KR20120029332A - Graphene quantum dot light emitting device and method of manufacturing the same - Google Patents

Abstract

PURPOSE: A graphene quantum dot light emitting and a manufacturing method thereof are provided to form a band gap of a graphene quantum dot layer small by controlling size and shape of a graphene quantum dot. CONSTITUTION: First graphene(20) is n-type graphene. Second graphene(40) is p-type graphene. A graphene quantum dot layer(30) is located on the first graphene. The graphene quantum dot layer comprises a plurality of graphene quantum dots. The graphene quantum dot layer contain organic solvents. The second grapheme is located on the graphene quantum dot layer. An electron transport layer is located between the n-type grapheme and the graphene quantum dot layer. A hole transport layer is located between the graphene quantum dot layer and the p-type graphene.

Description

Graphene quantum dot light emitting device and method of manufacturing the same

It relates to a graphene quantum dot light emitting device and a method of manufacturing the same.

A quantum dot electroluminescence device (QD-EL) is a three-layered device including a hole transport layer (HTL) and an electron transport layer (ETL) at both ends with a quantum dot emission layer interposed therebetween. Known as the base element.

A quantum dot is a semiconductor material with a crystal structure of several nanoscales and is composed of hundreds to thousands of atoms. Because quantum dots are very small, they have a large surface area per unit volume, most atoms are present on the surface of nanocrystals, and exhibit quantum confinement effects. By the quantum confinement effect, the emission wavelength can be adjusted only by controlling the size of the quantum dot, and has been attracting attention due to its excellent color purity and high PL (photoluminescence) emission efficiency.

However, there is a problem in that the efficiency of the quantum dot light emitting device is low due to the compatibility with the organic material used as the major and electron transport layer, the absence of highly efficient semiconductor nanoparticles, and the like. Therefore, researches to improve the efficiency of the quantum dot light emitting device have been actively conducted in recent years.

Provided are a graphene quantum dot light emitting device and a method of manufacturing the same.

Graphene quantum dot light emitting device according to an embodiment of the present invention

First graphene;

A graphene quantum dot layer provided on the first graphene and having a plurality of graphene quantum dots; And

The second graphene provided on the graphene quantum dot layer; may be.

The first graphene may be n-type graphene, and the second graphene may be p-type graphene.

It may further include an electron transport layer provided between the n-type graphene and the graphene quantum dot layer.

The electron transport layer may include TPBi, PBD, BCP, BAlq or OXD7.

It may further include a hole transport layer provided between the graphene quantum dot layer and the p-type graphene.

The hole transport layer may include poly-TPD, PEDOT, PSS, PPV, PVK, TFB, PFB, TBADN, NPB, Spiro-NPB, DMFL-NPB, DPFL-NPB, or mHOST5.

The graphene quantum dot layer may further include an organic solvent.

The size of the plurality of graphene quantum dots may be 1 to 30 nm.

The n-type graphene may be graphene doped with one selected from nitrogen (N), fluorine (F), and manganese (Mn).

The p-type graphene may be graphene doped with one selected from oxygen (O), gold (Au), and bismuth (Bi).

The first graphene may further include a first contact pad provided on the first graphene and spaced apart from the graphene quantum dot layer and the second graphene, or provided on a bottom surface of the first graphene.

The display device may further include a second contact pad provided on the second graphene.

Graphene quantum dot light emitting device manufacturing method according to another embodiment of the present invention

Forming a first graphene doped with a first dopant;

Forming a graphene quantum dot layer having a plurality of graphene quantum dots on the first graphene; And

It may include; forming a second graphene doped with a second dopant on the graphene quantum dot layer.

The first dopant may be an n-type dopant, and the second dopant may be a p-type dopant.

The n-type dopant may be one selected from nitrogen (N), fluorine (F), and manganese (Mn).

The p-type dopant may be one selected from oxygen (O), gold (Au), and bismuth (Bi).

The method may further include forming an electron transport layer between the first graphene and the graphene quantum dot emission layer.

The electron transport layer may include TPBi, PBD, BCP, BAlq or OXD7.

The method may further include forming a hole transport layer between the graphene quantum dot emission layer and the second graphene.

The hole transport layer may include poly-TPD, PEDOT, PSS, PPV, PVK, TFB, PFB, TBADN, NPB, Spiro-NPB, DMFL-NPB, DPFL-NPB, or mHOST5.

The plurality of graphene quantum dots may be formed by pulverizing the graphite by applying ultrasonic waves to a solution containing graphite.

The plurality of graphene quantum dots may be formed by heating graphite oxide to reduce a portion thereof and cutting the reduced portion of the graphite oxide.

The graphene quantum dot layer may be formed by spin coating the plurality of graphene quantum dots on the first graphene.

The present invention is a graphene quantum dot light emitting device, the luminous efficiency can be improved than the conventional quantum dot light emitting device. In addition, it is possible to implement a light emitting device with graphene to be flexible, and to implement a light emitting device having various designs. In addition, since the graphene quantum dots are more durable than the conventional semiconductor-based quantum dots, the lifespan of the graphene quantum dot light emitting device of the present invention may be increased.

In addition, the manufacturing method of the graphene quantum dot light emitting device of the present invention, in place of the compound semiconductor requiring an expensive metal-organic chemical vapor deposition (MOCVD) equipment, chemical vapor deposition (Chemical Vapor Deposition): It is possible to manufacture by CVD equipment, it is possible to lower the manufacturing cost and shorten the process time compared to the conventional compound semiconductor light emitting device.

1 is a schematic cross-sectional view of a graphene quantum dot light emitting device according to an embodiment of the present invention.
2 illustrates a plurality of graphene quantum dots provided on the first graphene.
FIG. 3 illustrates a plurality of graphene quantum dots regularly provided on the first graphene.
4 illustrates a plurality of graphene quantum dots regularly provided on the first graphene.
5A to 5C are plan views illustrating shapes of graphene quantum dots.
6 is a schematic cross-sectional view of a graphene quantum dot light emitting device according to another embodiment of the present invention.
FIG. 7 is a schematic example of an energy band structure of the graphene quantum dot light emitting device illustrated in FIG. 6.
8A to 8D schematically illustrate light emission characteristics of the graphene quantum dot light emitting device illustrated in FIG. 6.
9A to 9F schematically illustrate steps of a method of manufacturing a graphene quantum dot light emitting device according to an embodiment of the present invention.
10A to 10D schematically illustrate steps of a method of manufacturing a graphene quantum dot light emitting device according to another embodiment of the present invention.
11A to 11D schematically illustrate light emission characteristics of a graphene quantum dot light emitting device according to various experimental examples.
12A to 12D schematically illustrate light emission characteristics of the graphene quantum dot light emitting device according to various experimental examples.

Hereinafter, with reference to the accompanying drawings, it will be described in detail the disclosed graphene quantum dot light emitting device and its manufacturing method. In the following drawings, the same reference numerals refer to the same components, the size of each component in the drawings may be exaggerated for clarity and convenience of description.

1 is a schematic cross-sectional view of a graphene quantum dot light emitting device 100 according to an embodiment of the present invention.

Referring to FIG. 1, the graphene quantum dot light emitting device 100 according to the present embodiment is provided on a substrate 10, a first graphene 20 provided on the substrate 10, and a first graphene 20. The graphene quantum dot layer 30 may include a second graphene 40 provided on the graphene quantum dot layer 30. In addition, the graphene quantum dot light emitting device 100 of the present exemplary embodiment may include a first contact pad provided spaced apart from the graphene quantum dot layer 30 and the second graphene 40 in an exposed area on the first graphene 20. 50) may be further included. In addition, the graphene quantum dot light emitting device 100 of the present embodiment may further include a second contact pad 55 provided on the second graphene 40.

The substrate 10 may be made of, for example, a material such as glass, sapphire, polyethylene terephthalate (PET), Si, ZnO, GaAs, SiC, MgAl 2 O 4, MgO, LiAlO 2, LiGaO 2, GaN, or the like. The substrate 10 may be removed after forming the first graphene 20, the graphene quantum dot layer 30, and the second graphene 30 thereon. Meanwhile, in the graphene quantum dot light emitting device 100 according to the present embodiment, the first graphene 20 may serve as a substrate without a separate substrate 10.

The first graphene 20 may be provided on the substrate 20. Graphene is a conductive material with carbon atoms in a honeycomb arrangement in two dimensions, one layer thick. Graphene is structurally and chemically very stable and is a good conductor, having faster charge mobility than silicon, and allowing more current to flow than copper. In addition, graphene has excellent transparency, and may have a higher transparency than indium tin oxide (ITO), which is conventionally used as a transparent electrode. The undoped graphene does not have an energy band gap where the conduction band and the valence band meet each other, but an energy band gap occurs as the n-type dopant or the p-type dopant is doped into the graphene. The energy band gap may be adjusted according to the type, doping concentration, etc. of the n-type or p-type dopant.

Here, the first graphene 20 may be n-type graphene 20. That is, the first graphene 20 may be used as the n-type electrode to the electron transport layer. The n-type graphene 20 is doped with at least one graphene sheet (graphene sheet) with the n-type dopant. The graphene sheet may be formed on the substrate 10 by chemical vapor deposition (CVD), mechanical or chemical exfoliation, epitaxial growth, or the like. Meanwhile, the graphene sheet may be formed on an auxiliary substrate made of PDMS, and then transferred onto the substrate 10. Then, the n-type dopant is injected and adsorbed onto the graphene sheet, the n-type graphene 20 may be formed. The n-type dopant may be, for example, nitrogen (N), fluorine (F), or manganese (Mn), but is not limited thereto. On the other hand, the thickness of the first graphene 20 may be about 0.34nm, when the first graphene 20 has a structure in which a plurality of graphene sheets are stacked, the thickness of the first graphene 20 is about It may be an integer multiple of 0.34 nm. Since the thickness of the first graphene 20 is thinner than the wavelength of light generated in the graphene quantum dot layer 30, total reflection may not occur at the interface between the two layers.

Since the first graphene 20 has excellent electrical conductivity, a separate first electrode may not be provided. However, a first contact pad 50 may be provided spaced apart from the graphene quantum dot layer 30 and the second graphene 40 on the first graphene 20. That is, the first contact pad 50 has a mesa structure in which the graphene quantum dot layer 30 and the second graphene 40 are mesa etched to expose a portion of the first graphene 20. It may be provided on the exposed part of the first graphene 20. Meanwhile, as shown in FIG. 9E, when the first contact pad 50 uses a conductive substrate as the substrate 10, the first graphene 20 of the substrate 10, that is, the lower surface of the substrate 10, is used. It may be formed on the side facing the formed surface. Alternatively, as shown in FIG. 9F, the first contact pad 50 removes the substrate 10, and the lower surface of the first graphene 20, that is, The graphene quantum dot layer 30 of the first graphene 20 may be formed on a surface facing the surface. In addition, the first contact pad 50 may inject electrons into the first graphene 20.

The graphene quantum dot layer 30 may be provided on the first graphene 20, and may emit light having a predetermined energy by recombination of electrons and holes. The graphene quantum dot layer 30 may include a plurality of graphene quantum dots, and the plurality of graphene quantum dots may be arranged in various forms on the first graphene 20. Detailed description thereof will be described with reference to FIGS. 2 to 4.

The graphene quantum dot may be about 1 nm to 30 nm, or about 1 nm to 20 nm, more specifically 1 nm to 10 nm size graphene nano-flakes. In addition, graphene quantum dots may be further bonded to the functional group on the surface (edge). An amine-based functional group may be attached to the graphene quantum dot, for example, an alkylamine, aniline, or PEG may be attached. The graphene quantum dots have a large number of electrons therein, but the number of free electrons may be limited to about 1 to 100. In this case, the energy levels of the electrons may be discontinuously limited, and thus may exhibit electrical and optical characteristics different from those of the graphene in the form of sheets forming continuous bands. Since the graphene quantum dots have different energy levels depending on their size and shape, the band gap may be adjusted by changing their size and shape. That is, the emission wavelength may be adjusted only by adjusting the size and shape of the graphene quantum dots. In addition, since the state density of electrons and holes in the bandgap edge of the graphene quantum dot is much higher than that of the graphene sheet, the number of excited electrons and holes may be combined to improve luminous efficiency.

The second graphene 40 may be provided on the graphene quantum dot layer 30. Here, the second graphene 40 may be p-type graphene 40. That is, the second graphene 40 may be a hole transport layer. The p-type graphene 40 is doped with at least one graphene sheet with a p-type dopant. The graphene sheet may be formed by chemical vapor deposition (CVD), mechanical or chemical exfoliation, epitaxial growth, or the like. The p-type graphene 40 may be formed by injecting and adsorbing the p-type dopant to the graphene sheet. The p-type dopant may be, for example, oxygen (O), gold (Au), bismuth (Bi), or the like, but is not limited thereto. Meanwhile, the thickness of the second graphene 40 may be about 0.34 nm, and in the case where the structure of the plurality of graphene sheets is stacked, the thickness of the second graphene 40 may be an integer multiple of about 0.34 nm. Since the thickness of the second graphene 40 is thinner than the wavelength of the light generated in the graphene quantum dot layer 30, total reflection may not occur at the interface between the two layers.

Since the second graphene 40 has excellent electrical conductivity, a separate second electrode may not be provided. However, a second contact pad 55 may be provided on the second graphene 40. The second contact pad 55 may inject holes into the second graphene 40. In the above description, the first and second graphenes 20 and 40 may be n-type and p-type graphene, respectively, but the first and second graphenes 20 and 40 may be p-type and n-type graphene, respectively. have. The graphene quantum dot light emitting device 100 according to the present exemplary embodiment may improve light emission efficiency than the conventional quantum dot light emitting device, and may implement flexible light emitting devices using graphene and implement light emitting devices having various designs. In addition, since the graphene quantum dot is more durable than the conventional semiconductor-based quantum dot, the lifespan of the graphene quantum dot light emitting device 100 according to the present embodiment may be long.

2 illustrates a plurality of graphene quantum dots 35 provided on the first graphene 20. Referring to FIG. 2, a plurality of graphene quantum dots 35 are randomly provided on the first graphene 20. In FIG. 2, the distance between the graphene quantum dots 35 is exaggerated, and the distance between the graphene quantum dots 35 may be several nm or less.

3 illustrates a plurality of graphene quantum dots 35 regularly provided on the first graphene 20. Referring to FIG. 3, a plurality of graphene quantum dots 35 are arranged at regular intervals on the first graphene 20. That is, the plurality of graphene quantum dots 35 are regularly spaced apart from each other by a predetermined interval on the first graphene 20.

4 illustrates a plurality of graphene quantum dots 35 regularly provided on the first graphene 20. Referring to FIG. 4, the plurality of graphene quantum dots 35 are arranged on the first graphene 20 without being spaced apart from each other and in contact with each other. That is, the plurality of graphene quantum dots 35 are arranged on the first graphene 20 in a row and a column. 2 to 4 illustrate a form in which a plurality of graphene quantum dots 35 are arranged on the first graphene 20, for example, but the arrangement of the graphene quantum dots 35 is not limited thereto. It can be arranged in an array form. For example, the graphene quantum dot layer 30 may have a structure in which a plurality of graphene quantum dots 35 are stacked.

5A to 5C are plan views illustrating shapes of the graphene quantum dots 35, 36, and 37.

Referring to FIG. 5A, the graphene quantum dot 35 may have a shape close to a circle, for example. As illustrated in FIG. 5B, the graphene quantum dot 36 may have a shape in which an ellipse or a rectangle and a circle are combined. In addition, the graphene quantum dot 37 may have a hexagonal shape, as shown in FIG. 5C. However, the shape of the graphene quantum dots (35, 36, 37) is not limited to this, and may be a polygonal shape, such as a square, a pentagon. In addition, graphene quantum dots 35, 36, and 37 may be difficult to define their shape as nano-pieces of graphene.

6 is a schematic cross-sectional view of a graphene quantum dot light emitting device 200 according to another embodiment of the present invention.

Referring to FIG. 6, the graphene quantum dot light emitting device 200 according to the present embodiment is provided on the substrate 210, the first graphene 220 and the first graphene 220 provided on the substrate 210. The graphene quantum dot layer 230 may include a second graphene 240 provided on the graphene quantum dot layer 230. In addition, the graphene quantum dot light emitting device 200 includes a first charge transport layer 225 provided between the first graphene 220 and the graphene quantum dot layer 230, and the graphene quantum dot layer 230 and the second graphene. It may further include a second charge transport layer 235 provided between the 240. In addition, the graphene quantum dot light emitting device 200 may include a first contact pad 250 spaced apart from the graphene quantum dot layer 230 and the second graphene 240 on an exposed area of the first graphene 220. And a second contact pad 255 provided on the second graphene 240.

The substrate 210 may be made of a polymer material such as, for example, glass, sapphire or polyethylene terephthalate (PET). In addition, the substrate 210 may be made of a material such as Si, ZnO, GaAs, SiC, MgAl 2 O 4, MgO, LiAlO 2, LiGaO 2, or GaN. The substrate 210 has a first graphene 220, a first charge transport layer 225, a graphene quantum dot layer 230, a second charge transport layer 235 and a second graphene 240 formed thereon It may be removed. Meanwhile, in the graphene quantum dot light emitting device 200 according to the present embodiment, the first graphene 220 may serve as a substrate without a separate substrate 210.

The first graphene 220 may be provided on the substrate 210. Graphene is a conductive material with carbon atoms in a honeycomb arrangement in two dimensions, one layer thick. Graphene is structurally and chemically very stable and is a good conductor, having faster charge mobility than silicon, and allowing more current to flow than copper. In addition, graphene has excellent transparency, and may have a higher transparency than indium tin oxide (ITO), which is conventionally used as a transparent electrode. The undoped graphene does not have an energy band gap where the conduction band and the valence band meet each other, but an energy band gap occurs as the n-type dopant or the p-type dopant is doped into the graphene. The energy band gap can be controlled according to the type, doping concentration, etc. of the n-type or p-type dopant.

Here, the first graphene 220 may be n-type graphene 220. The first graphene 220 may be used as an n-type electrode of the quantum dot light emitting device 200. The n-type graphene 220 is doped with at least one graphene sheet with an n-type dopant. That is, n-type dopants may be injected and adsorbed onto the graphene sheet to form n-type graphene 220. The n-type dopant may be, for example, nitrogen (N), fluorine (F), or manganese (Mn), but is not limited thereto. Meanwhile, the thickness of the first graphene 220 may be about 0.34 nm, and when the first graphene 220 is formed by stacking a plurality of graphene sheets, the first graphene 220 may be an integer multiple of about 0.34 nm. Since the thickness of the first graphene 220 is smaller than the wavelength of light generated in the graphene quantum dot layer 230, total reflection may not occur at an interface between the two layers.

The first contact pad 250 may include a first charge transport layer 225, a graphene quantum dot layer 230, a second charge transport layer 235, and a second graphene on the first graphene 220. 240 may be provided spaced apart. That is, the first contact pad 250 may be formed by mesa etching the first charge transport layer 225, the graphene quantum dot layer 230, the second charge transport layer 235, and the second graphene 240. In a mesa structure in which a part of the first graphene 220 is exposed, the first graphene 220 may be provided on the exposed part of the first graphene 220. On the other hand, as shown in FIG. 10C, when a conductive substrate is used as the substrate 210, the first contact pad 250 may have a lower surface of the substrate 210, that is, the first graphene 220 of the substrate 210. It may be formed on the side facing the formed surface. Alternatively, as shown in FIG. 10D, the first contact pad 250 removes the substrate 210, and the lower surface of the first graphene 220, that is, the graphene quantum dot layer of the first graphene 220 is removed. It may be formed on the surface facing the surface 230 is formed. The first contact pad 250 may inject electrons into the first graphene 220 from an external power source.

The first charge transport layer 225 may be provided on the first graphene 220. When the first graphene 220 is n-type graphene, the first charge transport layer 225 may be an electron transport layer (ETL). The first charge transport layer 225 is, for example, TPBi (1,3,5-tris (N-phenylbenzimidazol-2, yl) benzene), PBD (2- (4-Biphenylyl) -5- (4-tert- butylphenyl) -1,3,4-oxadiazole), BCP (2,9-Dimethyl-4,7-diphenyl-1,10-phenanhro-line), BAlq (Bis- (2-methyl-8-quinolinolate) -4 -(phenylphe nolato) aluminium) or OXD7 (1,3-bis (N, Nt-butyl-phenyl) -1,3,4-oxadiazole). For example, the first charge transport layer 225 may be formed by spin coating or depositing TPBi on the first graphene 220. In addition, the first charge transport layer 225 made of TPBi may be UV treated to become hydrophilic. As described above, when the first charge transport layer 225 is made of a polymer material, it is possible to structurally prevent deterioration of the quantum dot light emitting device 200 due to oxidation or corrosion, and to lower the turn-on voltage. Meanwhile, an electron injection layer (EIL, not shown) may be further provided between the first graphene 220 and the first charge transport layer 225.

The graphene quantum dot layer 230 may be provided on the first charge transport layer 225 and may emit light having a predetermined energy by recombination of electrons and holes. The graphene quantum dot layer 230 may include a plurality of graphene quantum dots, and the plurality of graphene quantum dots may be arranged in various forms on the first charge transport layer 225. For a detailed description thereof, refer to the description of FIGS. 2 to 4. The graphene quantum dot layer 230 may be formed by spin coating a solution including a plurality of graphene quantum dots on the first charge transport layer 225 and drying the solution through heat treatment. In addition, the solution may further include an organic solvent, for example, polyethylene oxide (PEO), PES and the like.

The graphene quantum dots may be graphene nanoflakes having a size of about 1 nm to about 30 nm, or about 1 nm to about 20 nm, more specifically about 1 nm to about 10 nm. In addition, graphene quantum dots may be further bonded to the functional group on the surface (edge). An amine-based functional group may be attached to the graphene quantum dot, for example, an alkylamine, aniline, or PEG may be attached. The characteristics of the graphene quantum dot may be as described above.

The second charge transport layer 235 may be provided on the graphene quantum dot layer 230. The second charge transport layer 235 may be a hole transport layer (HTL) when the second graphene 240 is p-type graphene. The second charge transport layer 235 is, for example, poly-TPD (N, N'-bis (3-methylphenyl) -N, N'-bis (phenyl) -benzidine), PEDOT (poly (3,4-ethylenedioxythiophene) )), PS (poly (styrenesulfonate)), PPV (poly (p-phenylene vinylene)), PVK (poly (N-vinylcarbazole)), TFB (poly [(9,9-dioctylfluorenyl-2, 7-diyl)- co- (4,4 '(N- (4-sec-butylphenyl))) diphenylamine]), PFB, TBADN (3-Tert-butyl-9,10-di (naphth-2-yl) anthracene), NPB ( N, N`-bis (1-naphtalenyl) -NN`-bis (phenyl-benzidine)), Spiro-NPB (N, N'-di (naphthalen-1-yl) -N, N'-diphenyl-spiro) , DMFL-NPB (N, N'-di (naphthalene-1-yl) -N, N'-diphenyl-9,9'-dimethyl-fluorene), DPFL-NPB (N, N'-di (naphthalen-1) -yl) -N, N'-diphenyl-9,9'-diphenyl-fluorene), mHOST5 (2,7-Di (N, N'-carbarzolyl) -9,9-bis [4- (2-ethylhexyloxy) -phenyl] fluorine). The second charge transport layer 235 may be formed by a wet coating method such as spin coating. For example, the second charge transport layer 235 may be formed by spin coating or depositing poly-TPD on the graphene quantum dot layer 230 and heat-treating at 100 ° C to 200 ° C, for example, 120 ° C. In addition, the second charge transport layer 235 made of poly-TPD may be UV treated to become hydrophilic. As described above, when the second charge transport layer 235 is made of a polymer material, the polymer material is highly resistant to harmful substances such as oxygen or moisture, and thus the life of the quantum dot light emitting device 200 may be increased. In addition, the turn-on voltage which is an operation start voltage of the quantum dot light emitting device 200 may be lowered. Meanwhile, a hole injection layer (HIL, not shown) may be further provided between the second graphene 240 and the second charge transport layer 235.

The second graphene 240 may be provided on the second charge transport layer 235. Here, the second graphene 240 may be p-type graphene 240. The second graphene 240 may be used as a p-type electrode of the quantum dot light emitting device 200. The p-type graphene 240 is doped with at least one graphene sheet with a p-type dopant. That is, the p-type graphene 240 may be formed by injecting and adsorbing the p-type dopant to the graphene sheet. The p-type dopant may be, for example, oxygen (O), gold (Au), bismuth (Bi), or the like, but is not limited thereto. Meanwhile, the thickness of the second graphene 240 may be about 0.34 nm, and may have a structure in which a plurality of graphenes are stacked. Since the thickness of the second graphene 240 is thinner than the wavelength of light generated in the graphene quantum dot layer 230, total reflection may not occur at the interface between the two layers.

A second contact pad 255 may be provided on the second graphene 240. The second contact pad 255 may inject holes into the second graphene 240. In the above description, the first and second graphenes 220 and 240 may be n-type and p-type graphene, respectively, but the first and second graphenes 220 and 240 may be p-type and n-type graphene, respectively. have. The graphene quantum dot light emitting device 200 according to the present exemplary embodiment may have improved light emission efficiency than the conventional quantum dot light emitting device, and may implement flexible light emitting devices using graphene to implement light emitting devices having various designs. In addition, since the graphene quantum dot is more durable than the conventional semiconductor-based quantum dot, the lifespan of the graphene quantum dot light emitting device 100 according to the present embodiment may be long.

FIG. 7 is a schematic example of an energy band structure of the graphene quantum dot light emitting device 200 illustrated in FIG. 6. The energy band structure of FIG. 7 includes an electron transport layer 225 made of TPBi, a graphene quantum dot layer 230, a hole transport layer 235 made of poly-TPD, and a p-type graph sequentially stacked on n-type graphene 220. An energy band structure of the graphene quantum dot light emitting device 200 including the fins 240.

Referring to FIG. 7, the highest occupied molecular level (HOMO) energy band level of the hole transport layer 235 is about 5.4 eV, and the balance band level of the graphene quantum dot layer 240 is about 6.2 eV. to be. As such, when the energy band level difference between the hole transport layer 235 and the graphene quantum dot layer 230, that is, the band offset is large, the efficiency of the light emitting device may be reduced. Such a band offset may reduce power efficiency due to an increase in turn-on voltage and an increase in operating voltage as well as a decrease in luminous efficiency. Therefore, in order to improve the performance of the graphene quantum dot light emitting device 200, it is necessary to reduce the band offset between the graphene quantum dot layer 230 and the hole transport layer 235. That is, as shown in FIG. 7, it is necessary to lower the energy band level of the graphene quantum dot layer 230. The graphene quantum dot light emitting device 200 according to the present exemplary embodiment may adjust the size and shape of the graphene quantum dots to reduce the band gap of the graphene quantum dot layer 230. Therefore, the luminous efficiency of the graphene quantum dot light emitting device 200 may be improved.

8A to 8D schematically illustrate light emission characteristics of the graphene quantum dot light emitting device 200 illustrated in FIG. 6.

Referring to FIG. 8A, as the voltage applied to the graphene quantum dot light emitting device 200 increases, the current density of the graphene quantum dot light emitting device 200 increases. In addition, it can be seen that the current density increases sharply from the moment when a voltage of about 10 V is applied to the graphene quantum dot light emitting device 200, which means that the turn-on voltage of the graphene quantum dot light emitting device 200 is about 10 V. It means.

Referring to FIG. 8B, as the magnitude of the voltage applied to the graphene quantum dot light emitting device 200 is increased, the emission luminance of the graphene quantum dot light emitting device 200 may be increased. In addition, it can be seen that the emission luminance increases rapidly from the moment when a voltage of about 10 V is applied to the graphene quantum dot light emitting device 200. This is because the turn-on voltage of the graphene quantum dot light emitting device 200 is about 10 V. Means.

FIG. 8C illustrates an external quantum efficiency (E.Q.E) with respect to the current density of the graphene quantum dot light emitting device 200. Referring to FIG. 8C, it can be seen that E.Q.E. of the graphene quantum dot light emitting device 200 is about 0.3%.

FIG. 8D illustrates the EL (electroluminescence) intensity of the emission wavelength of the graphene quantum dot light emitting device 200. Referring to FIG. 8D, the graphene quantum dot light emitting device 200 may exhibit sky blue light emission characteristics and may have a relatively wide half width.

11A to 11D schematically illustrate light emission characteristics of the graphene quantum dot light emitting device according to the first to third experimental examples. Here, the graphene quantum dot light emitting device according to the first to the third experimental example includes a hole transport layer made of poly-TPD. In addition, the graphene quantum dot layer of the first experimental example includes a plurality of graphene quantum dots, and the graphene quantum dot layer of the second experimental example includes a plurality of graphene quantum dots and PEO having a molecular weight of about 40,000. In addition, the graphene quantum dot layer of Experimental Example 3 includes a plurality of graphene quantum dots and PEO having a molecular weight of about 500,000.

Referring to FIG. 11A, as the magnitude of the voltage applied to the graphene quantum dot light emitting devices of the first to third experimental examples increases, the current density of the graphene quantum dot light emitting devices of each experimental example increases. The increase rate of the current density of each test example is different because the amount of PEO contained in the graphene quantum dot layer of each test example is different.

Referring to FIG. 11B, as the magnitude of the voltage applied to the graphene quantum dot light emitting devices of the first to third experimental examples is increased, the emission luminance of the graphene quantum dot light emitting devices of each experimental example increases. . The increase rate of the light emission luminance of each experimental example is different because the amount of PEO included in the graphene quantum dot layer of each experimental example is different.

FIG. 11C shows an external quantum efficiency (E.Q.E) with respect to the current density of the graphene quantum dot light emitting devices of the first to third experimental examples, respectively. Referring to FIG. 11C, it can be seen that the external quantum efficiency of the graphene quantum dot light emitting device of each experimental example varies depending on the amount of PEO included in the graphene quantum dot layer.

Fig. 11D shows EL intensities for emission wavelengths of the graphene quantum dot light emitting devices of the first to third experimental examples. Referring to FIG. 11D, it can be seen that the graphene quantum dot light emitting devices of the first to third experimental examples show light emission characteristics of the sky blue series and have a relatively wide half width. However, according to the amount of PEO contained in the graphene quantum dot layer, it can be seen that the EL intensity of the graphene quantum dot light emitting device of each experimental example is different.

12A to 12D schematically illustrate light emission characteristics of the graphene quantum dot light emitting devices according to the fourth to sixth experimental examples. Here, the graphene quantum dot light emitting device according to the fourth to sixth examples includes a hole transport layer made of TFB. In addition, the graphene quantum dot layer of Example 4 includes a plurality of graphene quantum dots, and the graphene quantum dot layer of Example 5 includes a plurality of graphene quantum dots and PEO having a molecular weight of about 40,000. In addition, the graphene quantum dot layer of Experimental Example 6 includes a plurality of graphene quantum dots and PEO having a molecular weight of about 500,000.

Referring to FIG. 12A, it can be seen that as the magnitude of the voltage applied to the graphene quantum dot light emitting devices of the fourth through sixth examples increases, the current density of the graphene quantum dot light emitting devices of each experimental example increases. The increase rate of the current density of each test example is different because the amount of PEO contained in the graphene quantum dot layer of each test example is different.

12B, it can be seen that as the magnitude of the voltage applied to the graphene quantum dot light emitting devices of Experiments 4 to 6 increases, the luminance of light emission of the graphene quantum dot light emitting devices of each Experimental Example increases. . The increase rate of the light emission luminance of each experimental example is different because the amount of PEO included in the graphene quantum dot layer of each experimental example is different.

FIG. 12C illustrates an external quantum efficiency (E.Q.E) with respect to the current density of the graphene quantum dot light emitting devices of the fourth through sixth examples, respectively. Referring to FIG. 12C, it can be seen that the external quantum efficiency of the graphene quantum dot light emitting device of each experimental example varies according to the amount of PEO included in the graphene quantum dot layer.

12D shows EL intensities for emission wavelengths of the graphene quantum dot light emitting devices of the fourth to sixth experimental examples. 12D, it can be seen that the graphene quantum dot light emitting devices of the fourth through sixth examples show light emission characteristics of the sky blue series and have a relatively wide half width. However, according to the amount of PEO contained in the graphene quantum dot layer, it can be seen that the EL intensity of the graphene quantum dot light emitting device of each experimental example is different. Therefore, by adjusting the amount of PEO included in the graphene quantum dot layer, it is possible to control the light emission characteristics of the graphene quantum dot light emitting device.

Next, a method of manufacturing the graphene quantum dot light emitting devices 100 and 200 according to an embodiment of the present invention will be described.

9A to 9F schematically illustrate steps of a method of manufacturing the graphene quantum dot light emitting device 100 according to an embodiment of the present invention.

Referring to FIG. 9A, the first graphene 20 may be formed on the substrate 10. First, at least one graphene sheet may be formed on the substrate 10 using chemical vapor deposition (CVD), mechanical or chemical exfoliation, epitaxial growth, or the like. The graphene sheet may be doped with the first dopant. Here, the first dopant may be an n-type dopant, and may include, for example, nitrogen (N), fluorine (F), and manganese (Mn). However, it is not limited thereto. The n-type dopant may be injected and adsorbed onto the graphene sheet to form the n-type graphene 20. Meanwhile, the substrate 10 may be removed after the first graphene 20, the graphene quantum dot layer 30, and the second graphene 30 are formed thereon. Alternatively, in the method for manufacturing the graphene quantum dot light emitting device 100 according to the present embodiment, the first graphene 20 may be used as a substrate without a separate substrate 10.

Next, referring to FIG. 9B, the graphene quantum dot layer 30 may be formed on the first graphene 20. The graphene quantum dot layer 30 may be formed by spin coating a plurality of graphene quantum dots on the first graphene 20. The graphene quantum dots may be formed by pulverizing the graphene or graphite by applying ultrasonic waves to a solution containing graphene or graphite.

On the other hand, the graphene quantum dot layer 30 by using a chemical vapor deposition (chemical vapor deposition, CVD), mechanical or chemical exfoliation method, epitaxy growth method, etc. on the first graphene 20 After forming, by applying a plasma impact to the graphene, the graphene may be formed by grinding into nano pieces.

In addition, the graphene quantum dots may be formed by heating graphene oxide or graphite oxide and reducing the cut portion of the graphene oxide or graphite oxide. Here, the oxidation and reduction process of graphene or graphite may be repeated two or more times, several times, and thus may control the size and shape of the graphene quantum dots. In addition, it is possible to reduce van der Waals attraction in graphene or graphite through the oxidation and reduction process of graphene or graphite. The size of the graphene quantum dots may be, for example, about 1 nm to about 30 nm, or about 1 nm to about 20 nm, more specifically 1 nm to 10 nm. Graphene quantum dots of the desired size can be filtered through dialysis. On the other hand, the graphene quantum dot formed as described above may be further coupled to the functional group on the surface (edge). An amine-based functional group may be attached to the graphene quantum dots. For example, alkylamine, aniline, or PEG may be attached to the graphene quantum dots.

Referring to FIG. 9C, a second graphene 40 may be formed on the graphene quantum dot layer 30. Chemical vapor deposition of at least one graphene sheet on the graphene quantum dot layer 30 is performed. deposition, CVD), mechanical or chemical exfoliation, epitaxial growth, and the like. The graphene sheet may be doped with a second dopant. Here, the second dopant may be a p-type dopant, and may include, for example, oxygen (O), gold (Au), bismuth (Bi), or the like. However, it is not limited thereto. The p-type dopant may be injected into and adsorbed to the graphene sheet to form the p-type graphene 20. In the above description, the first and second graphenes 20 and 40 may be n-type and p-type graphene, respectively, but the first and second graphenes 20 and 40 may be p-type and n-type graphene, respectively. have.

Referring to FIG. 9D, first and second contact pads 50 and 55 may be formed. The first contact pad 50 may be formed on the first graphene 20 to be spaced apart from the graphene quantum dot layer 30 and the second graphene 40. That is, the first contact pad 50 mesa etches the graphene quantum dot layer 30 and the second graphene 40, and is on the first graphene 20 exposed by the mesa etching. Can be formed. In addition, the second contact pads 55 may be formed on the second graphene 40. The method for manufacturing the graphene quantum dot light emitting device 100 according to the present exemplary embodiment replaces a compound semiconductor requiring expensive metal-organic chemical vapor deposition (MOCVD) equipment, and thus, conventional chemical vapor deposition (Chemical). It is possible to manufacture by Vapor Deposition (CVD) equipment, which can lower the manufacturing cost and shorten the process time compared to the conventional compound semiconductor light emitting device.

Meanwhile, the first and second contact pads 50 and 55 illustrated in FIG. 9D may be formed as follows. Referring to FIG. 9E, when a conductive substrate is used as the substrate 10, the first contact pad 50 may include a bottom surface of the substrate 10, that is, a surface on which the first graphene 20 of the substrate 10 is formed. It can be formed in the surface which faces. In addition, the second contact pads 55 may be formed on the second graphene 40.

In addition, referring to FIG. 9F, the first contact pad 50 removes the substrate 10, and the lower surface of the first graphene 20, that is, the graphene quantum dot layer 30 of the first graphene 20 is removed. ) May be formed on the side facing the formed side. In addition, the second contact pads 55 may be formed on the second graphene 40.

10A to 10F schematically illustrate steps of a method of manufacturing the graphene quantum dot light emitting device 200 according to another embodiment of the present invention.

Referring to FIG. 10A, the first graphene 220, the first charge transport layer 225, the graphene quantum dot layer 230, the second charge transport layer 235, and the second graph may be sequentially formed on the substrate 210. Fin 240 may be formed.

The first graphene 220 may be formed by forming at least one graphene sheet on the substrate 210 and doping with the first dopant. Here, the first dopant may be an n-type dopant, and may include, for example, nitrogen (N), fluorine (F), and manganese (Mn). Therefore, the first graphene 220 may be n-type graphene 220. Meanwhile, the substrate 210 forms a first graphene 220, a first charge transport layer 225, a graphene quantum dot layer 230, a second charge transport layer 235, and a second graphene 240 thereon. It may be removed later. Alternatively, in the method for manufacturing the graphene quantum dot light emitting device 200 according to the present embodiment, the first graphene 220 may be used as a substrate without a separate substrate 210. After the first graphene 220 is formed, it may be dried by heating in a nitrogen oven.

Next, the first charge transport layer 225 may be formed on the first graphene 220. The first charge transport layer 225 may be an electron transport layer (ETL). The first charge transport layer 225 may be formed by, for example, spin coating or depositing TPBi, PBD, BCP, BAlq, or OXD7 on the first graphene 220. The first charge transport layer 225 may be heat treated for drying or curing. In addition, the first charge transport layer 225 may be UV treated to increase the hydrophilicity of the surface thereof, so that a solution including graphene quantum dots may be easily deposited on the surface of the first charge transport layer 225.

In addition, the graphene quantum dot layer 230 may be formed on the first charge transport layer 225. The graphene quantum dot layer 230 may be formed by spin coating a solution including a plurality of graphene quantum dots on the first charge transport layer 225. In addition, the solution may further include an organic solvent, for example, polyethylene oxide (PEO), PES and the like.

The graphene quantum dots may be formed by pulverizing the graphene or graphite by applying ultrasonic waves to a solution containing graphene or graphite. Meanwhile, the graphene quantum dot layer 230 may form a graphene sheet on the first graphene 220 and apply a plasma impact to the graphene sheet, thereby forming the graphene sheet by pulverizing it into nano pieces. .

In addition, the graphene quantum dots may be formed by heating graphene oxide or graphite oxide and reducing the cut portion of the graphene oxide or graphite oxide. Here, the oxidation and reduction process of graphene or graphite may be repeated two or more times, several times, and thus may control the size and shape of the graphene quantum dots. In addition, it is possible to reduce van der Waals attraction in graphene or graphite through the oxidation and reduction process of graphene or graphite. The size of the graphene quantum dot may be, for example, about 1 nm to 20 nm, more specifically 1 nm to 10 nm. Graphene quantum dots of the desired size can be filtered through dialysis. On the other hand, the graphene quantum dot formed as described above may be further coupled to the functional group on the surface (edge). An amine-based functional group may be attached to the graphene quantum dots. For example, alkylamine, aniline, or PEG may be attached to the graphene quantum dots.

The second charge transport layer 235 may be formed on the graphene quantum dot layer 230. The second charge transport layer 235 may be a hole transport layer (HTL). The second charge transport layer 235 is a graphene quantum dot, for example, poly-TPD, PEDOT, PSS, PPV, PVK, TFB, PFB, TBADN, NPB, Spiro-NPB, DMFL-NPB, DPFL-NPB, mHOST5, etc. It may be formed by spin coating or depositing on layer 230. The second charge transport layer 235 may be heat treated for drying or curing. In addition, the second charge transport layer 235 may be UV treated to increase the hydrophilicity of the surface thereof, and thus, a solution including graphene quantum dots may be easily deposited on the surface of the second charge transport layer 235.

Finally, the second graphene 240 may be formed on the second charge transport layer 235. The second graphene 240 may be formed by forming at least one graphene sheet on the second charge transport layer 235 and doping it with a second dopant. After forming the second graphene 240, it may be dried by heating in a nitrogen oven. Here, the second dopant may be a p-type dopant, and may include, for example, oxygen (O), gold (Au), bismuth (Bi), or the like. In the above description, the first and second graphenes 220 and 240 may be n-type and p-type graphene, respectively, but the first and second graphenes 220 and 240 may be p-type and n-type graphene, respectively. have.

Referring to FIG. 10B, first and second contact pads 250 and 255 may be formed. The first contact pad 250 is spaced apart from the first charge transport layer 225, the graphene quantum dot layer 230, the second charge transport layer 235, and the second graphene 240 on the first graphene 220. Can be formed. That is, the first contact pad 250 mesa etches the first charge transport layer 225, the graphene quantum dot layer 230, the second charge transport layer 235, and the second graphene 240, It may be formed on the first graphene 220 exposed by the mesa etching. In addition, the second contact pads 255 may be formed on the second graphene 240. The method for manufacturing the graphene quantum dot light emitting device 200 according to the present embodiment replaces a compound semiconductor requiring expensive metal-organic chemical vapor deposition (MOCVD) equipment, and conventional chemical vapor deposition (Chemical) It is possible to manufacture by Vapor Deposition (CVD) equipment, which can lower the manufacturing cost and shorten the process time compared to the conventional compound semiconductor light emitting device.

Meanwhile, the first contact pad 250 illustrated in FIG. 10B may be formed as follows. Referring to FIG. 10C, when a conductive substrate is used as the substrate 210, the first contact pad 250 may include a bottom surface of the substrate 210, that is, a surface on which the first graphene 220 of the substrate 210 is formed. It can be formed in the surface which faces. In addition, referring to FIG. 10D, the first contact pad 250 removes the substrate 210, and the lower surface of the first graphene 220, that is, the first charge transport layer 225 of the first graphene 220. ) May be formed on the side facing the formed side.

Such a graphene quantum dot light emitting device and a method of manufacturing the same have been described with reference to the embodiments shown in the drawings for clarity, but these are merely exemplary, and those skilled in the art can various modifications and It will be appreciated that other equivalent embodiments are possible. Therefore, the true technical protection scope of the present invention will be defined by the appended claims.

10, 210: substrate 20, 220: first graphene
30, 230: graphene quantum dot layer 35, 36, 37: graphene quantum dot
40, 240: second graphene
50, 55, 250, 255: first and second contact pads
225: first charge transport layer 235: second charge transport layer
100, 200: graphene quantum dot light emitting device

Claims (23)

First graphene;
A graphene quantum dot layer provided on the first graphene and having a plurality of graphene quantum dots; And
Graphene quantum dot light emitting device comprising a; second graphene provided on the graphene quantum dot layer. The method of claim 1,
The first graphene is n-type graphene, the second graphene is a graphene quantum dot light emitting device of p-type graphene. The method of claim 2,
The graphene quantum dot light emitting device further comprises an electron transport layer (ETL) provided between the n-type graphene and the graphene quantum dot layer. The method of claim 3, wherein
The electron transport layer is a graphene quantum dot light emitting device including TPBi, PBD, BCP, BAlq or OXD7. The method of claim 2,
A graphene quantum dot light emitting device further comprising a hole transport layer (HTL) provided between the graphene quantum dot layer and the p-type graphene. The method of claim 5, wherein
The hole transport layer is a graphene quantum dot light emitting device including poly-TPD, PEDOT, PSS, PPV, PVK, TFB, PFB, TBADN, NPB, Spiro-NPB, DMFL-NPB, DPFL-NPB or mHOST5. The method of claim 1,
The graphene quantum dot layer is a graphene quantum dot light emitting device further comprising an organic solvent. The method of claim 1,
The graphene quantum dot light emitting device having a size of the plurality of graphene quantum dots is 1 to 30 nm. The method of claim 2,
The n-type graphene is a graphene quantum dot light emitting device of graphene doped with one selected from nitrogen (N), fluorine (F) and manganese (Mn). The method of claim 2,
The p-type graphene is a graphene quantum dot light emitting device of graphene doped with one selected from oxygen (O), gold (Au) and bismuth (Bi). The method of claim 1,
The graphene quantum dot light emitting device further comprising a first contact pad provided on the first graphene spaced apart from the graphene quantum dot layer and the second graphene, or provided on the lower surface of the first graphene. The method of claim 1,
A graphene quantum dot light emitting device further comprising a second contact pad provided on the second graphene. Forming a first graphene doped with a first dopant;
Forming a graphene quantum dot layer having a plurality of graphene quantum dots on the first graphene; And
Forming a second graphene doped with a second dopant on the graphene quantum dot layer; manufacturing method of a graphene quantum dot light emitting device comprising a. The method of claim 13,
The first dopant is an n-type dopant, the second dopant is a p-type dopant manufacturing method of a graphene quantum dot light emitting device. The method of claim 14,
The n-type dopant is a method of manufacturing a graphene quantum dot light emitting device is one selected from nitrogen (N), fluorine (F) and manganese (Mn). The method of claim 14,
The p-type dopant is a method of manufacturing a graphene quantum dot light emitting device is one selected from oxygen (O), gold (Au) and bismuth (Bi). The method of claim 14,
And forming an electron transport layer (ETL) between the first graphene and the graphene quantum dot light emitting layer. The method of claim 17,
The electron transport layer is a method of manufacturing a graphene quantum dot light emitting device including TPBi, PBD, BCP, BAlq or OXD7. The method of claim 14,
Forming a hole transport layer (HTL) between the graphene quantum dot light emitting layer and the second graphene further manufacturing method of a graphene quantum dot light emitting device. The method of claim 19,
The hole transport layer is a method of manufacturing a graphene quantum dot light emitting device comprising poly-TPD, PEDOT, PSS, PPV, PVK, TFB, PFB, TBADN, NPB, Spiro-NPB, DMFL-NPB, DPFL-NPB or mHOST5. The method of claim 13,
The graphene quantum dot is a graphene quantum dot manufacturing method of the graphene quantum dot light emitting device is formed by grinding the graphite by applying an ultrasonic wave to a solution containing graphite (graphite). The method of claim 13,
The plurality of graphene quantum dot is a method of manufacturing a graphene quantum dot light emitting device is formed by heating the graphite oxide to reduce a portion, and cutting the reduced portion of the graphite oxide. The method of claim 13,
The graphene quantum dot layer is a method for manufacturing a graphene quantum dot light emitting device is formed by spin coating the plurality of graphene quantum dots on the first graphene.

Images