KR100841575B1 - Electroluminescence device and method of fabricating the same - Google Patents

Abstract

A light emitting device and a manufacturing method thereof are provided to use a DC power of relatively low voltage by forming an electron transport layer using a conductive polymer. A first electrode(20) is formed on a substrate(10), and then a quantum active layer(50) is formed on the first electrode. A conductive polymer layer(60) is formed on the quantum active layer, and then a second electrode(70) is formed on the conductive polymer layer. The step of forming the quantum active layer includes spin-coating the first electrode by an acid precursor comprising insulator polymer monomer to form a primary acid precursor layer, forming a metal thin film on the primary acid precursor layer, spin-coating the metal thin film by an acid precursor to form a secondary acid precursor layer, and heating the acid precursor layers.

Description

Light emitting device and method of manufacturing the same {Electroluminescence device and method of fabricating the same}

1 is a schematic view of a light emitting device according to the present invention.

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

3A is a planar bright field image of Cu ₂ O nanoparticles formed between polyimides in a light emitting device manufactured according to the present invention.

3B is a planar bright field image of ZnO nanoparticles formed between polyimides in a light emitting device manufactured according to the present invention.

4 is an energy band diagram in an equilibrium state of the light emitting device of FIG. 1.

FIG. 5 is a device structure diagram of device operation when an electric field is applied outside the light emitting device of FIG. 1.

FIG. 6 is an energy band diagram of device operation when an electric field is applied outside the light emitting device of FIG. 1.

<Explanation of symbols for main parts of the drawings>

10 ... substrate 20 ... first electrode 30 ... polymer thin film

40 ... nanoparticle 50 ... quantum dot active layer 60 ... conductive polymer layer

70 second electrode 100 light emitting element

The present invention relates to a light emitting device using a quantum dot active layer and a method of manufacturing the same, and more particularly, to a light emitting device using metal oxide nanoparticles spontaneously formed in an organic material as a quantum dot active layer and a method of manufacturing 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 (that is, light in the visible light region).

As a light emitting device using conventional nanoparticles as a quantum dot, a light emitting device was manufactured by forming Si nanocrystals in SiO ₂ using a semiconductor material. In this method, Si nanocrystals are formed in an SiO ₂ insulator by ion implantation, and high-voltage electrons are generated across the device to impingement ionization with high-energy electrons. Therefore, the existing semiconductor production process can be used as it is, and due to the characteristics of the material can cause light emission in the Si device difficult to emit light.

However, in the case of a light emitting device using Si nanocrystals embedded in an SiO ₂ insulator, expensive device and process for ion implantation and heat treatment are required for device fabrication, and high efficiency for collision ionization by hot electrons during device operation is required. Voltage is required. In addition, the characteristics of the Si nanoparticles and the SiO ₂ insulating film deteriorate with time due to the high energy electrons generated therein, which causes a problem that the luminous efficiency of the device is lowered. Therefore, when the Si nanocrystals inserted into the existing SiO ₂ insulator are used in the light emitting device, the manufacturing cost is high, the production efficiency is low, and the life of the device is shortened.

As a technology for replacing an existing semiconductor light emitting device, a light emitting device that forms nanoparticles inside a polymer thin film and applies AC power to both ends thereof has been proposed. The device is simple to manufacture, suitable for mass production, and has an advantage of long life and low manufacturing cost by using an insulating polymer that is resistant to external environments.

However, because only the insulating polymer is used to fabricate the device, a relatively high voltage is required to drive the device, and since there is no injection of holes and electrons from the outside, the ion collision must occur by applying an alternating voltage from inside the nanoparticle. However, since the size of the nanoparticles themselves is so small that the electric field actually applied to the nanoparticles is not large compared to the external voltage, the alternating voltage applied across the device must be high for light emission. Therefore, it is impossible to match the device to the current low voltage trend because high voltage AC power must be applied to the device, and it is not compatible with the existing light emitting device driving circuit using the current DC, and high energy holes and electrons due to collision ionization There is a risk of causing degradation of the polymer itself. In addition, the phenomenon that the insulating properties of the insulating polymer due to the applied high voltage is destroyed, there is a possibility that the device itself can no longer be used.

The technical problem to be achieved by the present invention is to provide an organic light emitting device that is driven with high efficiency by a low DC voltage and a method of manufacturing the same.

The light emitting device according to the present invention for achieving the above technical problem, the substrate; A first electrode formed on the substrate; A quantum dot active layer formed on the first electrode and composed of metal oxide nanoparticles in the polymer thin film; A conductive polymer layer formed on the quantum dot active layer; And a second electrode formed on the conductive polymer layer, and is operated using a direct current power source.

Preferably, the polymer thin film is a polyimide thin film, and the metal oxide is selected from the group consisting of zinc oxide, copper oxide, iron oxide, cadmium oxide, cobalt oxide, bismuth oxide, nickel oxide, indium oxide, tin oxide, and combinations thereof. It can be either.

According to another aspect of the present invention, there is provided a light emitting device manufacturing method including: (a) forming a first electrode on a substrate; (b) forming a quantum dot active layer composed of metal oxide nanoparticles in the polymer thin film on the first electrode; (c) forming a conductive polymer layer on the quantum dot active layer; And (d) forming a second electrode on the conductive polymer layer.

In the above method, the step (b) comprises the steps of: preparing a raw material in which the acidic precursor containing the insulator polymer monomer is dissolved in a solvent and spin coating the first electrode to form a primary acidic precursor film; Forming a metal thin film on the primary acidic precursor film; Spin coating the raw material again on the metal thin film to form a secondary acidic precursor film; And applying heat to the primary and secondary acidic precursor films to form the polymer thin film from the curing of the acidic precursor, and simultaneously forming the metal oxide nanoparticles spontaneously formed from the metal thin film.

In step (c), the solvent is removed after forming a MEH-PPV (2,5-bis- (chloromethyl) -1-methoxy-4- (2-ethylhexyloxy) benzene) layer using chloroform as a solvent by spin coating. It may include the step.

The acidic precursor is preferably an acidic precursor containing a carboxyl group. More preferably, in the step (b), the polyamic acid of type Biphenyltetracarboxylic Dianhydride-p-Phenylenediamine (BPDA-PDA) using NMP (N-Methyl-2-Pyrrolidone) as a solvent may be used. Spin coating on the electrode to form a primary polyamic acid film; Forming a Cu or Zn thin film on the primary polyamic acid film; Spin coating the polyamic acid on the Cu or Zn thin film to form a secondary polyamic acid film; And applying heat to the primary and secondary polyamic acid films to form the polymer thin film of polyimide from curing of the polyamic acid and simultaneously form nanoparticles of Cu ₂ O or ZnO spontaneously formed from the Cu or Zn thin film. It includes a step. At this time, it is preferable to apply heat of N ₂ environment, 300-400 ℃ for the curing.

As described above, in the present invention, Cu ₂ O or ZnO nanoparticles may be spontaneously formed in the polyimide thin film by a simple method such as spin coating and heat treatment, and since the conductive polymer layer for electron injection is further present, And holes and electrons are injected into the nanoparticles, respectively, in the second electrode. Therefore, it uses a DC power source, not AC, and emits light through recombination in the nanoparticles even with a low DC voltage without requiring a high voltage as in a conventional device. Therefore, a high voltage for collision ionization is not required, and thus high energy electrons and holes are not generated. Accordingly, a new light emitting device having a long life can be manufactured at low cost without damaging the insulating layer during light emission.

Hereinafter, with reference to the accompanying drawings will be described a preferred embodiment of the method according to the present invention. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various forms, and only the present embodiments are intended to complete the disclosure of the present invention and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you.

(Example)

Light emitting device structure

1 is a schematic view of a light emitting device according to the present invention.

Referring to FIG. 1, the light emitting device 100 according to the present invention includes a substrate 10, a first electrode 20, a quantum dot active layer 50, a conductive polymer layer 60, and a second electrode 70 stacked thereon. It has a structure. Preferably, the structure of the substrate 10 / first electrode 20 / quantum dot active layer 50 / conductive polymer layer / second electrode 70 is spontaneous within the transparent substrate / ITO electrode / polyimide thin film and polyimide thin film The formed Cu ₂ O or ZnO nanoparticles / MEH-PPV (2,5-bis- (chloromethyl) -1-methoxy-4- (2-ethylhexyloxy) benzene) layer / Al electrode have the structure of the light emitting side The substrate 10 is a bottom emission type. However, of course, the light emitting device 100 may have a top-emission structure in which light emission is the second electrode 70.

The thickness of the board | substrate 10 is about 1 mm or less, and a kind is not specifically limited, It is variously possible. For example, the bottom emission type is a transparent substrate as a glass substrate or a plastic substrate. The top emission type is an opaque substrate such as a silicon substrate or a metal foil.

The first electrode 20 formed on the substrate 10 is an electrode (anode) for hole injection, and has a high work function and a transparent metal oxide so that the emitted light can come out of the device in the case of a back emission type. The most widely used material is indium tin oxide (ITO), which may have a thickness of about 50 to 200 nm. While ITO has the advantage of optical transparency, it may not be easy to control. Therefore, in recent years, the use of chemically-doped conjugated polymers, including PT (polythiophene) that has an advantage in the stability to the environment has been considered.

The quantum dot active layer 50 is formed on the first electrode 20 and is composed of metal oxide nanoparticles 40 in the polymer thin film 30. The polymer thin film 30 serves as a hole transporting layer, and may use TPD, a diamine derivative, or poly (9-vinylcarbazole), a photoconductive polymer, but is preferably a polyimide thin film. The nanoparticles 40 serving as the light emitting layer are composed of zinc oxide, copper oxide, iron oxide, cadmium oxide, cobalt oxide, bismuth oxide, nickel oxide, indium oxide, tin oxide, and combinations thereof. It may be any one selected from, and particularly preferably zinc oxide (ZnO) or copper oxide (Cu ₂ O).

As the conductive polymer layer 60 formed on the quantum dot active layer 50, an oxadiazole derivative or the like may be used, and a MEH-PPV layer is particularly preferable. The conductive polymer layer 60 may act as an electron transport layer to more actively inject electrons and use a DC voltage source to increase luminous efficiency.

The second electrode 70 formed on the conductive polymer layer 60 is an electrode (cathode) for electron injection. In case of the bottom emission type, the second electrode 70 is a metal having a small work function of Ca, Mg, and Al. Etc. are used. (On the contrary, in the case of the top emission type, the second electrode 70 is a transparent electrode.) The reason why the metal having the low work function is used as the electron injection electrode is that between the second electrode 70 and the polymer thin film 30. This is because a high current density can be obtained in electron injection by lowering a barrier formed.

In the light emitting device 100, the first electrode 20 injects holes into the nanoparticles 40 through the polymer thin film 30, and the second electrode 70 is formed through the conductive polymer layer 60. By injecting electrons into the nanoparticles 40, electron-holes are paired in the nanoparticles 40, and light is emitted by emitting energy as they recombine.

As such, the combination of the polymer thin film 30-the conductive polymer layer 60 becomes a hole transport layer-the electron transport layer combination to increase the quantum efficiency, and the driving voltage can be lowered through the two-step injection process through the transport layer without the carriers being directly injected. have. In addition, when the electrons and holes injected into the nanoparticles 40 are moved to the opposite electrode through the nanoparticles 40, the recombination is controlled by blocking the opposite transport layer. Through this, the luminous efficiency can be improved.

Conventional devices using Si nanoparticles generate high energy electrons generated by applying a high electric field between SiO ₂ insulating films to emit light, and trap the electrons on Si nanoparticles to emit light. In addition, in the case of a device using only a single insulating polymer, there is no inflow of electrons and holes from the outside, and only electrons and holes can be formed through collision ionization inside the device. . Since these devices do not have a separate layer for injecting or transporting electrons and holes, electrons for light emission have to be dependent on an external electric field caused by high DC and AC voltages. However, the light emitting device of the present invention can emit light even at low voltage because the electrons and holes are directly injected from the outside, and no AC voltage is required.

Light emitting device manufacturing method

Next, a method of manufacturing a light emitting device according to the present invention will be described in detail with reference to FIG. 2.

(Step S1) The first electrode 20 is formed on the substrate 10. For example, a ITO electrode is deposited using a sputtering process.

(Step S2) The quantum dot active layer 50 is formed on the first electrode 10. The quantum dot active layer 50 is composed of the metal oxide nanoparticles 40 in the polymer thin film 30.

Specifically, the quantum dot active layer 50 may be formed by the following steps.

First, a raw material in which an acidic precursor containing an insulator polymer monomer is dissolved in a solvent is prepared, and a primary acidic precursor film is formed by spin coating on the first electrode 20 (step S2-1). The solvent may be selected from any one of NMP (N-Methyl-2-Pyrrolidone), water, N-dimethylacetamide, and diglyme according to the kind of precursor.

Preferably, the acidic precursor uses an acidic precursor containing a carboxyl group. More preferably, the acidic precursor uses a polyamic acid of Biphenyltetracarboxylic Dianhydride-p-Phenylenediamine (BPDA-PDA) type using NMP (N-Methyl-2-Pyrrolidone) as a solvent. By controlling the concentration of the solvent, the rotation speed (rpm) and the rotation time of the spin coating, the thickness of the deposited primary acidic precursor film can be controlled, for example, about 50 nm.

After spin coating, heat may be applied to remove the solvent from the coated primary acidic precursor film. For example, when NMP and polyamic acid are used, heat is applied at 135 ° C. for 30 minutes to remove NMP as a solvent.

Then, a metal thin film is formed on the primary acidic precursor film (step S2-2). The metal may be any one selected from the group consisting of zinc, copper, iron, cadmium, cobalt, bismuth, nickel, indium, tin, and alloys thereof. Preferably, copper (Cu) or zinc (Zn) is deposited to form a thin film. The thickness of the metal thin film can be about 5 nm. The deposition method differs depending on the metal to be deposited, Cu uses thermal evaporation, and Zn uses a sputtering process.

Next, a secondary acidic precursor film is formed by applying the same method as that of forming the primary acidic precursor film on the metal thin film (step S2-3). For example, if the primary acidic precursor film is formed using NMP and polyamic acid, the secondary acidic precursor film is formed again using NMP and polyamic acid, and heat is removed to remove the solvent. In this process, the metal thin film is dissolved in an acidic precursor film to have an ionic form.

Then, the quantum dot active layer 50 is formed by applying heat to the primary and secondary acidic precursor films to form the polymer thin film 30 from the curing of the acidic precursor, and simultaneously forming the metal oxide nanoparticles 40 spontaneously formed from the metal thin film. Is completed (step S2-4).

Here, the step of storing a predetermined time at room temperature before applying heat to the primary and secondary acidic precursor film. In the curing process, the metal ions take oxygen into the metal oxide nanoparticles. Through such a curing action, the present invention can easily form a high density metal oxide nanoparticles 40 uniformly dispersed in the polymer thin film 30.

If NMP and polyamic acid were used, the polymer thin film 30 made of polyimide is formed from curing of the polyamic acid. If Cu or Zn is used as the metal, nanoparticles 40 of Cu ₂ O or ZnO are formed. For curing at this time, heat is applied for 2 hours in an N ₂ environment, 300-400 ° C., more preferably 350 ° C.

Since the nanoparticles 40 formed as described above can be controlled in size and density according to formation conditions, the emission region can be controlled and the emission efficiency can be improved by adjusting the charge trapping and recombination rate according to the applied voltage.

(Step S3) The conductive polymer layer 60 is formed on the quantum dot active layer 50 formed by the above method. Preferably, MEH-PPV using chloroform as a solvent is spin coated to form a layer, and then heat is applied at 135 ° C. for 30 minutes to remove the solvent. Spin coating for 30 seconds at 1200 rpm results in a MEH-PPV layer having a thickness of 70 nm.

(Step S4) The second electrode 70 is formed on the conductive polymer layer 60. For example, Al is formed by vapor deposition.

As described above, according to the light emitting device manufacturing method according to the present invention, the quantum dot active layer 50 made of metal oxide nanoparticles 40 spontaneously formed in the chemically and electrically stable insulating polymer thin film 30 can be formed very simply. . In addition, since the nanoparticles 40 having a uniform distribution as a whole are surrounded by the polymer thin film 30, the size or density can be controlled without agglomeration between the particles, thereby obtaining various emission colors and high luminous efficiency. In particular, the size and density of the nanoparticles 40 may be changed by controlling the heat treatment time for curing and the mixing ratio of the solvent and the acidic precursor, and thus the number and recombination rate of electrons and holes that are captured and recombined by the nanoparticles may be changed. By optimizing for each device, it is easy to control the light emission intensity of the device.

Experimental Example

After the ITO electrode was deposited on the transparent substrate according to the above-described manufacturing method, a polyamic acid film was formed to a thickness of about 50 nm by spin coating a BPDA-PDA type polyamic acid using NMP as a solvent. Then, heat was applied at 135 ° C. for 30 minutes to remove NMP as a solvent. About 5 nm of Cu or Zn was deposited on the coated polyamic acid film. Then, the polyamic acid was spin-coated again to further form a polyamic acid film having a thickness of about 50 nm. Heat was also applied at 135 ° C. for 30 minutes to remove NMP as a solvent. After storage at room temperature for 24 hours, heat was applied for 2 hours at 350 ° C. in an N ₂ environment to cure the polyamic acid to obtain a polyimide, and at the same time, nanoparticles of Cu ₂ O or ZnO were formed.

Figure 3a is a scanning electron microscope (TEM) of the Cu ₂ O nanoparticles in the polyimide thin film prepared by the above method, a planar bright field image, Figure 3b is a polyimide thin film prepared by the method Plane bright field image of ZnO nanoparticles.

3A and 3B, it can be confirmed that the Cu ₂ O or ZnO nanoparticles are very evenly formed in the polyimide thin film, and the size of each nanoparticle is 5-10 nm or less.

Operating principle of light emitting device

The operation mechanism of the light emitting device according to the present invention will be described with reference to the energy band diagram.

FIG. 4 is an energy band diagram of the light emitting device 100 of FIG. 1, that is, a state in which no voltage is applied. here,

E _c : lowest energy level in the conduction band of the nanoparticles 40,

E _v : the highest energy level in the valence band of the nanoparticle 40,

E _LUMO : lowest energy level with empty electrons in the polymer thin film 30,

E _HOMO : the highest energy level filled with electrons in the polymer thin film 30,

E _F : Fermi level of each electrode 20, 70.

Referring to FIG. 4, holes are injected by the first electrode 20 and electrons are injected by the second electrode 70 into the device. Since ITO, which is a preferred material of the first electrode 20, and polyimide, which is a preferred material of the polymer thin film 30, have a lower energy barrier to holes, holes may be removed from the first electrode 20 to the polymer thin film 30. Injected, the polymer thin film 30 serves as a hole transport layer. On the contrary, Al, which is a preferred material of the second electrode 70, and MEH-PPV, which is a preferred material of the conductive polymer layer 60, have a conductive polymer layer (at the second electrode 70) because the energy barrier to electrons is lower than that of holes. 60, electrons are injected, and the conductive polymer layer 60 serves as an electron transport layer.

FIG. 5 is a device structure diagram of device operation when an electric field is applied outside the light emitting device 100 of FIG. 1.

As shown in FIG. 5, a positive voltage is applied to the first electrode 20 and a negative voltage is applied to the second electrode 70. Holes injected from the first electrode 20 pass through the polymer thin film 30 and are trapped by the nanoparticles 40 formed in the polymer thin film 30. Electrons injected from the second electrode 70 are injected into the polymer thin film 30 through the conductive polymer layer 60. Since the difference in the energy barrier of the electrons of the conductive polymer layer 60 and the polymer thin film 30 is lower than that of the second electrode 70 and the polymer thin film 30, the electrons are easily injected into the polymer thin film 30 and thus the nanoparticles. Captured at 40.

6 is an energy band diagram for device operation when a voltage is thus applied.

Referring to FIG. 6, electrons and holes injected from both electrodes 20 and 70 are trapped in the nanoparticles 40, respectively, and undergo electron-hole recombination therein. The generated light is emitted to the outside through the first electrode 20 and the substrate 10, as indicated in FIG. 5. The emitted light has a wavelength corresponding to the energy of the forbidden band of the nanoparticles 40 formed in the polymer thin film 30.

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

As described above, the present invention proposes a high-efficiency light emitting device composed of nanoparticles formed spontaneously in a conductive polymer layer serving as an electron transporting layer and a polymer thin film serving as a light emitting layer, and a method of manufacturing the same.

The light emitting device according to the present invention forms a separate electron transport layer using a conductive polymer to emit light in a structure using only a single layer insulating polymer and a light emitting device using Si nanoparticles formed in a conventional SiO ₂ thin film requiring a high DC voltage. Unlike light emitting devices that require a high alternating current voltage to be applied, electrons and holes are injected directly from both electrodes, so a relatively low voltage DC power supply can be used.

In addition, since there is no collision ionization by high energy electrons in the existing devices, there is no deterioration of the device characteristics, thereby extending the life of the device. It is possible to optimize accordingly. Therefore, a high efficiency, long life and low power consumption light emitting device can be obtained without deteriorating the characteristics of the insulating film over time of use.

According to the production method according to the present invention, it is possible to very easily form a quantum dot active layer made of metal oxide nanoparticles spontaneously formed in a chemically and electrically stable insulating polymer thin film. In addition, nanoparticles having a uniform distribution as a whole are surrounded by a polymer thin film so that the size and density of nanoparticles can be controlled without agglomeration of crystals and various light emission colors and high luminous efficiency can be obtained by using them in light emitting devices. Therefore, the high efficiency OLED and the image display device using the same can be used in the liquid crystal screen replacement of a mobile phone, a large image display device including a monitor, a television, an electronic display, and an illumination device.

The size and density of the metal oxide nanoparticles spontaneously formed in the polymer thin film can be changed by controlling the heat treatment time, the mixing ratio with the solvent and the precursor. By optimizing for the compound semiconductor, it is easy to control the light emission intensity of the light emitting device.

Claims (11)

delete delete delete delete (a) forming a first electrode on the substrate; (b) forming a quantum dot active layer composed of metal oxide nanoparticles in the polymer thin film on the first electrode; (c) forming a conductive polymer layer on the quantum dot active layer; And (d) forming a second electrode on the conductive polymer layer, In step (b), Preparing a raw material in which an acidic precursor including an insulator polymer monomer is dissolved in a solvent and spin coating the first electrode to form a primary acidic precursor film; Forming a metal thin film on the primary acidic precursor film; Spin coating the raw material again on the metal thin film to form a secondary acidic precursor film; And And applying heat to the primary and secondary acidic precursor films to form the polymer thin film from curing of the acidic precursor and simultaneously forming the metal oxide nanoparticles spontaneously formed from the metal thin film. Manufacturing method. The method of claim 5, wherein the polymer thin film is a polyimide thin film. The method of claim 5, wherein the metal is any one selected from the group consisting of zinc, copper, iron, cadmium, cobalt, bismuth, nickel, indium, tin, and alloys thereof. The method of claim 5, wherein the acidic precursor is an acidic precursor containing a carboxyl group. (a) forming a first electrode on the substrate; (b) forming a quantum dot active layer composed of metal oxide nanoparticles in the polymer thin film on the first electrode; (c) forming a conductive polymer layer on the quantum dot active layer; And (d) forming a second electrode on the conductive polymer layer, In step (b), Biphenyltetracarboxylic Dianhydride-p-Phenylenediamine (BPDA-PDA) type polyamic acid using NMP (N-Methyl-2-Pyrrolidone) as a solvent is spin coated on the first electrode to form a primary polyamic acid film. Doing; Forming a Cu or Zn thin film on the primary polyamic acid film; Spin coating the polyamic acid on the Cu or Zn thin film to form a secondary polyamic acid film; And Applying heat to the primary and secondary polyamic acid films to form the polymer thin film of polyimide from curing of the polyamic acid and simultaneously form nanoparticles of Cu ₂ O or ZnO spontaneously formed from the Cu or Zn thin film Light emitting device manufacturing method comprising a. The method of claim 9, wherein the N ₂ environment, 300-400 ℃ heat is applied to the curing method. The method of claim 5 or 9, wherein the step (c) is a MEH-PPV (2,5-bis- (chloromethyl) -1-methoxy-4- (2-ethylhexyloxy) benzene) layer using chloroform as a solvent. Forming a spin coating to form a light emitting device comprising the step of removing the solvent.

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