KR100848151B1 - Organic light emitting diode display panel and method for preparing the same - Google Patents

Abstract

The present invention relates to an organic light emitting display panel and a method of manufacturing the same, and more particularly, to an anode formed on a substrate; An organic film formed on the anode; And a cathode formed on the organic layer, wherein the organic layer includes a buffer layer, a hole transport layer, and a light emitting layer sequentially stacked from the bottom, wherein the hole transport layer comprises MEH-PPV and MEH-PPV. The present invention relates to an organic light emitting display panel comprising 0.2 to 0.5% by weight of single-walled carbon nanotubes.

The organic light emitting display panel according to the present invention has an advantage of excellent device performance due to high current density and low turn-on voltage because of excellent hole mobility.

OLED display, MEH-PPV, single-walled carbon nanotubes

Description

Organic light emitting display panel and method for manufacturing same

1 is a cross-sectional view illustrating a part of an organic light emitting display panel according to an exemplary embodiment of the present invention.

2 is a schematic diagram of an energy level of an organic light emitting display panel according to another exemplary embodiment of the present invention.

3 is a result of measuring the current voltage characteristics of the device to move only the holes manufactured according to Examples 1 and 2 and Comparative Examples 1 and 2.

4 is a graph measuring values for PL and EL of the organic light emitting display panels manufactured in Examples 3 and 5. FIG.

5A and 5B are graphs measuring values for current, voltage, light intensity, and efficiency of organic light emitting display panels manufactured according to Examples 5 and 6 and Comparative Examples 3 and 4;

<Description of Drawing Major Symbols>

100: substrate 131: anode

132: organic film 133: cathode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic light emitting display panel and a method of manufacturing the same. More particularly, the present invention relates to an organic light emitting display panel and a method of manufacturing the same, having high current density and low turn-on voltage due to excellent hole mobility. .

In general, a flat panel display panel is a device having a flat surface using visible light, and when a strong voltage is applied between two electrodes, gas (Gas) discharge is generated between the electrodes. PDP (Plasma Display Panel) using the light emitting phenomenon, electrons emitted from a flat cathode (Cathode) is applied to the FED (electroluminescent display), the filament (Filament) that hits the phosphor and emits heat electrons In this case, electrons are accelerated in the grid to reach the anode, and a current flows through a thin film of VFD (fluorescent fluorescent display), fluorescent or phosphorescent organic material, which displays information by hitting and emitting a patterned phosphor to emit light. OLED (organic light emitting display panel), a self-luminous type in which light is generated when the main surface electrons and holes combine in an organic material layer Display that applies the electrical property of liquid crystal, which is the intermediate state between liquid and solid, to a display device, and displays information using the principle that liquid crystal acts as a shutter and transmits or blocks light according to voltage switching. There is an LCD (Liquid Crystal Display). In particular, organic light emitting display panels (OLEDs) have been attracting attention as next-generation display devices because of their advantages such as wide viewing angle, excellent contrast, and fast response speed.

An organic light emitting display panel is formed by forming an anode (anode) on a glass or other substrate, forming an organic film on the anode, and sequentially stacking a cathode (cathode) thereon. In this case, the organic layer has a structure in which the hole transport layer, the light emitting layer, and the electron transport layer are sequentially or selectively stacked in a stacked manner. As the anode, a transparent electrode such as ITO is used, and as a cathode, a metal having a low work function (Ca, Li, Al: Li, Mg: Ag, etc.) is used, and an organic layer is laminated between the anode and the cathode. do.

When a forward voltage is applied to these panels, holes and electrons are injected from the anode and the cathode, respectively, and the injected holes and electrons combine to form excitons, and excitons are radiative recombination. To cause an electroluminescence phenomenon.

However, the conventional organic light emitting display panel has a problem in that current mobility is low due to poor mobility of holes, and the turn-on voltage is not sufficiently low.

Accordingly, an object of the present invention is to provide an organic light emitting display panel with increased hole mobility and low turn-on voltage.

Another object of the present invention is to provide a method of manufacturing the organic light emitting display panel.

The present invention to achieve the first technical problem,

An anode formed on the substrate; An organic film formed on the anode; And a cathode formed on an upper portion of the organic layer.

The organic layer includes a buffer layer, a hole transport layer, and a light emitting layer sequentially stacked from the bottom,

The hole transport layer includes an organic light emitting display panel including MEH-PPV and 0.2 to 0.5 wt% single-walled carbon nanotubes based on the MEH-PPV.

According to a preferred embodiment of the present invention, the cathode may be made of gold (Au).

According to another preferred embodiment of the present invention, the buffer layer may be a PEDOT: PSS layer.

According to another preferred embodiment of the present invention, the thickness of the hole transport layer may be 400 to 600 kPa.

According to another preferred embodiment of the present invention, an electron transport layer including tris (8-hydroxyquinoline) aluminum (Alq ₃ ) may be further included on the hole transport layer.

According to another preferred embodiment of the present invention, the electron transporting layer may further include 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM). Can be.

The present invention to achieve the second technical problem,

(a) forming a buffer layer on the substrate;

(b) forming a hole transporting layer by laminating a nanocomposite comprising MEH-PPV and 0.2-0.5% by weight single-wall carbon nanotubes based on the MEH-PPV on top of the buffer layer; And

(c) a method of manufacturing an organic light emitting display panel comprising forming a cathode on the hole transport layer.

According to a preferred embodiment of the present invention, the cathode may be made of gold (Au).

According to another preferred embodiment of the present invention, the buffer layer may be a PEDOT: PSS layer.

According to another preferred embodiment of the present invention, the thickness of the hole transport layer may be 400 to 600 kPa.

According to another preferred embodiment of the present invention, the method may further include forming an electron transport layer including tris (8-hydroxyquinoline) aluminum (Alq ₃ ) on the hole transport layer.

According to another preferred embodiment of the present invention, the electron transporting layer may further include 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM). Can be.

According to another preferred embodiment of the present invention, the step of forming the electron transport layer comprises the step of vaporizing the Alq ₃ by heating the crucible containing the Alq ₃ by applying a voltage; Allowing the Alq ₃ vapor to pass through the nozzle above the crucible to form a cluster; And depositing the Alq ₃ vapor on the hole transport layer to form an electron transport layer.

According to another preferred embodiment of the present invention, the temperature of the crucible may be 250 to 300 ℃.

According to another preferred embodiment of the present invention, the deposition rate may be 1 ~ 2 Å / sec.

Hereinafter, the present invention will be described in more detail.

An organic light emitting display panel according to the present invention includes an anode formed on a substrate; An organic film formed on the anode; And a cathode formed on the organic layer, wherein the organic layer includes a buffer layer, a hole transport layer, and a light emitting layer sequentially stacked from the bottom, wherein the hole transport layer comprises MEH-PPV and MEH-PPV. It is characterized in that it comprises 0.2 to 0.5% by weight single-wall carbon nanotubes as a standard.

1 is a cross-sectional view illustrating a part of an organic light emitting display panel according to an exemplary embodiment of the present invention.

Referring to FIG. 1, an organic light emitting display panel according to an exemplary embodiment of the present invention includes an anode 131 formed on the substrate 100, an organic layer 132 stacked on the anode 131, And a cathode 133 covering the organic layer 132.

The substrate 100 may be made of glass, plastic, or metal, and although not shown in the drawing, the substrate may include a thin film transistor, a capacitor, and the like, and a general pixel circuit may be formed.

In addition, the anode 131 is formed in a pattern corresponding to each pixel on the substrate 100, although not illustrated in FIG. 1, the anode 131 is electrically connected to a pixel circuit provided in the substrate 100. .

An insulating film 120 provided with an insulator is formed to cover the anode 131, and an opening 121 is formed in the insulating film 120 to expose the anode 131.

The organic layer 132 is formed to cover the anode 131 in a shape corresponding to the exposed opening 121 of the insulating layer 120, and a cathode 133 is formed on the organic layer 132. . The cathode 133 may be formed to cover all of the pixels, but is not limited thereto and may be patterned.

In addition, the anode 131 may function as an anode electrode, and the cathode 133 may function as a cathode electrode, and vice versa. In all the following embodiments, the case where the anode 131 functions as an anode electrode has been described as an example, but vice versa.

On the other hand, when the bottom emission type (bottom emission type), the anode 131 may be provided as a transparent electrode, the cathode 133 may be provided as a reflective electrode. At this time, such a transparent electrode can be formed using a high work function and transparent ITO, IZO, In ₂ O ₃ , ZnO, etc., the reflective electrode to be the cathode 133 is Ag, Mg, Al, It may be provided with a metal material such as Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca and compounds thereof.

In addition, in the case of a top emission type, the anode 131 may be provided as a reflective electrode, and the cathode 133 may be provided as a transparent electrode. At this time, the reflective electrode serving as the anode 131 is formed of a reflective film of Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, or a compound thereof, and then a work function thereon. It may be made by forming a high ITO, IZO, ZnO, In ₂ O ₃ or the like. The transparent electrode serving as the cathode 133 is formed by depositing a metal having a small work function, that is, Ag, Mg, Al, Pt, Pd, Au, Ni, Nd, Ir, Cr, Li, Ca, and compounds thereof. Subsequently, an auxiliary electrode layer or a bus electrode line may be formed on the transparent conductive material such as ITO, IZO, ZnO, or In ₂ O ₃ .

In the case of a double-sided light emission type, both the anode 131 and the cathode 133 may be provided as transparent electrodes.

The positive electrode 131 and the negative electrode 133 are not necessarily limited to those formed of the above-described materials, and may be formed of a conductive organic material or a conductive paste containing conductive particles such as Ag, Mg, and Cu. In the case of using such a conductive paste, it may be printed using an inkjet printing method, and after printing, may be baked to form an electrode.

In the organic light emitting display panel according to the present invention, the cathode may be made of a metal having a large work function, and thus, the hole-moving device may be manufactured. The metal having the large work function may be gold (Au), and the work function may be 5.2 eV.

As long as the buffer layer is used as a buffer layer of an organic light emitting display panel, all materials conventional in the art may be used, and for example, the buffer layer is preferably a PEDOT: PSS layer.

The organic light emitting display panel according to the present invention uses a high purity single-walled carbon nanotubes in addition to MEH-PPV (poly (2-methoxy-5- (2-ethylhexyloxy) -1,4-phenylenevinylene)) to improve hole mobility. It is characterized by high current density and low turn-on voltage since the hole injection effect can be improved.

In the nanocomposite of MEH-PPV and single-walled carbon nanotubes, the content of single-walled carbon nanotubes is 0.2 to 0.5% by weight based on the MEH-PPV. When exceeding%, it is not preferable because External Quantum Efficiecy (EQE) tends to decrease.

On the other hand, the hole transport layer preferably has a thickness of 400 to 600 kPa, if less than 400 kPa, the physical stability of the film is lowered, there is a fear of the film forming itself in the actual use environment, if it exceeds 600 kPa, the mobility of the hole may be lowered have.

In addition, the organic light emitting display panel according to the present invention may be manufactured as a heterojunction device by further including an electron transport layer including Alq ₃ on the emission layer, in which case it is not doped by simply using Alq ₃ . The device may be made of an undoped device, or may be manufactured of a doped device by doping Alq ₃ with a dopant. The dopant may be used without particular limitation as long as it is conventionally used in the art, for example, 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM). ) Can be used. The dopant serves to maintain the difference between the energy levels of the hole transport layer and the electron transport layer. Referring to FIG. 2, the tris (8-hydroxyquinoline) aluminum (Alq ₃ ) is 4--used when used alone. It can be seen that the energy gap (Gap) becomes smaller when (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM) is used. In the case of doping with DCM as described above, cluster beam deposition may be performed simultaneously by using an Alq ₃ and a separate crucible.

A method of manufacturing an organic light emitting display panel according to the present invention includes the steps of: (a) forming a buffer layer on a substrate; (b) forming a hole transporting layer by laminating a nanocomposite comprising MEH-PPV and 0.2-0.5% by weight single-wall carbon nanotubes based on the MEH-PPV on top of the buffer layer; And (c) forming a cathode on top of the hole transport layer.

As described above, the cathode may be made of gold (Au), the buffer layer may be a PEDOT: PSS layer, the thickness of the hole transport layer may be 400 to 600Å.

In the method of manufacturing an organic light emitting display panel according to the present invention, the step of forming a buffer layer by coating PEDOT: PSS on a substrate coated with ITO may use a conventional coating method, for example, spin coating or the like. The coating can be performed. Next, the step of laminating a nanocomposite containing 0.2 to 0.5% by weight of single-wall carbon nanotubes based on MEH-PPV and the MEH-PPV on the buffer layer is also a common coating method used in the art. It can be used without any limitation, and can be formed by spin coating or the like.

In addition, as described above, the method of manufacturing an organic light emitting display panel according to the present invention may further include forming an electron transport layer including tris (8-hydroxyquinoline) aluminum (Alq ₃ ) on the hole transport layer. The electron transport layer may further include 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM).

In the method of manufacturing an organic light emitting display panel according to the present invention, a thin film having excellent hole mobility and surface properties can be formed by depositing Alq ₃ , which is an electron transporting layer forming material, and DCM, which is a dopant, on a room temperature substrate using a cluster beam deposition method. .

In detail, the forming of the electron transport layer may include vaporizing the Alq ₃ by heating a crucible containing the Alq ₃ by applying a voltage; Allowing the Alq ₃ vapor to pass through the nozzle above the crucible to form a cluster; And depositing the Alq ₃ vapor on the hole transporting layer to form an electron transporting layer. In the case of the cluster beam deposition method, the film formed may have uniformity in film formation and electrons since the deposition buffer layer is room temperature. There is an advantage that the mobility is excellent.

On the other hand, it is preferable that the temperature in the step of vaporizing tris (8-hydroxyquinoline) aluminum (Alq ₃ ) as the electron transporting layer is 250 to 300 ° C., but if the temperature is less than 250 ° C., it may be difficult to vaporize. If the temperature exceeds 300 ° C., the surface roughness may be poor, which is not preferable.

In addition, the deposition rate during the cluster beam deposition according to the present invention is preferably 1 to 2 Å / s, when the deposition rate is less than 1 Å / s because the deposition rate of the thin film is too slow, it is difficult to form a thin film properly 2 Å / s When exceeding, since the roughness of the manufactured thin film may be inferior, it is not preferable. The deposition rate can be controlled by the temperature of the crucible.

In the cluster beam deposition apparatus used to manufacture the organic light emitting display panel according to the present invention, since the molecules in the vapor state pass through the nozzle located in the crucible cover, the clusters are formed by the collision between the molecules and form a beam having a directional beam. It is worn. According to the conventional chemical vapor deposition (CVD) method, the molecules to be deposited are deposited individually, so that the surface has a rough island shape. In the case of cluster beam deposition, clusters coupled with weak dispersion force are applied to the substrate. It is advantageous in that a thin film is formed evenly on the surface because it is broken during collision and distributed evenly on the substrate. The advantages of using a cluster beam are the high directivity and the translational kinetic energy of the beam obtained when the gas molecules are adiabaticly expanded in a high vacuum state.

Looking at the cluster beam deposition apparatus used in the present invention, the substrate is placed on top, the thickness monitor installed to measure the thickness of the deposited material in the deposition rate and thickness of the deposit in Å / s and k Å unit, respectively The thickness of the film can be monitored and the appropriate thickness can be adjusted. In addition, since the ammeter is connected to the substrate and grounded, the voltage of the substrate is 0V, unlike the application of a negative voltage to the substrate in the prior art. On the other hand, the shutter is provided to open and close from the outside and is initially closed, and is provided to be rotated from the outside when a constant deposition rate is reached to prevent the deposition of unpurified impurities. The variable voltage circuit is connected to apply a voltage to the crucible portion to form a potential difference with the substrate, and the terminal thereof is grounded.

Hereinafter, the present invention will be described in more detail with reference to preferred embodiments of the present invention, but the present invention is not limited thereto.

Example 1

High-purity single-walled carbon nanotubes were prepared using laser ablation and then evenly dispersed in a chlorobenzene solvent using an ultrasonic vibrator for 24 hours. Next, pure MEH-PPV was mixed with the carbon nanotubes to prepare a nanocomposite in which carbon nanotubes were mixed at 0.2 wt%. Subsequently, a PEDOT: PSS buffer layer was laminated on the glass substrate coated with ITO using spin coating, and the nanocomposite prepared above was deposited on the buffer layer using spin coating. Finally, gold was deposited on top of the nanocomposite layer using a thermal heating method to fabricate a device that moves only holes.

Example 2

A device was manufactured in the same manner as in Example 1, except that the content of carbon nanotubes in the nanocomposite was 0.5 wt%.

Example 3

High-purity single-walled carbon nanotubes were prepared using laser ablation and then evenly dispersed in a chlorobenzene solvent using an ultrasonic vibrator for 24 hours. Next, pure MEH-PPV was mixed with the carbon nanotubes to prepare nanocomposites containing 0.2 wt% of carbon nanotubes. Thereafter, a PEDOT: PSS buffer layer was laminated on the glass substrate coated with ITO using spin coating, and the nanocomposite prepared above was deposited on the buffer layer using spin coating. Next, a vacuum in the deposition chamber was maintained at 3 × 10 ⁻⁶ Torr using a 10 inch diffusion pump with a baffle. Inside the deposition chamber, the crucible and the drift region of the graphite material and the substrate on which the composite layer prepared above were formed were placed on top. The distance between the crucible and the substrate was set to 190 mm. A tris (8-hydroxyquinoline) aluminum (Alq ₃ ) is placed inside the crucible, and thermally expanded through a nozzle having a hole of about 1 mm while maintaining an electrical resistance method of 260 ° C. in the upper portion of the hole transport layer. , Alq ₃ An electron transport layer was formed to a thickness of 400 Å so that neutral clusters were formed. Finally, a heterojunction device was manufactured by depositing a Li: Al alloy to be used as a cathode by thermal heating.

Example 4

A device was manufactured in the same manner as in Example 3, except that the content of carbon nanotubes in the nanocomposite was 0.5 wt%.

Example 5

When depositing the electron transporting layer, a different crucible was provided inside the same deposition chamber, and 4- (dimethylaminomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM) was loaded. A device was manufactured in the same manner as in Example 3, except that Alq ₃ and DCM were simultaneously deposited together by co-deposition.

Example 6

A device was manufactured in the same manner as in Example 5, except that the content of carbon nanotubes in the nanocomposite was 0.5 wt%.

Comparative Example 1

A device was manufactured in the same manner as in Example 1, except that only MEH-PPV was used as the hole transport layer.

Comparative Example 2

A device was manufactured in the same manner as in Example 1, except that the content of carbon nanotubes in the nanocomposite was 1% by weight.

Comparative Example 3

A device was manufactured in the same manner as in Example 5, except that only MEH-PPV was used as the hole transport layer.

Comparative Example 4

A device was manufactured in the same manner as in Example 5, except that the content of carbon nanotubes in the nanocomposite was 1 wt%.

Test Example 1

Measurement of Current Voltage Characteristics

The current and voltage characteristics of the device moving only the holes manufactured according to Examples 1 and 2 and Comparative Examples 1 and 2 were measured and the results are shown in FIG. 3. Referring to FIG. 3, it can be seen that as the amount of nanotubes increases, the current density increases and the turn-on voltage decreases.

Test Example 2

Standardized Photoluminescence (PL) Electroluminescence (EL) value  Measure

The values for PL and EL of the organic light emitting display panels manufactured in Examples 3 and 5 were measured and shown in FIG. 4. Referring to FIG. 4, typical photoluminescence (photoluminescence) and electroluminescence (electroluminescence) spectra of DCM doped and undoped OLEDs are shown. In the case of doping, the complete energy transfer from Alq ₃ to DCM occurs and thus only light is emitted from DCM.

Test Example 3

Electrical property measurement

Values of current, voltage, light intensity, and efficiency of the organic light emitting diode panels manufactured by Examples 5 and 6 and Comparative Examples 3 and 4 were measured and shown in FIGS. 5A and 5B. Referring to FIG. 5A, it can be seen that as the content of the nanotube increases, the current density increases and the turn-on voltage decreases. However, referring to FIG. 5B, when the content of the carbon nanotube exceeds 0.5% by weight, the external quantum It can be seen that the efficiency is lowered due to the nonuniformity of holes and electrons due to the presence of nanotubes.

As described above, the organic light emitting display panel according to the present invention has an advantage of excellent device performance due to high current density and low turn-on voltage because of excellent hole mobility.

Claims (15)

An anode formed on the substrate; An organic film formed on the anode; And a cathode formed on an upper portion of the organic layer. The organic layer includes a buffer layer, a hole transport layer, and a light emitting layer sequentially stacked from the bottom, The hole transport layer includes 0.2 to 0.5 wt% single-walled carbon nanotubes based on MEH-PPV and MEH-PPV, and has a thickness of 400 to 600 kPa. The method of claim 1, And the cathode is made of gold (Au). The method of claim 1, And the buffer layer is a PEDOT: PSS layer. delete The method of claim 1, And an electron transport layer including tris (8-hydroxyquinoline) aluminum (Alq ₃ ) on the hole transport layer. The method of claim 5, wherein The electron transport layer further comprises 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM). (a) forming a buffer layer on the substrate; (b) forming a hole transporting layer by laminating a nanocomposite comprising 0.2 to 0.5% by weight of single-wall carbon nanotubes based on MEH-PPV and the MEH-PPV to a thickness of 400 to 600 mm on top of the buffer layer. ; And (c) forming a cathode on the hole transport layer. The method of claim 7, wherein And the cathode is made of gold (Au). The method of claim 7, wherein The buffer layer is a manufacturing method of an organic light emitting display panel, characterized in that the PEDOT: PSS layer. delete The method of claim 7, wherein And forming an electron transporting layer comprising tris (8-hydroxyquinoline) aluminum (Alq ₃ ) on the hole transporting layer. The method of claim 11, The electron transport layer further comprises 4- (dicyanomethylene) -2-methyl-6- (p-dimethylaminostyryl) -4H-pyran (DCM). . The method of claim 11, The forming of the electron transport layer may include vaporizing the Alq ₃ by heating a crucible containing the Alq ₃ by applying a voltage; Allowing the Alq ₃ vapor to pass through the nozzle above the crucible to form a cluster; And depositing the Alq ₃ vapor on the hole transport layer to form an electron transport layer. The method of claim 13, The temperature of the crucible is 250 to 300 ℃ manufacturing method of an organic light emitting display panel. The method of claim 13, And the deposition rate is in the range of 1 to 2 GHz / sec.

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