering was synthesized.

Check the structure of silicon powder and composite powder: TEM photo

Transmission electron micrographs were taken for each of the silicon powder used for the preparation of the composite 1 and the silicon-reduced graphene oxide composite powder, which is an intermediate product before the formation of the composite 1. The results are shown in FIGS. 1 and 2.

1 and 2 are transmission electron microscope (TEM) images of the silicon powder and the silicon-reduced graphene oxide composite powder used in the preparation of the composite 1 according to the present invention.

1 and 2, it can be seen that the silicon powder used as a raw material has a size of about 300 nm, the silicon powder in the silicon-reduced graphene oxide composite powder by reducing the graphene oxide using a reducing agent It can be seen that the reduced graphene oxide is coated on the surface. At this time, it can be confirmed through the TEM photograph that the reduced graphene oxide coated on the surface of the silicon powder is laminated in a plurality of layers.

Preparation Example 2 Preparation of Complex 2

Except that arsenic was doped as n-type doping element in Composite 1 by using arsenic doped silicon powder. Substantially the same process as preparing the composite 1 was carried out to prepare a composite 2 which is a arsenic doped reduced graphene oxide-polycrystalline silicon composite.

Characterization of Complex 2

For Composite 2 prepared as above, the relationship between the carrier concentration at room temperature and the charge mobility (i.e., electron mobility), the change in charge mobility with temperature, the change in carrier concentration with temperature, and the electricity with temperature Each change in conductivity was measured. The results are shown in FIGS. 3 to 6.

3 to 6 are views for explaining the characteristics of the composite 2 according to the present invention. In each of FIGS. 3 to 6, the results of the composite 2 (Δ) and the comparative examples thereof are similar to those of the arsenic-doped n-type silicon wafer (□) and the arsenic-doped n-type polycrystalline silicon sintered body (○). Indicates.

3 is a graph showing the relationship between the carrier concentration (unit: cm ^-3 ) and the charge mobility (unit: cm ² V ^-1 s ^-1 ) at room temperature, the carrier in the arsenic doped n-type single crystal silicon The values calculated using Masetti's formula showing charge mobility with concentration are shown as solid lines.

Referring to FIG. 3, for the same carrier concentration condition, the n-type polycrystalline silicon sintered body (○) has a charge mobility (about 100 cm ² V ⁻¹ s ^{− 1} ) of the single crystal silicon calculated by the Masseti formula due to grain boundary scattering. It appears to have a significantly lower charge mobility compared to (about 25 cm ² V ^-1 s ^-1 level). On the other hand, it can be seen that the charge mobility of the composite 2 (Δ) whose interface is controlled by the reduced graphene oxide shows about twice the charge mobility of the n-type polycrystalline silicon sintered body (○).

4 is a graph showing the change in charge mobility with temperature (unit: K).

Referring to FIG. 4, the charge mobility in the material is largely determined by the influence of grain boundary scattering, ionized impurity scattering, and phonon scattering according to the Masshiessen's rule. The charge is scattered. As a result, it can be seen that, as in the aspect of the n-type polycrystalline silicon sintered body (○), the charge mobility tends to increase with temperature.

However, in the composite 2 (△) according to the present invention, due to the band alignment of silicon and graphene, the effect of grain boundary scattering of the charge is reduced, thereby increasing charge mobility and decreasing grain boundary scattering effect, thereby reducing the n-type silicon wafer ( Similar to □), it can be seen that the charge mobility of the complex 2 (△) shows an inverse relationship with the temperature.

5 is a graph showing the change in charge mobility with temperature. In FIG. 5, the carrier concentrations of the composite 2 (Δ), the n-type silicon wafer (□), and the n-type polycrystalline silicon sintered body (○) do not tend to be significantly different. It can be seen that indicates.

6 is a graph showing the change in electrical conductivity (unit Scm ^-1 ) with temperature, and the electrical conductivity of the composite 2 (△) according to the present invention compared to the n-type polycrystalline silicon sintered body (○) through FIG. It can be seen that the overall value shows a high value according to the change in temperature.

Preparation Example 3 Preparation of Complex 3

Reduced graphene oxide doped with boron by carrying out substantially the same process as the preparation of the composite 1, except that boron was doped into the composite 1 by using a boron-doped silicon powder. Composite 3, a polycrystalline silicon composite, was prepared.

Characterization of Complex 3

For the composite 3 prepared as above, the relationship between the carrier concentration and the charge mobility (ie, hole mobility) at room temperature, the change in the charge mobility with temperature, the change in the carrier concentration with temperature, and the electricity with temperature Each change in conductivity was measured. The results are shown in FIGS. 7 to 10.

7 to 10 are views for explaining the characteristics of the composite 3 according to the present invention. In Figures 7 to 10, the results for the composite 3 (◇) and, as a comparative example, the results for the boron-doped p-type silicon wafer (▽) is shown together.

Referring to Figures 7 to 10, the temperature dependence of the charge mobility of the composite 3 (◇) tends to decrease the mobility as the temperature increases, which is the effect of grain boundary scattering through the interface control using graphene It can be seen that this is reduced, and from this result, it can be seen that the improvement of charge transfer characteristics through interface control using graphene is applicable to not only n-type silicon but also p-type silicon. In addition, also in the other properties it can be seen that the properties of the composite 3 (◇) appear similar to the properties of the composite 2 (△) shown in Figures 3 to 6.

FIG. 11 is a diagram illustrating a band alignment relationship between n-type and p-type silicon and graphene. FIG.

Referring to FIGS. 3 to 10 together with FIG. 11, graphene is a material without a bandgap, and a Fermi liquid whose electron or hole concentration changes depending on the Fermi level of the material in contact with the graphene. It is a substance with properties. Therefore, when graphene is located at the interface between the heavily doped silicon grain boundaries, charges passing through the interface between silicon and graphene may be free from grain boundary scattering due to the band alignment of silicon and graphene. As a result, the effect of grain boundary scattering of charges is reduced, thereby improving charge transfer characteristics of the composite.

In the above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications may be made by those skilled in the art within the scope of the technical idea of the present invention. Modifications are possible.

Claims (12)

1. Is a collection of a number of unit crystals formed by polycrystalline silicon,

   Characterized in that the graphene is arranged in the grain boundary between the unit crystals,

   Graphene-polycrystalline silicon composite.
2. The method of claim 1,

   Characterized in that a plurality of graphene is stacked and disposed in the grain boundary,

   Graphene-polycrystalline silicon composite.
3. The method of claim 1,

   Graphene-polycrystalline silicon composite, characterized in that the n-type element is doped in the unit crystals.
4. The method of claim 3,

   Compared to the graphene-free polycrystalline silicon of the same conditions, characterized in that the electron mobility (electron mobility) shows a high value,

   Graphene-polycrystalline silicon composite.
5. The method of claim 1,

   Graphene-polycrystalline silicon composite, characterized in that the unit crystals doped with a p-type element.
6. The method of claim 5,

   In comparison with the graphene-free polycrystalline silicon of the same conditions, it characterized in that the hole mobility (hole hole) shows a high value,

   Graphene-polycrystalline silicon composite.
7. The method of claim 1,

   Graphene disposed between the unit crystals

   It is characterized in that the graphene, reduced graphene oxide or graphene oxide,

   Graphene-polycrystalline silicon composite.
8. Mixing the silicon powder and the graphene oxide powder in a dispersion solvent;

   Adding a reducing agent to the mixed silicon powder and the graphene oxide powder to prepare a mixed powder in which the reduced graphene oxide is coated on the surface of the silicon powder; And

   Sintering the mixed powder to prepare a graphene-polycrystalline silicon composite,

   The graphene-polycrystalline silicon composite is a collection of a plurality of unit crystals formed by polycrystalline silicon, characterized in that having a structure in which graphene is disposed at grain boundaries between the unit crystals,

   Method for preparing graphene-polycrystalline silicon composite.
9. The method of claim 8,

   The step of preparing the graphene-polycrystalline silicon composite, characterized in that performed by the discharge plasma sintering method,

   Method for preparing graphene-polycrystalline silicon composite.
10. The method of claim 8,

    The silicon powder used in the mixing step is characterized in that the silicon powder doped with p-type element or n-type element,

    Method for preparing graphene-polycrystalline silicon composite.
11. A conductor comprising the graphene-polycrystalline silicon composite according to any one of claims 1 to 7.
12. A substrate formed of the graphene-polycrystalline silicon composite according to any one of claims 1 to 7.

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