KR101634647B1 - Polymer light emitting diode and method thereof - Google Patents

Abstract

The present invention relates to a polymer light emitting diode and a manufacturing method thereof.
According to the present invention, there is provided a polymer light emitting diode (LED) using a buffer layer comprising an electrode comprising an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor, A high-temperature sputtering process which is a problem of a conventional ITO transparent electrode is required, surface roughness is poor, difficulty in fabricating a flexible device due to high crystallinity, low luminance and stability, and high luminance , It is possible to provide a polymer light emitting diode having a long lifetime as well as being capable of being applied to a large-area surface light source as well as capable of flexible lighting as well as reducing power consumption by improving power efficiency.

Description

TECHNICAL FIELD [0001] The present invention relates to a polymer light emitting diode (LED)

The present invention relates to a polymer light emitting diode and a method of fabricating the same, and more particularly, to a polymer light emitting diode and a method of fabricating the same. More particularly, the present invention relates to a polymer having a buffer layer containing an electrode comprising an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor Emitting diode and a method of manufacturing the same.

A thin film having a light transmittance of 80% or more with respect to the visible light region (wavelength region of 380 to 780 nm) and having a specific resistance of 10 -3? Cm or less is referred to as a transparent conducting oxide (TCO) film.

The TCO can be applied to various flat panel displays (FPD) such as liquid crystal display (LCD), organic light emitting diode (OLED) and the like as well as thin film solar cell, touch panel screen , TPS) are widely used as transparent electrode materials in various optoelectronic devices.

As a result, there have been a lot of studies on transparent electrode materials which are currently being studied, such as cadmium, tin, indium, zinc, and gallium. As the transparent electrode to which these materials are applied, Fluorine-doped tin oxide (FTO), cadmium stannate (CTO), and indium tin oxide (ITO). Among them, the ITO thin film doped with indium oxide (In2O3) with tin oxide has a low resistance and is transparent and is mainly used as a transparent electrode material.

Typically, the ITO thin film is prepared by sputtering a target made of In 2 O 3 and SnO 2 in a composition of 9: 1 (wt%) on a glass substrate. However, as the optoelectronic device market expands explosively, the demand for ITO is increasing, but the reserves of indium, a rare metal, are declining, so prices are rising every year.

In order to have a low resistivity and a high light transmittance, a high temperature film forming process of 300 DEG C or more is required, but a high process temperature lowers the etching characteristics during patterning of the transparent electrode, and due to the rough surface roughness depending on the irregular crystal growth rate It has a disadvantage that it is difficult to apply to a flexible substrate having a low glass transition temperature (Tg) such as polyethylene terephthalate (PET), polycarbonate (PC) and the like. In addition, the thin film produced through the high temperature film forming process has crystallinity, so that the thin film is easily broken when the substrate is warped or bent.

Recently, a technique for fabricating a transparent electrode using a transparent conductive polymer material, a carbon nanotube (CNT), or graphene has been researched. However, The transparent electrode has a disadvantage that it has a low conductivity and a high specific resistance. In the case of a carbon-based transparent electrode such as carbon nanotube and graphene, it is difficult to mass-produce and form a high-quality thin film having a large area.

On the other hand, in the case of a polymer light emitting diode using an electroluminescent polymer as an active layer, it is possible to manufacture a large-area device through a solution process such as a roll-to-roll process as compared with a low-molecular light emitting diode using a vacuum deposition process, Mass production is possible.

However, the brightness and stability of a polymer light emitting diode is lower than that of a low molecular weight light emitting diode.

Prior art related to the present invention includes Korean Patent Laid-Open No. 10-2012-0127506 (flexible display device and its manufacturing method), Japanese Patent No. 4846726 (sputtering target, transparent conductive film and transparent electrode), and the like.

The present inventors have found that a polymer light emitting diode (OLED) using a buffer layer including an electrode comprising an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor exhibits a higher luminance than a general polymer light emitting diode, As a result, it is possible to solve the problem of short lifetime, which is considered to be a disadvantage of conventional polymer light emitting diodes. The present invention has been completed.

It is an object of the present invention to provide a polymer light emitting diode using a buffer layer including an electrode including an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor.

Another object of the present invention is to provide a method of fabricating a polymer light emitting diode (LED) using a buffer layer comprising an electrode comprising an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor.

According to an aspect of the present invention, there is provided a plasma display panel comprising: a substrate; a first electrode including an IZTO (indium zinc tin oxide) thin film disposed on the substrate; a hole transport layer disposed above the first electrode; A buffer layer comprising a polymer luminescent layer disposed on the transport layer and a zinc oxide precursor disposed on the polymer luminescent layer; And a second electrode disposed on the buffer layer.

Wherein the substrate is a glass substrate or a flexible substrate.

The IZTO is characterized by containing 40 to 80 wt% of In ₂ O ₃ , 10 to 30 wt% of ZnO, and 10 to 30 wt% of SnO ₂ .

And the polymer light emitting layer is disposed at 10 to 150 nm.

The buffer layer is formed by mixing zinc oxide precursor and methanol in a weight ratio of 1: 1 to 1: 200.

The second electrode may be formed of a material selected from the group consisting of lithium fluoride / aluminum, lithium fluoride / calcium / aluminum, calcium / aluminum, barium fluoride / aluminum, barium fluoride / barium / aluminum, barium / aluminum, aluminum, gold, silver / . ≪ / RTI >

The present invention also provides a method for fabricating a polymer light emitting diode, comprising: forming an IZTO thin film on a substrate; and forming a buffer layer including a zinc oxide precursor on the polymer light emitting layer.

The IZTO is characterized by containing 40 to 80 wt% of In ₂ O ₃ , 10 to 30 wt% of ZnO, and 10 to 30 wt% of SnO ₂ .

The buffer layer is formed by mixing a zinc oxide precursor with methanol at a weight ratio of 1: 1 to 1: 200.

According to the present invention, there is provided a polymer light emitting diode (LED) using a buffer layer comprising an electrode comprising an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor, A high-temperature sputtering process which is a problem of a conventional ITO transparent electrode is required, surface roughness is poor, difficulty in fabricating a flexible device due to high crystallinity, low luminance and stability, and high luminance , It is possible to provide a polymer light emitting diode having a long lifetime as well as being capable of being applied to a large-area surface light source as well as capable of flexible lighting as well as reducing power consumption by improving power efficiency.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a polymer light emitting diode in which a buffer layer including an electrode including an indium zinc tin oxide (IZTO) thin film according to the present invention and a zinc oxide precursor (ZnO precursor) is introduced.
Figure 2 shows an optimized pattern shape of an electrode comprising an indium zinc tin oxide (IZTO) thin film.
FIG. 3 is a graph showing IV characteristics of a polymer light emitting diode according to whether or not a buffer layer including an electrode including an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor is introduced.
FIG. 4 is a graph showing stability results of a polymer light emitting diode according to whether or not a buffer layer including an electrode including an IZTO (indium zinc tin oxide) thin film and a zinc oxide precursor is introduced.

Hereinafter, the present invention will be described in detail.

The first electrode includes an IZTO (indium zinc tin oxide) thin film disposed on the substrate, a hole transport layer disposed on the first electrode, and a polymer light emitting layer disposed on the hole transport layer. And a zinc oxide precursor (ZnO precursor) disposed on the polymer light emitting layer; And a second electrode disposed on the buffer layer.

The present invention also provides a method for fabricating a polymer light emitting diode, comprising: forming an IZTO thin film on a substrate; and forming a buffer layer including a zinc oxide precursor on the polymer light emitting layer. (1) forming a first electrode including an IZTO (indium zinc tin oxide) thin film on a substrate; and (2) forming a first electrode (3) forming a polymer light emitting layer on the hole transport layer, and (4) forming a buffer layer including a zinc oxide precursor on the polymer light emitting layer. And (5) forming a second electrode on the buffer layer.

As shown in FIG. 1 showing a schematic structure of a polymer light emitting diode manufactured according to a preferred embodiment of the present invention, a substrate 110, a first electrode 120, a hole transport layer 130, a polymer light emitting layer A buffer layer 150 including a ZnO precursor, and a second electrode 160 are stacked.

In the present invention, the substrate 110 used in the production of the polymer light emitting diode may be made of PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PP (polypropylene), PI (polyimide), PC (pilycarbornate) such as plastics, such as polystyrene, polystyrene, POM (polyoxyethylene), AS resin, ABS resin, and TAC (triacetyl cellulose). PI substrates are used in the present invention.

On the other hand, the glass substrate or the flexible substrate is sequentially cleaned with a cleaning agent, acetone and isopropanol (IPA), and then dried on a heating plate at 100 to 150 ° C for 1 to 30 minutes, preferably 110 ° C for 10 minutes, When the substrate is completely cleaned, it is preferable to modify the surface of the substrate to be hydrophilic. Through such surface modification, the bonding surface potential can be maintained at a level suitable for the surface potential of the hole transport layer, the thin film can be easily formed at the time of modification, and the quality of the thin film can be improved. As a pretreatment technique for this purpose, i) a surface oxidation method using a parallel plate discharge, ii) a method of oxidizing the surface through ozone generated by using ultraviolet rays in a vacuum state, iii) a method of oxidizing the surface by using oxygen radicals generated by plasma Oxidation method. Depending on the state of the substrate, one of the above methods may be selected. In any case, it is necessary to prevent oxygen escape from the surface of the substrate and to keep the moisture and organic matter as much as possible. You can expect.

Accordingly, in the present invention, a method of oxidizing the surface through ozone generated using UV ultraviolet rays is used. After the ultrasonic cleaning, the substrate is baked in an oven, dried, transferred to a chamber, The substrate is cleaned by ozone generated by reaction with UV light. However, in the present invention, the method of modifying the surface of the substrate is not particularly limited, and any method may be used as long as it is a method of oxidizing the substrate.

The first electrode 120 may be formed by depositing an electrode material containing an indium zinc tin oxide (IZTO) thin film using sputtering, E-beam, thermal evaporation, spin coating, screen printing, inkjet printing, doctor blade or gravure printing By coating on one side of the substrate or by coating in the form of a film. The first electrode 120 functions as an anode and may be made of any material having a higher work function than the second electrode 160 and having transparency and conductivity. For example, a metal oxide such as ITO (indium tin oxide), gold, silver, fluorine doped tin oxide (FTO), aluminum doped zink oxide (AZO), indium zink oxide ), ZnO-Ga ₂ O ₃ , ZnO-Al ₂ O _3, and ATO (antimony tin oxide).

In the present invention, the first electrode 120 is made of IZTO (indium zinc tin oxide), and is designed to have a composition of 40 to 80 wt% of In ₂ O ₃ , 10 to 30 wt% of SnO _{2, and} 10 to 30 wt% of ZnO It is more preferable to use a composition of 80 wt% of In ₂ O ₃ , 10 wt% of SnO _{2, and} 10 wt% of ZnO.

When the IZTO target is sputtered, it is desirable to heat the substrate at a temperature ranging from room temperature to 100 ° C, more preferably room temperature. On the other hand, the partial pressure of oxygen injected together with argon (Ar) during the sputtering is preferably 0 to 10%, more preferably 0 to 4%.

The IZTO transparent electrode according to the present invention is fabricated by patterning a substrate on which IZTO is deposited, which is the first electrode 120, and a hole transport layer 130 is formed on the first electrode 120 by spin coating or dip coating Poly (3,4-ethylenedioxythiophene): poly (4-styrenesulfonate) [PEDOT: PSS] is preferably used as the conductive polymer solution in the present invention.

The polymer luminescent layer (140) of the present invention was a green polymer of Merck, Germany. The light emitting layer materials are dissolved in an organic solvent, and a polymer luminescent layer is preferably introduced into the solution in which two or more breaking points are dissolved in another organic solvent by spin coating to a thickness of 10 to 150 nm, preferably 60 to 120 nm . At this time, dip coating, screen printing, spray coating, doctor blade, brush painting and the like can be applied to the polymer light emitting layer.

The buffer layer 150 including the ZnO precursor introduced for improving the brightness and stability of the present invention is prepared by synthesizing a zinc oxide precursor and then diluting it to an arbitrary concentration. The ZnO precursor was prepared by mixing 10 ml of 2-methoxy ethanol and 0.379 g of zinc acetate into a flask and stirring. Then, 0.0528 g of ethanol amine was added thereto, And the mixture was stirred for 2 hours. A zinc oxide precursor (methanol: ZnO precursor: methanol) was added at a weight ratio of 1: 1 to 1: 200, preferably 1:30 to 1: 1, before forming a buffer layer containing a zinc oxide precursor : 70, and introduced into the upper part of the polymer light emitting layer. At this time, the ZnO layer can be applied by dip coating, screen printing, spray coating, doctor blade, brush painting or the like.

The second electrode 160 is deposited in a thermal evaporator having a degree of vacuum of 5 × 10 ^-7 torr or less in a state where the buffer layer 150 including a zinc oxide precursor is introduced. The electrode material usable herein may be lithium fluoride / aluminum, lithium fluoride / calcium / aluminum, calcium / aluminum, barium fluoride / aluminum, barium fluoride / barium / aluminum, barium / aluminum, aluminum, gold, silver, Or lithium: aluminum, and it is preferable to use an electrode made of a barium / aluminum structure. Barium (Ba), and aluminum (Al), respectively, by vacuum deposition.

Hereinafter, the present invention will be described in more detail with reference to Examples. It should be apparent to those skilled in the art that these embodiments are for illustrative purposes only and that the scope of the present invention is not construed as being limited by these examples

Example 1. Substrate cleaning

To clean the surface of the PI (100 μm thick, MISSBY Gas Chemical, Japan) substrate, ultrasonic cleaning was performed for 5 minutes each in the order of a cleaning agent (Alconox, Aldrich, USA), acetone and isopropyl alcohol, And dried on a hot plate at 110 DEG C for 10 minutes to remove moisture.

Once the PI substrate was thoroughly cleaned, the surface was hydrophilically modified for 10 minutes in a UVO scrubber (UVO cleaner, Ahtech LTS, Korea).

Example 2 Preparation of an electrode comprising an IZTO (indium zinc tin oxide) thin film

The composition of the electrode including the IZTO thin film according to the present invention was designed to have a composition of 40 to 80 wt% of In 2 O 3, 10 to 30 wt% of SnO 2, and 10 to 30 wt% of ZnO. The PI substrate was fabricated by the room temperature film formation process when the electrode including the IZTO thin film was deposited by the sputtering method.

In preparing the electrode including the IZTO thin film according to the present invention, the partial pressure of oxygen injected with argon (Ar) was 3%.

The sheet resistance of the prepared PI IZTO transparent electrode was 20? / Sq and the light transmittance was 82%.

Example 3. Patterning of an electrode comprising an indium zinc oxide thin film (IZTO) thin film

In order to establish the patterning condition of PI IZTO transparent electrode of In0.8Zn0.1Sn0.1 composition, optimization experiment was performed. A PR (photo resist) film having a thickness of about 300 nm (spin coating: 4000 rpm) was formed on the cleaned PI IZTO transparent electrode and heat-treated at 80 to 100 ° C for 5 to 15 minutes. Then, the exposure time of the coated PR was set to 55 to 70 seconds. The exposed PR was set at a development time of 20 seconds to 25 seconds, and the etching time was set to 20 seconds to 30 seconds. Patterned IZTO was examined through an optical microscope to establish patterning conditions. Figure 2 shows the IZTO transparent electrode patterned under optimized conditions.

Example 4 Preparation of a Polymer Light Emitting Diode Including a PI-based IZTO Thin Film and a Buffer Layer Including a ZnO Precursor

Using the patterned PI-based IZTO transparent electrode fabricated in Example 3, a polymer light emitting diode was fabricated under the following conditions.

Specifically, the major transport layer material PEDOT: PSS was filtered with a 0.45 μm PTFE syringe filter and stirred for 24 hours. The green polymer used as the polymer light emitting layer was dissolved in chlorobenzene at a concentration of 0.5 wt% and stirred for 24 hours. And then filtered using a 0.45 [mu] m PVDF syringe filter. The buffer layer containing ZnO precursor was mixed with methanol at a ratio of 1:50 and stirred for 12 hours and filtered using a 0.2 μm PVDF syringe filter.

The device was fabricated with a structure of PI / IZTO (200 nm) / PEDOT: PSS (40 nm) / Green polymer (80 nm) / ZnO (10 nm) / Ba (2 nm) / Al (200 nm).

PEDOT: PSS was annealed at 140 ° C for 10 minutes, the polymer luminescent layer was annealed at 80 ° C for 30 minutes, and ZnO was annealed at 100 ° C for 1 hour. Thereafter, the substrate was transferred to a high vacuum chamber (1 × 10 -6 torr or less) of a thermal evaporator, and Ba (0.2 Å / s, 2 nm) and Al (5 Å / s, 200 nm) .

Example 5. Fabrication of Polymer Light Emitting Diodes Incorporating Electrodes Containing Glass-based ITO Thin Films

A polymer light emitting diode was manufactured by the same method and conditions as in Example 4, except that a glass-based ITO thin film was introduced into a transparent electrode.

Comparison 1. Fabrication of Polymer Light Emitting Diodes without introducing a buffer layer containing ZnO precursor by introducing an electrode containing a PI-based IZTO thin film

Polymer light emitting diodes were prepared according to the same method and conditions as in Example 4, except that a buffer layer containing a zinc oxide precursor was not inserted.

Comparative Example 2. Fabrication of a polymer light-emitting diode without introducing a buffer layer containing a ZnO precursor by introducing an electrode including a glass-based ITO thin film

A polymer light emitting diode was prepared by the same method and conditions as in Example 4 except that a glass-based ITO thin film was introduced as a transparent electrode and a buffer layer containing a zinc oxide precursor was not inserted.

Experimental Example 1. Evaluation of Polymer Light Emitting Diode Characteristics

The luminance-voltage characteristics of the polymer LED according to the present invention are measured and shown in FIG. 4 shows stability test results of the buffer layer including a zinc oxide precursor (ZnO precursor) of a polymer LED employing an electrode including an IZTO thin film.

[Table 1]

As a result, devices using electrodes including ITO and IZTO thin films and devices with a buffer layer containing zinc oxide precursor (ZnO precursor) were turned on at 3 V, and zinc oxide precursor The maximum luminance of Example 5 in which a buffer layer containing a ZnO precursor was introduced into an ITO transparent electrode was higher than the maximum luminance of 20042 cd / cm 2 in Comparative Example 2 in which a buffer layer including a ZnO precursor was not introduced 32800 cd / cm < 2 >. This was the same in the case of using IZTO as a transparent electrode. Comparing Example 4 with Comparative Example 1, it can be seen that the luminance of Example 4 in which a buffer layer containing a zinc oxide precursor is applied is improved. Particularly, it was found that the stability of the device using the IZTO transparent electrode after the application of the buffer layer containing the zinc oxide precursor (FIG. 4)

Also, when comparing Comparative Examples 1 and 2, it can be seen that the brightness of the device applied to the PI-based IZTO is brighter than that of the polymer light emitting device applied to the glass-based ITO. Therefore, by applying IZTO transparent electrode applicable to flexible substrate at room temperature process, it is possible to lower the production cost compared with glass-based ITO manufactured through conventional high temperature process, and stability of device can be improved by introducing ZnO as solution process There is an advantage.

Having described specific portions of the present invention in detail, those skilled in the art will appreciate that these specific embodiments are merely preferred embodiments and that the scope of the present invention is not limited thereby. something to do. Accordingly, the actual scope of the present invention will be defined by the appended claims and their equivalents.

Claims (9)

Board;
A first electrode comprising an IZTO (indium zinc tin oxide) thin film disposed on the substrate;
A hole transport layer disposed on the first electrode;
A polymer light emitting layer disposed on the hole transport layer;
A buffer layer including a zinc oxide precursor disposed on the polymer light emitting layer; And
And a second electrode disposed on the buffer layer,
Wherein the buffer layer is formed by mixing a zinc oxide precursor and methanol in a weight ratio of 1:50.
The method according to claim 1,
Wherein the substrate is a glass substrate or a flexible substrate.
The method according to claim 1,
Wherein the IZTO comprises 40 to 80 wt% of In ₂ O ₃ , 10 to 30 wt% of ZnO, and 10 to 30 wt% of SnO ₂ .
The method according to claim 1,
Wherein the polymer light emitting layer is disposed at 10 to 150 nm.
delete The method according to claim 1,
The second electrode may be formed of a material selected from the group consisting of lithium fluoride / aluminum, lithium fluoride / calcium / aluminum, calcium / aluminum, barium fluoride / aluminum, barium fluoride / barium / aluminum, barium / aluminum, aluminum, gold, silver / Wherein the polymer is selected from the group consisting of:
Forming an IZTO thin film on the substrate, and forming a buffer layer including a zinc oxide precursor on the polymer light emitting layer,
Wherein the buffer layer is formed by mixing zinc oxide precursor and methanol in a weight ratio of 1:50.
8. The method of claim 7,
Wherein the IZTO comprises 40 to 80 wt% of In ₂ O ₃ , 10 to 30 wt% of ZnO, and 10 to 30 wt% of SnO ₂ .
delete

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