KR101552662B1 - Light Emitting Device and Method Of Manufacturing Hole Injection/Transport layer - Google Patents

Abstract

The present invention provides a light emitting device. The light emitting device according to an embodiment of the present invention includes: a first electrode for receiving a first voltage on a base substrate; a light emitting layer placed on the first electrode; a second electrode placed on the light emitting layer for receiving a second voltage different from the first electrode; and a hole injection/transport layer placed between the first electrode and the light emitting layer for injecting a hole and delivering the hole. The hole injection/transport layer can include graphene or a graphene oxide, and a p-type nickel oxide (NiO).

Description

TECHNICAL FIELD [0001] The present invention relates to a light emitting device and a method of manufacturing a hole injecting / transporting layer for a light emitting device,

The present invention relates to a method of manufacturing a light emitting device and a hole injecting / transporting layer for a light emitting device.

Quantum dots based light-emitting diodes (QLEDs) can be used as conventional organic light-emitting diodes (OLEDs), have high quantum efficiency and excellent color purity. A conventional quantum dot light emitting device uses a material in which a hole injection layer is further doped with PEDOT: PSS or PEDOT: PSS such as DMF, DMSO and PFI. However, in such a case, there is a problem of the oxidation stability part as it is produced through synthesis of an organic material. In addition, poly-TPD and PVK having good conductivity can be selected as the hole transport layer, but the oxidation stability is also deteriorated due to the organic material.

An object of the present invention is to provide a light emitting device having excellent hole conductivity and excellent oxidation stability characteristics.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and the problems not mentioned can be clearly understood by those skilled in the art from the present specification and the accompanying drawings will be.

The present invention provides a light emitting device.

A light emitting device according to an embodiment of the present invention includes a first electrode for receiving a first voltage on a base substrate, a light emitting layer disposed on the first electrode, And a hole injecting / transporting layer positioned between the first electrode and the light emitting layer to inject holes and transfer holes, wherein the hole injecting / transporting layer is disposed between the first electrode and the light emitting layer, The implant / transport layer may comprise graphene or graphene oxide and p-type nickel oxide (NiO).

The hole injection / transport layer may be graphene or graphen oxide coordinated to the surface of nickel oxide (NiO).

The graphene can be synthesized by heating citric acid to a temperature of 200 to 500 degrees Celsius and then dispersing it in NaOH after the first hour.

The graphene oxide can be synthesized by heating citric acid to a temperature of 200 to 500 ° C and, after a second time, dispersing the mixture in NaOH.

The first time may be shorter than the second time.

The first time may be a time of 30 minutes to 1 hour and 30 minutes, and the second time may be a time of 1 hour and 30 minutes to 2 hours and 30 minutes.

The light emitting device may further include an electron transport layer disposed between the light emitting layer and the second electrode. The electron transport layer may include ZnO nanoparticles synthesized by dissolving a zinc compound and a basic substance in an alcohol solvent.

The HOMO level and / or the LUMO level of the light emitting device may be changed depending on the concentration of the alcohol solvent and the basic substance when synthesizing the ZnO nanoparticles, so that band gap leveling with the light emitting layer can be controlled.

The light emitting device may be interfaced with a polar or non-polar surfactant when synthesizing the ZnO nanoparticles.

The light emitting device may be doped with a metal material when synthesizing the ZnO nanoparticles.

According to an embodiment of the present invention, a light emitting device having excellent hole conductivity and excellent oxidation stability characteristics can be provided.

The effects of the present invention are not limited to the above-described effects, and the effects not mentioned can be clearly understood by those skilled in the art from the present specification and the accompanying drawings.

1 is a view illustrating a light emitting device according to an embodiment of the present invention.
FIG. 2 is a view showing a hole injection / transport layer. FIG.
FIG. 3 is a view showing an energy band gap of the light emitting device of FIG. 1;
4 is a view showing synthesis of a graphene quantum dot and a graphene oxide quantum dot.
5 is a view illustrating a light emitting device according to another embodiment.
6 is a view showing a process of synthesizing ZnO of FIG.
7 is a flowchart according to the synthesis method of FIG.
FIG. 8 shows the UV-visible absorption spectrum of the ZnO nanoparticles synthesized according to FIG.
FIG. 9 shows PL characteristics of ZnO synthesized according to FIG.
10 is an XRD result showing the crystal orientation of ZnO synthesized according to FIG.
11 is a TEM photograph of the ZnO nanoparticles synthesized according to FIG.
FIG. 12 is a view showing the size control and fluorescence characteristics of ZnO nanoparticles according to synthesis conditions. FIG.
13 is a graph showing the characteristics of the ZnO nanoparticles applied to the green quantum dot according to their sizes.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to be illustrative of the present invention and not to limit the scope of the invention. Should be interpreted to include modifications or variations that do not depart from the spirit of the invention. In addition, the terms used in the present specification and the accompanying drawings are for explaining the present invention easily, and thus the present invention is not limited by the terms used in the present specification and the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

In addition, the terms `first`,` second`, and the like in the present specification are used for the purpose of distinguishing one component from another component, not limiting. It is also to be understood that when a film, an area, a component, or the like is referred to as being "on" or "on" another part, .

Hereinafter, the light emitting device will be described using a quantum dot light emitting device as an example. However, the present invention is not limited to this, and the light emitting device can be applied to various kinds of light emitting devices such as an organic light emitting device.

1 is a view showing a light emitting device 10 according to an embodiment of the present invention. The light emitting device 10 includes a first electrode 110, a hole injection / transport layer 120, an emissive layer 130, an electron injection layer (EIL) 140, an electron transport layer (ETL) 150, and a second electrode 160.

The first electrode 110 is located on the substrate 100. The first electrode 110 may be provided as an anode. For example, the anode may be provided with ITO (indium tin oxide), which is a transparent electrode having a large work function to facilitate the injection of holes to the HOMO level of the light emitting layer 130. At this time, the ITO electrode can form a pattern through a photo-lithography process.

2 is a view showing a hole injecting / transporting layer 120. FIG. The hole injection / transport layer 120 is located on the first electrode 110. The hole injecting / transporting layer 120 flattens the roughness of the ITO generated through exposure and etching, injects holes from the ITO into the light emitting layer 130, and transfers the holes. The hole injection / transport layer 120 includes graphene or graphene oxide and p-type nickel oxide. For example, as shown in FIG. 2, graphene or graphene oxide may be coordinately bonded to the surface of nickel oxide. Alternatively, for example, the hole injection layer may be formed of PEDOT: PSS (poly (ethylenedioxythiophene): poly-styrenesulphonate)

poly-TPD (poly (N, N'-bis (4-butylphenyl) -N, N'-bis (phenyl) benzidine).

The light emitting layer 130 is located on the hole injection layer 120. The light emitting layer 130 is provided with quantum dots as the light emitting layer 130. The quantum dot is a II-VI compound of CdSe / ZnS, which is a hetero-junction type of a core and shell having a trioctyl phosphine oxide (TOPO) ligand. It has various emission wavelengths depending on the particle size. For example, a white light emitting device including a quantum dot having PL emission characteristics of 530 nm, 620 nm, and 440 nm can be manufactured. Alternatively, the light emitting layer 130 may emit light in any one of red, green, and blue colors.

The electron transporting layer 140 is located on the light emitting layer 130. The electron transport layer 140 transfers electrons injected from the electron injection layer 150 to the light emitting layer 130. The electron transport layer 140 serves as a hole blocking layer for allowing holes injected into the light emitting layer 130 to be well confined in the light emitting layer 130. The electron transport layer 140 may include ZnO nanoparticles which are oxide semiconductors.

The electron injection layer 150 is located on the electron injection layer 150. The electron injection layer 150 injects electrons from the cathode. The electron injection layer 150 may include ZnO nanoparticles which are oxide semiconductors.

The second electrode 160 is located on the electron transport layer 140. The second electrode 160 receives a different voltage from the first electrode 110. The second electrode 160 may be a cathode. As the cathode, a metal electrode having a low work function and excellent in internal reflectivity is used so as to facilitate the injection of electrons to the LUMO level of the light emitting layer 130.

FIG. 3 is a view showing an energy band gap of the light emitting device 10 of FIG. Referring to FIG. 3, the graphene (or graphene oxide) -NiO nanomaterial differs from the HOMO level of the graphene (or graphene oxide) work function of 5.5 eV or less and the NiO nanoparticles of 5.5 eV or more Almost never. Therefore, holes injected from the anode as a single particle can be transferred to NiO nanoparticles. In addition, the HOMO level of 1.8 eV or more of NiO nanoparticles can serve as an electron blocking layer to prevent electrons transferred to the quantum dots from escaping toward the anode. Therefore, the light emitting device 10 can effectively transfer holes in the structure according to the present embodiment.

4 is a view showing synthesis of a graphene quantum dot and a graphene oxide quantum dot. Hereinafter, a process for synthesizing graphene and graphene oxide in the hole injecting / transporting layer 120 will be described. Graphene and graphene oxide are synthesized in a bottom-up fashion. To obtain graphene, first, citric acid is heated to 200 ° C to 500 ° C. At this time, other fine powders including graphite other than citric acid can be used. Thereafter, the heated citric acid is dispersed in the NaOH solvent for the first time. The first time is from 30 minutes to 1 hour and 30 minutes. In one example, the first time may be one hour. The synthesized graphene has blue excitation characteristics. On the other hand, as a method for obtaining graphene oxide, firstly, citric acid is heated to 200 ° C to 500 ° C. At this time, other fine powders including graphite other than citric acid can be used. Thereafter, the heated citric acid is dispersed in a NaOH solvent for a second time. The second time is longer than the first time. And the second time is from 1 hour 30 minutes to 2 hours 30 minutes. As an example, the second time may be two hours. The synthesized graphene has green excitation characteristics. Thereafter, the synthesized graphene or graphene oxide is subjected to centrifugal separation, and finally, the ITO electrode is subjected to O2 plasma treatment to form a film.

NiO is synthesized by sol-gel precipitation method. The synthesized NiO nanoparticles can be graphene or graphene oxide bonded to the NiO surface through thermal reaction or ultrasonic reaction by injecting graphene or graphene oxide dispersed in the aqueous solution. The dispersing property of graphene or graphene oxide can be maintained and dispersed in water or an alcohol-based polar solvent. In addition, when a surfactant such as polyvinylpyrrolidone (PVP) is used in the synthesis or after synthesis of NiO nanoparticles, it is possible to mitigate the decrease in dispersion such as coagulation between nanoparticles in a polar solvent such as water or alcohol. On the other hand, when a surfactant such as propylamine (PA) is used, it can be dispersed in chlorobenzene, dichlorobenzene, chloroform and the like.

The graphene / graphene oxide and NiO nanoparticles can be selected depending on the surface control method. First, NiO nanoparticles or NiP nanoparticles surface-treated with PVP can be easily dispersed in water or alcohol series, and are dispersed in graphene / graphene oxide and a homogeneous solvent to form a single-layered hole injection layer and a hole transport layer Can be formed. On the other hand,

In the case of NiO controlled on the surface of PA or the like, it is possible to disperse NiO in a non-polar solvent such as chlorobenzene, dichlorobenzene or chloroform, and even if the film is formed on the graphene / graphen oxide hole injection layer formed by dispersion in a polar solvent It is possible to deposit in bi-layer form which does not show etching characteristics and hole injection and hole transfer are easy.

5 is a view showing a light emitting device 20 according to another embodiment. The light emitting device 20 of FIG. 5 includes a first electrode 210, a hole injection layer 220, a hole transport layer 230, an emissive layer 240, an electron transport layer (ETL) 250, an electron injection layer (EIL) 260, and a second electrode 270. The first electrode 210, the light emitting layer 240, the electron transport layer 250, the electron injection layer 260, and the second electrode 270 of FIG. 5 are formed on the first electrode 110, the light emitting layer 130, The electron transport layer 140, the electron injection layer 150, and the second electrode 160. The electron injection layer 150 may be formed of a metal such as aluminum, 5 differs from the light emitting device 10 of FIG. 1 in that the hole injecting layer 220 and the hole transporting layer 230 exist independently of each other, in which the hole injecting and transporting are performed in the same layer. The hole injection layer 220 includes graphene or graphen oxide. Graphene or graphene oxide can be produced by the above-mentioned production method. Hereinafter, the overlapping description will be omitted. Further, the hole transport layer 230 includes a p-type nano material. For example, the hole transport layer 230 may include p-type NiO. NiO can be produced by the above-described production method. Hereinafter, the overlapping description will be omitted.

6 is a view showing a process of synthesizing ZnO in the electron transport layer of FIG. 7 is a flowchart according to the synthesis method of FIG. Hereinafter, a process of manufacturing ZnO will be described with reference to FIGS. 6 to 7. FIG.

ZnO nanoparticles can be synthesized by dissolving a zinc compound and a basic substance in an alcohol solvent. At this time, the zinc compound may be a material such as Zn (ClO4) 2 Zn (CH3COO) 2 and Zn (NO3) 2. The basic substance may be provided by KOH, NaOH, LiOH, or the like. The alcohol solvent may be provided in ethanol or methanol. In this embodiment, ZnO nanoparticles are synthesized by sol-gel method. Specifically, (Zn (CH3COO) 2) can be used as a precursor, and KOH can be used as an oxidizing agent.

First, Zn (CH3COO) 2 is dissolved in methanol (S110). Thereafter, the methanol is heated to a first temperature which is a temperature below the boiling point (S120). As an example, the first temperature may be 60 ?. Thereafter, KOH dissolved in methanol is added dropwise to a solution in which Zn (CH3COO) 2 is dissolved (S130). At this time, it can be dropped at a rate of 1 ml / sec. After about 5 minutes, ZnO nuclei are slowly formed. After 60 minutes, about 3 to 5 nm uniform ZnO nanoparticles are synthesized (S140). IPA and hexane are added at a ratio of 1: 1: 5 to remove extra ions such as K + and ZnO nanoparticles synthesized after the reaction, followed by aging for 24 hours (S150, S160). Thereafter, centrifugal separator is used to remove ions and mixed solvents other than the ZnO nanoparticles in the solvent to obtain purified colloidal ZnO nanoparticles (S170). Thereafter, the ZnO nanoparticles are dispersed in ethanol at a constant concentration ratio to obtain purified ZnO nanoparticles (S180).

FIGS. 8 to 11 are views showing the characteristics of the ZnO nanoparticles synthesized by the method of FIG. Figure 8 shows the UV-visible absorption spectrum of the synthesized ZnO nanoparticles. Fig. 9 shows PL characteristics of ZnO. 9 is an XRD result showing the crystal orientation of synthesized ZnO. 10 is a TEM photograph showing a state in which ZnO nanoparticles are relatively uniformly mass-synthesized. Referring to FIG. 7, the maximum absorption wavelength of ZnO is 320.5 nm and has a wide absorption band in the ultraviolet region. In general, PL of ZnO shows a strong peak wavelength in the blue ultraviolet region of 350 nm and a broad wavelength in the visible region of 500 nm. Referring to FIG. 8, it can be seen that the broad wavelength in the 500 nm band is due to oxygen vacancy due to defects of the ZnO nanoparticles, and thus exhibits n-type characteristics. Referring to FIG. 10, the peak wavelength of 2 theta value, which is the same as that of the bulk ZnO crystal, is shown, and it can be confirmed that ZnO having the same composition is synthesized. The results show that the ZnO nanoparticles of hexagonal wurtzite structure have a peak wavelength as shown in FIG. 9 at angles of 31.7 (100), 34.4 (002) and 36.25 (101). Through this, scherre? Calculating the nanocrystal size according to the XRD results in the equation, we can confirm that it is 4.47 nm. Also, referring to FIG. 11, it can be confirmed that the nanoparticles are relatively uniformly mass-synthesized in the form of very small nanoparticles having a size of 3 to 5 nm. The ZnO nanoparticles used as the electron injecting / transporting layer 150 may vary depending on the dispersion concentration of the ZnO nanoparticles in the solvent. As the concentration of dispersed ZnO nanoparticles increases, the characteristics of the device gradually improve, and the characteristics are most excellent at a concentration of 3.0 wt%. At this time, the maximum luminance is 28,760 cd / m < 2 > and the efficiency characteristic is 4.89 cd / A.

FIG. 12 is a view showing the size control and fluorescence characteristics of ZnO nanoparticles according to synthesis conditions. FIG. 13 is a graph showing the characteristics of the ZnO nanoparticles applied to the green quantum dot according to their sizes. In ZnO nanoparticles, the size and shape of the particles can be changed by conditions of related factors such as synthesis time, temperature, and precursor concentration. When ZnO nanoparticles are synthesized by varying the concentration of alcohol solvent and basic substance, Zno nanoparticles with HOMO and LUMO levels can be obtained. Therefore, when ZnO nanoparticles are used as the electron injecting / transporting layer, effective band gap leveling with the light emitting layer 140 having various band gaps depending on the wavelengths is possible. 12 and 13, when the HOMO and LUMO levels are changed according to the sizes of the alcohol solvent and the basic substance, the visible light characteristic of the ZnO nanoparticles changes. Thus, when combined with each R-G-B CdSe / ZnS quantum dot exhibiting other visible light characteristics, the injection of electrons and holes can be leveled as desired.

Further, the light emitting element 10 can be synthesized by interfacial processing of ZnO nanoparticles with a polar or nonpolar surfactant. When a surfactant such as PVP is used to synthesize ZnO nanoparticles, it is possible to mitigate the decrease in dispersion such as aggregation between nanoparticles in a polar solvent such as water or alcohol. On the other hand, when a surfactant such as propylamine (PA) is used to synthesize ZnO nanoparticles, it can be dispersed in chlorobenzene, dichlorobenzene, chloroform, and the like. In addition, the light emitting element 10 can be synthesized by doping ZnO nanoparticles with a metal material. As an example, it can be doped with Al. When ZnO is doped with Al, the lattice constant defects with the Al cathode layer can be minimized as the conductivity increases, so that the probability of injected electrons to be transmitted to the light emitting layer 130 can be increased.

As described above, the light emitting element 10 may be a white light emitting element. Generally, a white color using an organic material has a characteristic that the organic material itself has a broad emission spectrum, and the color rendering index is lowered. However, in the case of quantum dots, the luminescence spectrum is narrower than that of organic materials, and white light having excellent color rendering properties can be realized through combination of quantum dots corresponding to each wavelength.

As described above, the light emitting device according to the present embodiment is a quantum dot light emitting device. However, unlike the above, the light emitting device may be various kinds of light emitting devices. In one example, the light emitting element may be an organic light emitting element. In addition, although the electron injection layer and the electron transport layer are described as being independent in this embodiment, the electron injection layer and the electron transport layer may be provided as a single layer.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, The present invention is not limited to the drawings. In addition, the embodiments described herein are not limited to be applied, and all or some of the embodiments may be selectively combined so that various modifications can be made.

110: first electrode
120: hole injection / transport layer
130: light emitting layer
140: electron transport layer
150: electron injection layer
160: Second electrode
210: first electrode
220: Hole injection layer
230: hole transport layer
240: light emitting layer
250: electron transport layer
260: electron injection layer
270: second electrode

Claims (17)

A first electrode located on the base substrate;
A light emitting layer disposed on the first electrode;
A second electrode located on the light emitting layer;
An electron transport layer positioned between the light emitting layer and the second electrode; And
And a hole injecting / transporting layer positioned between the first electrode and the light emitting layer to inject holes and transfer holes,
Wherein the hole injection / transport layer comprises at least one of graphene and graphene oxide and p-type nickel oxide (NiO)
Wherein the electron transport layer comprises ZnO nanoparticles synthesized by dissolving a zinc compound and a basic substance in an alcohol solvent,
Wherein the HOMO level or the LUMO level is changed according to the concentration of the alcohol solvent and the basic substance when the ZnO nanoparticles are synthesized to control band gap leveling with the light emitting layer. The method according to claim 1,
Wherein the hole injection / transport layer is formed by graphene or graphen oxide coordinated to the surface of nickel oxide (NiO). The method according to claim 1,
The graphene is synthesized by heating citric acid to 200 ° C to 500 ° C, and after the first hour, it is dispersed in NaOH. The method of claim 3,
The graphene oxide is synthesized by heating citric acid to 200 ° C to 500 ° C and adding NaOH after 2 hours to disperse the graphene oxide. 5. The method of claim 4,
Wherein the first time is shorter than the second time. 6. The method of claim 5,
Wherein the first time is from 30 minutes to 1 hour and 30 minutes,
And the second time is from 1 hour 30 minutes to 2 hours 30 minutes. delete delete delete The method according to claim 1,
Wherein the ZnO nanoparticles are surface-treated with a polar or non-polar surfactant. 11. The method of claim 10,
Wherein the ZnO nanoparticles are doped with a metal material. delete delete delete delete delete delete

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