KR20220102370A - Simplified multi-layer thin film formation method and display device manufactured using the same - Google Patents

Abstract

The present invention relates to a simplified multilayer membrane formation method and a display element manufactured by using the same. Provided are the multiplayer membrane formation method using only wet methods through the process of coating a solution in which a ligand is attached, and the polymer is dissolved on the substrate, and the display element manufactured by using the same.

Description

Simplified multilayer thin film formation method and display device manufactured using the same

The present invention relates to a method for forming a multilayer thin film and a display device manufactured using the same, and more particularly, a method for forming a multilayer thin film and using the same, which is simplified by coating a solution in which a polymer and a quantum dot to which a ligand is attached are dissolved on a substrate It relates to a display device manufactured by

Display technology is largely divided into quantum dot light emitting diode technology using quantum dots composed of inorganic materials and organic light emitting diode technology using organic compound film.

A quantum dot (QD) is a nanometer-sized semiconductor particle. In this case, if the size is smaller than Bohr's exciton radius, the movement of electrons is restricted and the energy level has a discontinuous value, which is called the quantum confinement effect. Quantum dots are used in various optoelectronic devices, such as light emitting diodes (LEDs), optical sensors, and solar cells, because their electrical and optical properties vary according to their size, shape, and composition due to the quantum confinement effect. In particular, since the emission wavelength can be controlled according to the size and color purity and color reproducibility are excellent due to a narrow half-width, it is widely used in display devices. A TV under the brand name of QLED, which has recently been successfully commercialized, has greatly improved color reproducibility, which is a disadvantage of LCD, by replacing the fluorescent material in the LED of the LCD backplane with quantum dots. This utilizes the photo-luminescence (PL) characteristics of quantum dots, and recently, research on electro-luminescence (EL) type devices (QD-LEDs) using quantum dots itself as a light emitting layer has been actively conducted. Is in progress.

In order to manufacture high-efficiency QD-LEDs, it is very important to synthesize quantum dots with high quantum efficiency. In QD-LEDs, a quantum dot consists of a core and a shell, and the core is a part where actual light emission occurs, and the size of the core determines the emission wavelength. The shell encloses the core, prevents oxidation of the core, and improves the stability and quantum efficiency of quantum dots by reducing traps on the surface of the core. Therefore, in order to improve the quantum efficiency of quantum dots, many attempts have been made to control the thickness or composition of the shell, and to facilitate injection or extraction of electrons and holes, a quantum dot of a rod structure in which different shells are heterojunctioned around a core. Various methods have been reported, such as introducing Group II-VI quantum dots, represented by Cd and Se, currently exhibit excellent performance with quantum efficiency approaching 100%, and recently, group III-V quantum dots such as InP are being actively developed to replace Cd, a heavy metal.

However, perovskite, group II-VI, and group III-V quantum dots currently used as quantum dots have a problem in that the quantum dots are dissolved in the solvent because the quantum dots do not have resistance to solvents during the process. Therefore, there was a big problem in stacking quantum dots of various sizes that emit red, green, and blue light on a substrate in a display device process. In particular, in the case of perovskite quantum dots, there was no option for a solvent in which the quantum dots were not dissolved because the characteristics of the perovskite having strong polar bonding and the characteristics of the quantum dots having a strong non-polar ligand were coexisted. Therefore, in the conventional display device process, most of the process was to form all the functional layers after the perovskite quantum dots through evaporation in a vacuum. That is, in the prior art, the polar solvent quenches the perovskite itself and causes damage, and the non-polar solvent dissolves the perovskite quantum dots. This necessary disadvantage existed.

It is an object of the present invention to provide a method of forming a multilayer thin film including quantum dots of uniform size in one step, which does not require an evaporation method in a high vacuum state.

Another object of the present invention is to provide a display device manufactured using the method for forming a multilayer thin film.

In order to solve the above problem, the method for forming a multilayer thin film according to an embodiment of the present invention comprises the steps of: a) dissolving a ligand-attached quantum dot and a polymer in an organic solvent: and b) dissolving the quantum dot and the polymer into a substrate Including the step of coating on the top, the phase separation occurs on the substrate during the coating process of step b).

In this case, the polymer may act as a hole transport layer as a conductive polymer.

In addition, the quantum dots may include perovskite quantum dots.

The coating in step b) may be specifically spin coating. And the polymer may form a network through the spin coating. The quantum dots may be filtered by the formed polymer network and phase separation may occur.

More specifically, the method for forming a multilayer thin film according to an embodiment of the present invention includes, after step b), c) removing the quantum dots on the phase-separated coating layer by using a selective solvent on the substrate on which the coating layer is formed. More specifically, step c) may be a step of dissolving quantum dots that have not passed through the polymer network formed in the coating layer with a selective solvent, thereby removing the quantum dots on the phase-separated coating layer.

In this case, the quantum dots may be perovskite quantum dots, and the optional solvent may be octane.

A display device according to another embodiment of the present invention is manufactured using one of the above multilayer thin film forming methods.

Conventional QD-LEDs devices have a disadvantage in that the process time is long by using a dry method to deposit an electron transport layer or a hole transport layer after depositing the quantum dot emission layer, but according to an embodiment of the present invention, the quantum dot emission layer and the The electron transport layer can be wet deposited in one go. Therefore, in the process of manufacturing the display device, there is an effect that the process time is greatly shortened by using only the wet method without the need for a dry method requiring a high vacuum state.

1 is a conceptual diagram showing the state of a solution in which a quantum dot to which a ligand is attached and a polymer are dissolved together in an organic solvent according to an embodiment of the present invention.
2 is a conceptual diagram illustrating a phase-separated state after spin-coating the solution of FIG. 1 on a substrate according to an embodiment of the present invention.
3 is a conceptual diagram illustrating a state in which the quantum dots on the coating layer are removed using a selective solvent for the coating of FIG. 2 according to an embodiment of the present invention.
4 is a comparison of luminescence data before and after dissolving the upper portion of the coating layer with a selective solvent.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Prior to this, the terms or words used in the present specification and claims should not be construed as being limited to conventional or dictionary meanings, and the inventor should properly understand the concept of the term in order to best describe his invention. Based on the principle that it can be defined, it should be interpreted as meaning and concept consistent with the technical idea of the present invention.

Therefore, the embodiments described in this specification and the configurations shown in the drawings are only the most preferred embodiment of the present invention, and do not represent all of the technical spirit of the present invention, so at the time of the present application, they can be replaced It should be understood that various equivalents and modifications may be made.

A method of forming a multilayer thin film according to an embodiment of the present invention is as follows. First, the quantum dots to which the ligand is attached and the polymer are dissolved together in an organic solvent. 1 is a conceptual diagram schematically illustrating a state in which a polymer 14 and a quantum dot 13 to which a ligand 12 is attached are dissolved in an organic solvent 11 . The multilayer thin film may be specifically a quantum dot-based display device.

In the multilayer thin film forming method, the polymer may act as a hole transport layer, and the polymer is preferably a conductive polymer material to act as a hole transport layer. Specifically, it is preferable that the conductive polymer materials have a band gap suitable for transporting holes to be used as the hole transport layer.

Conductive polymers having a bandgap suitable for transporting the holes are, for example, PVK (poly(vinyl carbazole)), TFB (thieno[2,3-f]benzofuran), Poly-TPD ( Poly(N,N'-bis-4-butylphenyl-N,N'-bisphenyl)benzidine) may be used, but is not limited thereto. In an example of the present invention, an experiment was conducted using the TFB polymer.

The quantum dot may be a group II-VI quantum dot or a group III-V quantum dot, but preferably a quantum dot composed of perovskite may be used. Quantum dots have different wavelengths of light emitted according to their size, and quantum dots that preferably emit red (R), green (G), and blue (B) respectively are required for use in a display device. The larger the size of the quantum dot, the longer wavelength light is emitted, and preferably, in order to emit visible light, the quantum dot having a diameter of 5 nm to 50 nm may be suitable for use in a display device.

As the ligand, a ligand attached to quantum dots may be used, and specifically, 1-dodecanethiol, 3-mercaptopropionic acid, trioctylphosphine, and trioctyl. Primary amines such as trioctylphosphine oxide, oleic acid, and oleylamine may be exemplified, but the examples are not limited thereto.

As the organic solvent for dissolving the polymer and quantum dots, general organic solvents may be used, and specifically, chloroform, toluene, octane, heptane, hexane, pentane, tetrahydrofuran, chlorobenzene, and the like may be exemplified. Preferably, however, the solvent may be toluene.

The solution in which the polymer and quantum dots are dissolved is coated on a flat substrate, preferably by spin coating. The spin coating method is a method of spreading the fluid widely by centrifugal force while placing the fluid on the substrate and rotating it at high speed in order to produce a thin and uniform layer. The spin coating method proceeds through three major processes (material application, rotation, and curing). Preferably, the rotation speed per minute of the spin coating may be 1500 to 5000 RPM, the combined concentration of the quantum dots and the polymer in the solution may be 10 to 100 mg/ml, and the rotation time may be 30 to 60 seconds.

The substrate may preferably be a substrate on which an electron transport layer is deposited on top. Therefore, the method of forming a multilayer thin film according to an embodiment of the present invention can be viewed as a method of depositing quantum dots and a hole transport layer on the electron transport layer at the same time.

The polymer dissolved in the solution during the spin coating process forms a network during the curing process. However, in the spin coating process, the formation of the polymer network occurs earlier than the curing rate of the entire solution. At this time, the perovskite quantum dots try to precipitate under the solution due to their high density, but due to the polymer network formed first during the spin coating process, only uniform and small quantum dots that can pass through the polymer network can be precipitated under the solution. have. Among the quantum dots, the quantum dots that do not pass through the polymer network due to their size cannot be precipitated in solution, and spin coating can be finished while remaining on the polymer network.

When the spin coating is finished, small, relatively small and uniform quantum dots are located at the bottom, and then the polymer network and the relatively large and non-uniform quantum dots that do not pass through the polymer network are in a state of phase separation.

2 is a conceptual diagram schematically illustrating a state in which the solution is phase-separated and coated through the spin coating process, in a relatively small and uniform shape passing through the polymer network based on the polymer network 23 on the upper portion of the substrate 21. The quantum dot light emitting layer 22 including quantum dots and the polymer network cannot be communicated and are divided into a layer 24 including quantum dots having a relatively large and non-uniform shape. Specifically, the quantum dot size of the quantum dot light emitting layer 22 deposited under the polymer network may be 20 nm or less, and may be a quantum dot emitting visible light.

After the coating process, it is possible to wash out only the quantum dots on the upper part of the polymer network by using a selective solvent that dissolves only quantum dots, preferably perovskite quantum dots, without dissolving the polymer network on the upper part of the coating layer. The solvent may preferably be octane, but is not limited thereto.

3 is a schematic diagram showing a state in which the layer 24 including relatively large and non-uniform quantum dots on the upper polymer network is washed out using the selective solvent.

4 is data comparing the amount of light by quantum dots according to the wavelength of the multilayer thin film (Pristine) on which the spin coating is finished according to an embodiment of the present invention and the multilayer thin film (Cleaned) after dissolving the upper portion of the coating layer with octane to be. Referring to FIG. 4 , the amount of light of the multilayer thin film (Cleaned) in which the upper part of the coating layer is dissolved with octane is higher in the visible ray region than before (Pristine) when the upper part of the coating layer is dissolved (Pristine). This can be seen as the effect that the light emitted from the quantum dots of uniform size under the electron transport layer contributing to light emission can more efficiently emit light to the outside as the non-uniformly sized quantum dots on the electron transport layer disappear. .

A display device according to another embodiment of the present invention is a multilayer thin film display device manufactured using the method for forming a multilayer thin film. Specifically, the display device may be a TV, a mobile phone, or a watch device, but is limited to the above example. doesn't happen

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and variations are possible within the scope without departing from the technical spirit of the present invention described in the claims. It will be apparent to those of ordinary skill in the art.

11: organic solvent
12: ligand
13: quantum dots
14: polymer
21: substrate
22: quantum dot light emitting layer comprising quantum dots of a relatively small and uniform shape
23: polymer network
24: A layer containing relatively large and non-uniformly shaped quantum dots

Claims (10)

a) dissolving the ligand-attached quantum dots and polymer in an organic solvent: and
b) coating a solution in which the quantum dots and the polymer are dissolved on the substrate;
A method of forming a multilayer thin film, characterized in that phase separation occurs on the upper portion of the substrate in the coating process of step b).
According to claim 1,
The polymer is a conductive polymer and a method for forming a multilayer thin film, characterized in that it acts as a hole transport layer.
According to claim 1,
The quantum dot is a multilayer thin film forming method comprising perovskite quantum dots.
According to claim 1,
The coating of step b) is a method of forming a multilayer thin film, characterized in that spin coating.
5. The method of claim 4,
A method for forming a multilayer thin film, characterized in that the polymer forms a network through the spin coating.
6. The method of claim 5,
The quantum dots are filtered by the polymer network and a multilayer thin film forming method, characterized in that the phase separation occurs.
According to claim 1,
After step b),
c) using a selective solvent on the substrate on which the coating layer is formed, removing the quantum dots on the upper portion of the phase-separated coating layer;
8. The method of claim 7,
The step c) is a step of dissolving the quantum dots that have not passed through the polymer network formed in the coating layer with a selective solvent to remove the quantum dots on the upper portion of the phase-separated coating layer;
8. The method of claim 7,
The quantum dots are perovskite quantum dots,
The selective solvent is a method of forming a multilayer thin film, characterized in that octane.
A display device manufactured using any one of the methods of claims 1 to 9.

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