KR20060100151A - Quantom dot light-emitting diode combined with polymer - Google Patents

Abstract

A quantum dot active layer composed of metal or metal oxide nanocrystals spontaneously formed in an insulating polymer without forming holes and electron injection layers of p-type and n-type semiconductor thin films on both sides of the quantum dot active layer or without forming a multilayer conductive polymer that is an electron or hole transport layer. By forming the quantum dot light emitting device can be changed to the size or density of the nanocrystals in the quantum dot active layer without agglomeration of the nanocrystals to obtain a light emitting device having a variety of light emission colors and high luminous efficiency. Since the quantum dot light emitting device uses AC power, low power is consumed and the manufacturing method is simple, thereby reducing cost and effort.

Light Emitting Diode, Quantum Dot, Nano Crystal, Cu2O, Polymer Thin Film

Description

Quantum Dot Light-Emitting Diode Combined With Polymer

1 is a flow chart of a manufacturing method of a quantum dot light emitting device according to the present invention.

2 is an energy band schematic diagram of a quantum dot light emitting device when no voltage is applied.

3 is a schematic diagram of the case in which the AC voltage is applied to the quantum dot light emitting device according to the present invention to excite the electrons in the household appliances.

Figure 4 is a schematic diagram of a process of emitting an photon while the alternating voltage is applied to the quantum dot light emitting device according to the present invention to lose energy.

5 is a schematic view of a quantum dot light emitting device according to the present invention including a quantum dot active layer composed of Cu ₂ O nanocrystals formed in a polyimide.

6 is a planar transmission electron micrograph of a quantum dot active layer composed of Cu ₂ O nanocrystals formed in a polyimide thin film according to the present invention.

7 is an electron diffraction image of Cu ₂ O nanocrystals formed in the polyimide thin film of the quantum dot active layer according to the present invention.

8 is a photoluminescence spectroscopy experiment graph of the quantum dot light emitting device according to the present invention ((1): polyimide thin film formed with Cu2O nanocrystals, (2): polyimide thin film)

The present invention relates to a method for forming a quantum dot active layer for a light emitting device and a light emitting device using the same, and more particularly, to a method for forming a quantum dot active layer for a light emitting device using an inorganic material combined with an organic material and a light emitting device using the same.

Quantum dots are nanoscale semiconductor materials that exhibit quantum confinement effects. When the quantum dot receives light from an excitation source and reaches an energy excited state, the quantum dot emits energy according to a corresponding energy band gap. Therefore, when the size of the quantum dot is adjusted, the corresponding band gap can be adjusted to obtain energy of various wavelength bands.

Quantum dot growth control technology is the most important technology of the future development of semiconductor devices. Metal organic chemical deposition (MOCVD) and molecular beam epitaxy (MBE) are good growth technologies that can control semiconductor thin films at the level of monoatomic layers. However, the quantum dots produced by the gas phase method have good crystallinity, but have a fatal defect in controlling density and uniformity due to lattice mismatch. Thus, it is known that it is difficult to realize a commercially available device using these techniques.

Conventional light emitting devices are manufactured by bonding semiconductor thin films, which are injection layers of p-type and n-type holes and electrons, to both surfaces of a quantum dot light emitting active layer made of GaAs, AlGaAs, etc. (V. Tasco et al. Applied Physics Letters. 84 , 4155-4157 (2004). Recently, however, light emitting devices have been manufactured by inserting inorganic quantum dots such as CdSe into two conductive organic thin film layers (Seth Coe et al. Nature, 420, 800-803 (2002)).

All of the above inventions have the disadvantage of requiring deposition of a multilayer conductive organic layer serving as a semiconductor thin film layer or a charge transfer layer, and in the light emitting device quantum dot structure, a quantum dot structure is formed by a simple method and the density and particle size of the quantum dot The controllable method is not yet disclosed.

Therefore, in the manufacture of a quantum dot structure and a light emitting device using the same, it is possible to form a quantum dot structure by a simple method without such a deposition process, and in particular, a technology capable of controlling the size and density of the nanocrystal particles forming the quantum dots is required. Has been.

The present invention is to solve the above problems, one aspect of the method for forming a quantum dot structure without the deposition process of a semiconductor thin film or multilayer conductive polymer by simply forming an inorganic nanocrystals in the polymer thin film through a simple deposition method and heat treatment will be.

Another aspect of the present invention relates to a quantum dot structure in which inorganic nanocrystals are formed in an insulating polymer thin film.

Still another aspect of the present invention relates to a light emitting device and a method for manufacturing the same, wherein inorganic nanocrystals are formed in an insulating polymer thin film, electrodes are formed at both ends of the insulating polymer thin film, and light is applied by applying an alternating electrode to the formed electrode.

The present invention will be described in more detail below.

The method of forming a quantum dot active layer of the present invention comprises coating a metal on a substrate such as glass or an electrode, dissolving an acidic precursor containing an insulator polymer monomer in a solvent to form a liquid phase, and spin-coating the coated acidic precursor from the coated acid precursor. Removing the solvent, applying heat to the polymeric material such that crosslinking occurs within the coated acid precursor. The density and particle size of the quantum dots formed by changing the type of the metal, the initial deposited thickness of the metal, the mixing ratio of the solvent and the precursor, the conditions of the curing process can be adjusted.

The quantum dot active layer of the present invention comprises a quantum dot composed of metal or metal oxide nanocrystals in the polymer thin film.

The structure of the light emitting device of the present invention is a substrate; A first electrode layer formed on the substrate; A quantum dot active layer made of metal or metal oxide nanocrystals in the polymer thin film formed on the first electrode layer; It is configured to include a second electrode formed on the quantum dot active layer.

The light emitting device operates by using an AC power source and has a relatively low power consumption, unlike a conventional light emitting device that uses a quantum dot in a multilayer conductive organic material and operates by applying a DC power source.

In addition, a flowchart of a method of manufacturing a light emitting device of the present invention is shown in FIG. 1, and the method includes forming a first electrode layer on a front surface of a substrate (S100); Forming a quantum dot active layer made of metal or metal oxide nanocrystals in a polymer thin film on the first electrode layer; And sequentially forming a second electrode layer on the quantum dot active layer (S500).

Preferably, the forming of the quantum dot active layer, coating a metal on the first electrode layer (S200), after dissolving an acidic precursor containing an insulator polymer monomer on the metal layer in a solvent to make a liquid, Spin coating and removing the solvent from the coated acidic precursor (S300), and applying heat to the polymer material (S400) so that crosslinking occurs within the coated acidic precursor.

Preferably, the polymer is polyimide.

The electrodes are preferably conventional electrode materials such as aluminum, copper, and may be indium tin oxide (ITO), indium oxide and other suitable metal oxides, and may be conductive polymers such as PEDOT and doped polyanaline.

The acidic precursor containing the insulator polymer monomer is preferably an acidic precursor containing a carboxyl group.

The method of coating the metal may use known methods such as deposition, sputtering and the like suitable for coating the metal.

The solvent of the present invention may select one or more mixtures selected from N-Metyl-2-Pyrrolidone (NMP), water, N-dimethylacetamide, and diglyme according to the type of insulator precursor. Preferably the solvent is N-Metyl-2-Pyrrolidone (NMP).

Even more preferably, forming the quantum dot active layer comprises: forming an electrode on the substrate; Coating a metal on the electrode; Spin coating polyamic acid of Biphenyltetracaboxylic Dianhydide-p-Phenylenediamine (BPDA-PDA) type using N-Metyl-2-Pyrrolidone (NMP) as a solvent on the coated metal layer and removing the solvent; And heating at about 300 to 400 ° C. for about 1 to 12 hours for curing.

According to the present invention, it is possible to form a quantum dot active layer in which metal or metal oxide nanocrystals dispersed in a polyimide thin film are formed. Since the nanocrystals are uniformly formed in the insulating polymer, the size and density of the nanocrystals can be easily controlled without agglomeration of the crystals, so that the whole device can have a uniform luminous efficiency, and by adjusting the size of the nanocrystals formed therein The emission color can be changed.

Referring to the operation mechanism of the light emitting device according to the present invention.

2 is an energy band schematic diagram of a quantum dot light emitting device when no voltage is applied.

LUMO: lowest energy level with empty electrons in molecular orbits

HOMO: highest energy level filled with electrons in molecular orbits

E _c : the lowest energy level in the conduction band

E _v : highest energy level in valence band

E ₁ : Butid energy level of the quantized ground state formed in the conduction band

HH ₁ : Ground-level boutique energy level of quantized mesoholes formed in valence band

Before applying the voltage, the LUMO level of the insulating polymer and the HOMO level of the insulating polymer and the butyl energy level of the metal or metal oxide nanocrystals in the insulating polymer exist in the neutral state.

3 is a schematic diagram of the case in which the AC voltage is applied to the quantum dot light emitting device according to the present invention to excite the electrons in the household appliances. Since the size of the metal or metal oxide nanocrystals is very small, a very high electric field is formed between the nanocrystals even at a low applied voltage. Therefore, due to the high electric field formed between the nanocrystals, electrons in the valence band valence energy potential (HH ₁ ) in the ground state acquire energy and collide with adjacent electrons. Electrons obtained with great energy by collision at the energy level of the valence band are excited and transitioned to the bounty energy level E ₁ of the conduction band in the ground state.

The electrons excited at the ground state of the conduction band in the bouncy energy level (E ₁ ) lose energy and emit photons having a wavelength corresponding to the transition energy while transitioning to the ground state of the conducting band of the home appliance (HH ₁ ). The light emitting device emits light. 4 is a schematic diagram of a process of emitting photons.

 EXAMPLE

Hereinafter, with reference to the accompanying drawings and embodiments to be described in more detail the present invention. However, the technical idea of the present invention is not limited to the following examples.

Example 1: Fabrication of Light Emitting Diode

An ITO electrode was formed on the glass substrate, and Cu was deposited thereon in a thickness of 1 to 30 nm, followed by precursor Biphenyltetracaboxylic Dianhydide-p-Phenylenediamine (BPDA-PDA) (N-Metyl-2-Pyrrolidone (NMP) as a solvent). Polyamic acid of type PI2610D, DuPont) was spin coated at a volume ratio of 1: 3. Heat was added at 135 ° C. for 30 minutes to evaporate the remaining solvent. Thereafter, heat was applied at 350 ° C. for 4 hours to cure the polyamic acid with polyimide. As a result, nanocrystals uniformly dispersed in the prepared polyimide thin film were formed. An Al electrode was deposited thereon to manufacture a quantum dot light emitting device.

A schematic diagram of the manufactured quantum dot light emitting device is shown in FIG. 5.

Example 2: TEM and Electron Diffraction Analysis

Cu ₂ O nanocrystals in the polyimide thin film prepared above were observed in a JEM 2010 JEOL transmission electron microscope (TEM) and are shown in FIG. 6. According to the planar bright field image of FIG. 6, Cu ₂ O nanocrystals were dispersed in a polyimide thin film, and the size of Cu ₂ O nanocrystals was 5-10 nm or less.

FIG. 7 is a Selected Area Electron Diffraction pattern image of Cu ₂ O nanocrystals formed of nanocrystals in a polyimide thin film. From this, it can be seen that the nanocrystals have a crystal structure and a diffraction ring appears due to the small particle size.

Example 3: Spectroscopic Experiment

Photoluminescence spectroscopy results at 300 ° C. of the light emitting device 1 having the polyimide thin film including Cu ₂ O nanocrystals formed on the glass substrate prepared in Example 1 and the polyimide thin film formed on the glass substrate are shown in FIG. 8. Indicated.

Referring to FIG. 8, the light emitting device according to the present invention has a peak at a wavelength of about 550 nm. On the other hand, the polyimide thin film not containing Cu ₂ O does not have a peak in the visible light region. This is because when the Cu ₂ O nanocrystals are formed in the polyimide, the energy band gap of the Cu ₂ O is smaller than that of the polyimide, so electrons generated by the energy of the laser collect in the Cu ₂ O. Therefore, a peak is observed at a wavelength about the bandgap (2.17 eV) of Cu ₂ O.

The present invention can very simply form a quantum dot active layer for a light emitting device made of metal or metal oxide nanoparticles spontaneously formed in a chemically and electrically stable insulating polymer. In addition, crystals having a uniform distribution as a whole are surrounded by a polymer layer, so that the size and density of nanocrystals can be controlled without agglomeration of crystals, and when used in a light emitting device, various light emission colors and high light emission efficiency can be obtained. Since the quantum dot light emitting device of the present invention uses AC power, low power is consumed and there is no need to form holes and electron injection layers of p-type and n-type semiconductor thin films on both sides of the quantum dot active layer, or to form multilayer organic materials that are electrons or hole transport layers. It is a very useful invention in the field of information and electronic communication because it can reduce the cost and manufacturing time.

Claims (10)

Coating a metal on the substrate; Dissolving an acidic precursor containing an insulator polymer monomer in a solvent to form a liquid phase on the metal layer, followed by spin coating and removing the solvent from the coated acidic precursor; And applying heat to the polymer material to cause crosslinking within the coated acid precursor. The method of claim 1, wherein the polymer is a polyimide. The method of claim 1, wherein the acid precursor containing the insulator polymer monomer is an acid precursor including a carboxyl group. Sputtering Cu on the substrate; Spin-coating Biphenyltetracaboxylic Dianhydide-p-Phenylenediamine (BPDA-PDA) type polyamic acid using N-Metyl-2-Pyrrolidone (NMP) as a solvent on the Cu layer and removing the solvent; And Method of forming a quantum dot active layer comprising heating at about 300 ~ 400 ℃ to cure the polyimide layer. The method of claim 4, wherein the mixing ratio of N-Metyl-2-Pyrrolidone (NMP) and the precursor Biphenyltetracaboxylic Dianhydide-p-Phenylenediamine (BPDA-PDA) is in a volume ratio of 1: 3. A quantum dot active layer comprising quantum dots composed of metal or metal oxide nanocrystals spontaneously formed in an insulating polymer thin film. The quantum dot active layer of claim 6, wherein the insulating polymer is polyimide and the quantum dots are Cu ₂ O nanocrystals.  Board; A first electrode layer formed on the substrate; A quantum dot active layer of claim 6 or 7 formed on the first electrode layer; And a second electrode layer formed on the quantum dot active layer, the quantum dot light emitting device operating using an AC power source.  Forming a first electrode layer on the front surface of the substrate; Forming a quantum dot active layer according to the method of forming a quantum dot active layer of any one of claims 1 to 5 on the first electrode layer; Forming a second electrode layer on the quantum dot active layer manufacturing method of a quantum dot light emitting device.  10. The method of claim 9, wherein the first electrode is ITO and the second electrode is Al.

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