KR20130078043A - Organic electroluminescence element including graphene oxide as hole transport layer - Google Patents

Abstract

PURPOSE: An organic electroluminescence element including graphene oxide as a hole transport layer is provided to increase luminous efficiency by blocking electron transfer. CONSTITUTION: A hole transport layer is formed on an anode. A light emitting layer is formed on the hole transport layer. An electron transport layer is formed on the light emitting layer. A cathode layer is formed on an electron injection layer. The thickness of the hole transport layer is 3 to 5 nm.

Description

Organic Electroluminescence Element Including Graphene Oxide as Hole Transport Layer}

The present invention relates to an organic electroluminescent (organic EL) device comprising graphene oxide as a hole transport layer.

In recent years, research for the practical use of organic electroluminescent element (henceforth organic electroluminescent element) is performed actively. It is expected that the organic EL device can realize a high current density at low voltage, and thus can realize high light emission brightness and light emission efficiency. The organic EL element is provided with a first electrode and a second electrode sandwiching the organic EL layer, and the electrode on the side from which light is taken out is required to have high transmittance. As such an electrode material, an oxide transparent conductive film (TCO) material (for example, indium tin oxide (ITO), indium zinc oxide (IZO), indium tungsten oxide (IWO), etc.) is usually used. It is becoming. Since these materials have a relatively large work function of ˜5 eV, they are used as hole injection electrodes (anodes) for organic materials.

Light emission of the organic EL element is measured by holes injected into the highest occupied molecular orbital (HOMO, generally measured as ionization potential) of the light emitting layer material, and the lowest non-occupied molecular orbital (LUMO, generally measured as electron affinity). It is obtained by emitting light when the excitation energy of excitons generated by the electrons injected into it is relaxed. In general, the organic EL device has a laminated structure having some or all of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer in addition to the light emitting layer in order to efficiently perform hole injection and electron injection into the light emitting layer. do.

Poly (styrenesulfonate) -doped poly (3,4-ethylenedioxythiophene (PEDOT: PSS) is a compound that has been widely used as a hole transport layer (HTL), but the high acidity of the PEDOT: PSS solution It gradually erodes the ITO electrode and greatly reduces the overall device efficiency and long-term stability, and even though PEDOT: PSS has excellent electrical conductivity, quenching of excitons is easy between PEDOT: PSS and the surface of the emitting layer. It happens.

Recently, metal oxides replacing PEDOT: PSS are MoO ₃ , WO ₃ , NiO, V ₂ O ₅ and Fe ₃ O ₄ Has been proposed as an effective charge carrier, but the low molecular weight material has to go through a dry process using vacuum equipment such as thermal evaporation or vapor phase deposition. Therefore, there is a need for a study of a new hole transport layer (HTL) material that replaces PEDOT: PSS and to which a simpler wet process can be applied.

Therefore, in order to solve the above problems, the present invention can be prepared organic EL by a wet process such as rotary coating, printing after dissolving in a suitable solvent, and provides an excellent hole transport layer (HTL) material than the conventional PEDOT: PSS I would like to.

The present invention is an organic EL (Electroluminescence) device comprising a hole transport layer, a light emitting layer and an electron transport layer between the anode and the cathode, the hole transport layer is characterized in that the graphene oxide (graphene oxide). An organic electroluminescence (EL) device is provided.

In addition, the present invention is a method of manufacturing an organic EL (Electroluminescence) device comprising a hole transport layer, a light emitting layer and an electron transport layer between the anode and the cathode,

Dropping a negatively charged graphene oxide solution at a pH of 2-4 on a positive electrode substrate; And spin coating for 20 to 60 seconds at 2000 to 4000 rpm after 1 to 5 minutes of dripping; It provides a method for manufacturing an organic EL device comprising a.

The graphene oxide thin film according to the present invention effectively blocks electron transfer, reduces the quenching of excitons between the light emitting layer and the hole transport layer, and facilitates hole-electron recombination in the light emitting layer, thereby emitting light in the organic EL device. The efficiency can be increased. Therefore, the EL element including the graphene oxide thin film according to the present invention as an electron transport layer can be usefully used for a flat panel display or a light source for illumination.

Figure 1 (a) shows a schematic diagram of the structure of the PLED of the present invention and the structural formula of graphene oxide, (b) is an energy diagram for the flat band conditions of various hole transport layers (rGO, GO and PEDOT: PSS).
FIG. 2 is an atomic force microscopy (AFM) photograph of four GO thin films on a substrate. FIG. (a) is a spin-coated GO thin film once, (b) is a spin-coated GO thin film twice, (c) is a spin-coated GO thin film six times, and (d) is a spin-coated GO thin film ten times.
3 is a graph of the characteristics of a PLED investigated with various GO layers with or without rGO and PEDOT: PSS, where (a) is a graph of current density versus applied voltage (JV). (b) is a graph of luminance versus applied voltage (LV), (c) is a graph of luminous efficiency versus voltage (EV) and (d) is a graph of luminous efficacy (luminous efficacy) versus voltage (LE-V).
4 shows the results of an ultraviolet photoemission spectroscopy (UPS) measurement test. (a) is the inelastic cut-off area, (b) the Fermi boundary, (c) the OPV structure, and (d) the JV characteristics of the OPV.
Fig. 5 (a) and (b) are the EL spectra of the structure and the device of the PLED for explaining the electron-blocking aspect of the GO layer of the present invention, (c) is the photoluminescence (PL) ) Experimental results, and (d) is the optical transmission spectrum for GO layers of various thicknesses located on ITO / glass substrates.

The present invention is an organic EL (Electroluminescence) device comprising a hole transport layer, a light emitting layer and an electron transport layer between the anode and the cathode, the hole transport layer is an organic EL (Electroluminescence) device, characterized in that the graphene oxide (graphene oxide). To provide.

In one embodiment of the present invention, the organic EL device is an anode; A hole transporting layer formed on the anode; An emission layer formed on the hole transport layer; An electron transport layer formed on the light emitting layer; And it may include a cathode layer formed on the electron injection layer.

In order to take out light emission from an organic EL element out of the element, it is preferable that either or both of the anode and the cathode are made to be light transmissive. The stacking order of each layer of the organic EL element and which electrode to make light transmissive can be selected according to the use of the organic EL element.

As described above, the anode used in the present invention may be light transmissive or light reflective. In the case of making it transparent, transparent conductive oxide materials such as ITO (indium tin oxide), IZO (indium zinc oxide), IWO (indium tungsten oxide), and AZO (Al-doped zinc oxide) are generally known. It can be used to form an anode. In order to reduce the electrical resistance of the anode wiring and to control the reflection or transmittance, the anode may be a laminated structure of a thin (about 50 nm) metal material and the above-mentioned transparent conductive film.

When forming a light reflective anode, a highly reflective metal, an amorphous alloy or a microcrystalline alloy, or a laminate of these and the above-mentioned transparent conductive film can be used. Metals with high reflectivity include Al, Ag, Ta, Zn, Mo, W, Ni, Cr and the like. Amorphous alloys of high reflectivity include NiP, NiB, CrP, CrB and the like. The high reflectivity microcrystalline alloy includes NiAl, silver alloy, and the like. A transparent conductive oxide, a metal with high reflectance, an amorphous alloy or a microcrystalline alloy can be formed by any method known in the art, such as a vapor deposition method and a sputtering method.

In addition, it is preferable that the cathode has a metal, an alloy, an electrically conductive compound and a mixture thereof having a small work function as the electrode material. Specific examples include sodium, sodium-potassium alloys, magnesium, lithium, magnesium silver alloys, aluminum / aluminum oxides, aluminum lithium alloys, indium, rare earth metals, and the like. The said cathode can be manufactured by forming a thin film using these electrode materials by methods, such as vapor deposition and sputtering. When light emission from the light emitting layer is taken out from the cathode side, light transmittance can be improved by using a laminated structure of the oxide transparent conductive material introduced as the metal, alloy and anode material as the cathode.

In one embodiment of the present invention, the graphene oxide hole transport layer is formed on the anode, the hole transport layer is a negatively charged graphene oxide (graphene oxide) solution of pH 2 to 4 or pH 3 to 4 on the anode substrate It can be formed by coating.

The hole aqueous layer may have a thickness of 3 nm to 5 nm or 3.5 to 4.7 nm. If the thickness is 5 nm or more, the contact resistance may be increased by low hole injection / movement. If the thickness is less than 3 nm, the electron blocking and hole transport efficiency may be reduced. Can be.

The material of the light emitting layer used for this invention can be selected according to a desired color tone. For example, to obtain light emission from blue to cyan, fluorescent brighteners such as benzothiazole, benzoimidazole and benzoxazole, styrylbenzene compounds, aromatic dimethylidene compounds and the like can be used. Can be. Specifically, ADN, 4,4'-bis (2,2'-diphenylvinyl) biphenyl (DPVBi), 2-methyl-9,10, di (2-naphthyl) anthracene (MADN) described above, 9,10-bis- (9,9-bis (n-propyl) fluoren-2-yl) anthracene (ADF), 9- (2-naphthyl) -10- (9,9-bis (n-propyl ) -Fluoren-2-yl) anthracene (ANF) and the like. In addition, the light emitting layer may be doped with a fluorescent dye. The fluorescent dye material to be used as the dopant can be selected according to the desired color tone. Specifically, fluorescent dye materials include conventionally known condensed ring derivatives such as perylene and rubrene, quinacridone derivatives and phenoxazone 660, 4. -(Dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM), 4- (dicyanomethylene) -6-methyl-2- [2- ( Julolidin 9-yl) ethyl] -4H-pyran (DCM2), 4- (dicyanomethylene) -2-methyl-6- (1,1,7,7-tetramethyljulolidyl ) -9-enyl) -4H-pyran (DCJT), 4- (dicyanomethylene) -2-t-butyl-6- (1,1,7,7-tetramethylzulolidil-9-enyl)- Dicyano methylene derivatives such as 4H-pyran (DCJTB), perynone, coumarin derivatives, pyrromethane derivatives, and cyanine pigments. In addition, luminescent polymers may be used, and more specifically, PPV (poly (p-phenylenevinylene)), PPP (poly (p-phenylene)), PT (polythiophene), polyfullerene, ladder-type polymer, phosphorescent series Polymers and derivatives thereof may be used, but are not limited thereto.

In addition, examples of the electron transport layer used in the present invention include alkali metal chalcogenides such as Li ₂ O, LiO, Na ₂ S, Na ₂ Se, and NaO, CaO, BaO, SrO, BeO, BaS, and CaSe. of the alkaline earth metal chalcogenides, LiF, NaF, KF, CsF , LiCl, an alkali metal halide such as KCl and _{NaCl, CaF 2, BaF 2,} SrF 2, MgF 2 and BeF halides of alkaline earth metal _2, and Alkali metal carbonates such as Cs ₂ CO ₃ may be used, but the present invention is not limited thereto. In addition, in the electron transport material, the film is also a negative electrode doped with alkali metals such as Li, Na, K, Cs, alkali metal halides such as LiF, NaF, KF, CsF, and alkali metal carbonates such as Cs ₂ CO ₃ as impurities. It can be used as an electron transport layer for promoting electron transport from the.

1A shows ITO (150 nm) as a transparent anode, graphene oxide (GO) as a hole transport layer (HTL), and poly (phenylvinylene) as an emissive layer: super yellow (SY (Merck Co., M _w = 1,950,000 g mol ^-1 )) (150 nm), LiF (1 nm) with electron injection / transport layer (EIL / ETL), Al (70 nm) with metal cathode) It is an embodiment of an organic EL device obtained by laminating in order, and the structure and the material are not limited thereto.

The present invention also provides a method of manufacturing an organic EL (Electroluminescence) device comprising a hole transport layer, a light emitting layer and an electron transport layer between an anode and a cathode,

Dropping a negatively charged graphene oxide solution at a pH of 2-4 on a positive electrode substrate; And spin coating for 20 to 60 seconds at 2000 to 4000 rpm after 1 to 5 minutes of dripping; It provides a method of manufacturing an organic EL device comprising a.

In one embodiment of the present invention, the step of inducing a hydrophilic surface by treating the positive electrode substrate with an oxygen plasma before dropping the graphene oxide may be further performed.

In another embodiment of the present invention, the dripping step and the coating step may be repeated 2 to 6 times for even coating, preferably 4 to 5 times, but is not limited thereto.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail with reference to the following examples. However, the following examples are intended to illustrate the contents of the present invention, but the scope of the present invention is not limited to the following examples. Embodiments of the present invention are provided to more fully describe the present invention to those skilled in the art.

< Experimental Example >

The following experimental examples are intended to provide experimental examples that are commonly applied to each embodiment according to the present invention.

One. GO ( Graphene oxide Manufacturing

Graphene oxide was synthesized by the modified Hummers method and stripped under sonication conditions to obtain a brown dispersion. Graphene oxide (GO) obtained was negatively charged under a wide range of pH conditions because the GO sheet has a chemical functional group such as carboxylic acid.

2. rGO Manufacturing

GO solution (10.0 ml, 0.50 mg / ml) was mixed with 10.0 μl of hydrazine solution (35 wt% in water, Aldrich) and 70 μl of ammonia solution (30%, Samchun). After stirring for 10 minutes, the reaction mixture was heated to 95 ℃ for 1 hour, thereby producing a reduced graphene oxide (rGO) solution.

3. PLED  And PSC  Produce

Two devices (PLED, PSC) were fabricated on patterned ITO-coated glass substrates. The glass substrate was washed by sonication in acetone and isopropyl alcohol and drying in nitrogen steam.

A negatively charged graphene oxide (GO) solution of pH 3.3 (0.5 mg mL ^-1 ) was loaded after the oxygen plasma process to make the surface of the ITO substrate hydrophilic. The dropped GO was maintained for 2 minutes, and then spin coated at 3000 rpm for 30 seconds. The process was repeated until all of the GO sheets were coated.

For the production of PLED, a super yellow (SY) solution of Merck, a poly (p-phenylenevinylene) -based luminescent polymer, was dissolved in chlorobenzene (0.7 wt%), which was spun on the GO thin plate at 2000 rpm for 45 seconds. After casting, annealing at 80 ° C. for 30 minutes to prepare a PLED including an SY layer having a thickness of 150 nm. Finally, a 1 nm LiF layer and a 70 nm-thick Al layer were thermally deposited on the SY layer to form a PLED.

To prepare the PSC, the P3HT solution was dissolved in chlorobenzene (1.0 wt%), spin cast it on the GO layer at 700 rpm for 60 seconds, and then annealed at 150 ° C. for 10 minutes to prepare a PSC including a 100 nm thick P3HT layer. It was. Thereafter, a 70 nm-thick Al layer was thermally deposited on the P3HT layer to complete the preparation of the PSC.

4. PLED  Device characteristic investigation

The applied current density and luminance characteristics were measured using a Keithley 2400 source measurement unit and a Konica Minolta spectroradiometer (CS-2000).

5. PSC  Device characteristic investigation

Measurements were performed using a high performance optical fiber for induction of light from a solar simulator of Keithley 2635A source measurement unit with solar cells in a glove box. JV curves for the device were measured under AM 1.5G illumination at 100 mW / cm ² .

6. PLED Investigation of electron blocking effect

PLED devices were manufactured according to the PLED manufacturing method. The SPR-01 solution was also dissolved in chlorobenzene (1.4 wt%) and spin-cast on ITO at 2000 rpm for 45 seconds, after which a simple UV / O ₃ treatment was performed for GO film formation on the polymer surface.

7. Characteristic investigation

Surface roughness and thickness of GO / Si were measured by AFM (Veeco, USA). UV-Vis spectrometer (Varian Cary 5000) was used to investigate the optical transmission of ITO, ITO / PEDOT: PSS and GO / ITO. PL intensities of SY (10 nm) / quartz, SY (10 nm) / PEDOT: PSS / quartz and SY (10 nm) / GO / quartz were measured by photoluminescence spectroscopy (EDINBURGH INSTRUMENT LTD).

< Example  1> PLED  And PSC  Manufacturing and Characteristic Review

1 shows a schematic diagram of a PLED device using a negative phone GO. PLED is ITO (150 nm) as transparent anode, GO as HTL, poly (phenylvinylene) as emissive layer: super yellow (SY (Merck Co., M _w = 1,950,000 g mol ^-1 ) (150 nm), LiF (1 nm) is deposited using an electron injection / transport layer (EIL / ETL), and Al (70 nm) is sequentially stacked with a metal cathode. The chemical structure of negatively charged GO has chemical functional groups such as carboxyl, hydroxyl and epoxy groups. Functional groups such as epoxy and hydroxy groups are sp ² of hexagonal graphene lattice on the base plate. Disrupts conjugation. Thus, GO acts as an insulator with a wide bandgap of about 3.6 eV. The Fermi level of GO of the present invention by ultraviolet photoelectron spectroscopy (UPS) measurement was found to be about 4.89 eV, while the Fermi level of rGO was found to be 4.79 eV (see FIGS. 4 a, b). Reduction of GO removes the functionalities of the GO sheet, resulting in partial recovery of sp2 conjugation, thus reducing the bandgap to 1.15 eV. RGO with reduced bandgap is different from the GO layer of PLED.

FIG. 2 is an atomic force microscopy (AFM) photograph of four GO thin films on a substrate. FIG. (a) is a spin-coated GO thin film once, (b) is a spin-coated GO thin film twice, (c) is a spin-coated GO thin film six times, and (d) is a spin-coated GO thin film ten times. Morphological analysis and thickness of the GO thin film depended on the number of spin-coated. It was found difficult to cover both the GO thin film on the ITO substrate with one or two spin-coatings. Repeated spin coating resulted in the complete formation of the GO thin film. The average thickness of the GO thin films spin-coated 6 and 10 was about 4.3 nm and 5.3 nm, respectively, as measured by ellipsometry. .

The characteristics of the PLEDs irradiated with rGO and PEDOT: PSS or with varying thicknesses of GO layers except PEDOT: PSS are shown in FIG. 3. (a) is a graph of current density versus applied voltage (JV), (b) is a graph of luminance versus applied voltage (LV), (c) is a graph of luminous efficiency versus voltage (EV) and (d) is a graph of luminous efficacy versus voltage (LE-V). All devices showed green emission of SY regardless of the type and voltage of HTL. PEDOT: PSS PLED was used as a reference group with a maximum luminescence of 33800 cd / m ² (at 12.6 V) and a maximum luminous efficiency of 8.7 cd / A (at 9.6 V). PLEDs composed of rCO layers showed a maximum emission of 8300 cd / m ² (at 13 V) and a maximum luminous efficiency of 5.0 cd / A (at 8.6 V), significantly lower than PEDOT: PSS PLEDs. This is believed to be due to the low conductivity of the rGO layer and the low hole injection due to the contact barrier between rGO and SY. On the other hand, PLEDs with GO layers showed increased EL efficiency and light emission. Among various GO layer thicknesses, PLEDs with 4.3 nm thick CO thin films showed a maximum luminous efficiency of 39000 cd / m ² (at 10.8 V) and a maximum luminous efficiency of 19.1 cd / A (at 6.8 V), PEDOT: Increased by about 220% and 280%, respectively, compared to PLEDs in PSS. In addition, the operating voltage of PLEDs composed of thin layer GO was almost the same as PLEDs of PEDOT: PSS and PLEDs of rGO layer, despite low electrical conductivity. Referring to the energy level diagram of FIG. 1B, electron-blocking of the GO thin film from SY to the ITO cathode was expected due to the wide bandgap, unlike rGO with a small bandgap. The electron-blocking effect has optimized the possibility of electron-hole coupling with the luminescent SY layer, and therefore the operation of the PLED and its efficiency have been shown to be good. However, as the thickness of the GO thin film became thicker, the operating efficiency decreased, which is believed to be due to an increase in contact resistance due to low hole injection / movement. More detailed characteristics of the PLED are shown in Table 1 below.

[Table 1]

To verify the energy levels of GO, rGO and PEDOT: PSS, UPS measurements were taken. The results are shown in Fig. From the difference between the inelastic cut-off (FIG. 4A) and the Fermi boundary (FIG. 4B), the work functions of GO, rGO and PEDOT: PSS were calculated. The PEDOT: PSS layer showed a work function of 4.95 eV, while the GO and rGO showed 4.89 and 4.79 eV, respectively. This means that using any of GO, rGO, and PEDOT: PSS with HTL, there was no significant change in the contact barrier (0.2 eV or less). Photovoltaic measurements were also performed to confirm the work function values by UPS measurements. The device structure of OPV is a sequential stack of ITO, PEDOT: PSS or GO, poly 3-hexylthiophene (P3HT, Merck Co., M _w = 75,000 g mol ^-1 , RR> 97%), and Al, Its schematic diagram is shown in c of FIG. 4. JV curves for the device were measured under AM 1.5G illumination at 100 mW / cm ² . Typically, V _oc of metal-insulator-metal (MIM) devices Was obtained from the difference in work function of the two metal contacts. In the OPV structure of the present invention, V _oc The difference in value was influenced by the work function difference of PEDOT: PSS and GO coated ITO while the work function of Al cathode was fixed. V _oc of OPV with GO The value (0.53 V) was found to be lower than in the case of PEDOT: PSS (0.66 V), which is shown in Figure 4 (d). Through the above results, the work function of GO as shown in Figure 1 (b) was confirmed by comparing with the work function of PEDOT: PSS.

< Example  2> PLED Review of Electronic Blocking Effects

5 (a) and 5 (b) show the EL spectrum of the structure and device of the PLED for explaining the electron-blocking aspect of the GO layer of the present invention. The device comprises two light-emitting polymer layers of SPR-001 (red light emitting polymer, Merck Co.) and SY (green light emitting polymer, Merck Co.), which are poly (p-phenylenevinylene) based light emitting polymers. do. The structure of SPR-001 is not known and it is difficult to successfully position it by spin coating a hydrophilic GO thin film on hydrophobic SPR-001 or SY in polymer / GO / polymer device structure. For coating of GO thin films, a brief UV / O ₃ treatment was performed on the polymer surface. The EL spectra for the prinstin and UV / O ₃ treated polymer thin films (SPR-011 or SY) were found to be nearly identical.

When the GO thin film is located between the SY and SPR-001 layers (ITO / SY / GO / SPR-001 / LiF / Al structure), red light is mainly emitted, as shown in FIG. See pink line in FIG. 5 (b)). On the other hand, in the device arranged in reverse, such as ITO / SPR-001 / GO / SY / LiF / Al, green light mainly emitted (see the blue line in FIG. 5 (b)). The results show that the GO thin film effectively prevents electron migration from the SY layer to the SPR-001 layer in the ITO / SPR-001 / GO / SY / LiF / Al structure, thereby preventing the recombination of the injection holes and electrons with the SY layer. It usually occurs. The EL spectrum appeared to overlap almost that of the device with the SY-only luminescent layer, showing that the effect of red light emission such as red shift is minimal but the electron blocking of the GO thin film is effectively achieved.

However, when the rGO thin film was located between the SY and SPR-001 layers (ITO / SPR-001 / GO / SY / LiF / Al structures), red light emission (gray line in Fig. 5 (b)) occurred mainly. This is because, as a result, the rGO thin film does not have an electron blocking effect.

Therefore, the above result shows that the GO thin film of the present invention effectively blocks electron migration and facilitates hole-electron recombination with the light emitting layer, thereby increasing the device efficiency of the PLED.

Photoluminescence (PL) measurement experiments also show the high efficiency of the device when using GO thin films. Among the PL intensities of SY thin films (10 nm), PEDOT: PSS / SY (10 nm) and GO / SY (10 nm) on quartz substrates, PEDOT: PSS showed the lowest value, which was PEDOT: PSS / This means that a significant amount of excitation electrons are quenched at the SY interface. However, PL suppression in the GO / SY thin film occurred lower than that of the PEDOT: PSS / SY thin film, which means that the GO layer reduces the inhibitory effect than that of the PEDOT: PSS / SY thin film. It is shown to 5 (c).

The optical transmission spectrum for GO layers of various thicknesses located on ITO / glass substrates is shown in FIG. 5 (d). The transmittance decreased slightly with increasing thickness, but there was no significant change in transparency and transparency of the thin GO coated anode substrate.

Having described the specific parts of the present invention in detail, it will be apparent to those skilled in the art that such specific descriptions are only preferred embodiments, and thus the scope of the present invention is not limited thereto. will be. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (8)

An organic electroluminescence (EL) device comprising a hole transport layer, a light emitting layer, and an electron transport layer between an anode and a cathode, wherein the hole transport layer is graphene oxide.
The method of claim 1,
The organic EL device is
anode;
A hole transport layer formed on the anode;
An emission layer formed on the hole transport layer;
An electron transport layer formed on the light emitting layer; And
An organic EL device comprising a cathode layer formed on the electron injection layer.
The method according to claim 1 or 2,
The thickness of the hole transport layer is an organic EL device, characterized in that 3nm to 5nm.
The method according to claim 1 or 2,
The thickness of the hole transport layer is an organic EL device, characterized in that 3.5 nm to 4.7 nm.
The method of claim 1,
The hole transport layer is an organic EL device, characterized in that formed by coating a negatively charged graphene oxide (graphene oxide) solution of pH 2 to 4 on the anode substrate.
In the method of manufacturing an organic EL (Electroluminescence) device comprising a hole transport layer, a light emitting layer and an electron transport layer between the anode and the cathode,
Dropping a negatively charged graphene oxide solution at a pH of 2-4 on a positive electrode substrate; And
Spin coating for 20 to 60 seconds at 2000 to 4000 rpm after 1 to 5 minutes of dripping; Method for producing an organic EL device comprising a.
The method according to claim 6,
And treating the anode substrate with an oxygen plasma prior to dropping the graphene oxide to induce a hydrophilic surface.
8. The method according to claim 6 or 7,
The method of manufacturing an organic EL device, characterized in that the dropping step and the coating step is repeated 2 to 6 times.

Images