Organic light emitting diode and organic light emitting display having the same

An organic light emitting diode that can improve a driving voltage and emission efficiency includes a first electrode, an organic layer formed on the first electrode and including an emitting layer and an electron transport layer that is doped with an organic n-type impurity, and a second electrode formed on the organic layer. The electron transport layer is made of C60. An organic light emitting display includes the organic light emitting diode.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No. 2006-115145 filed on Nov. 21, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Aspects of the present invention relate to an organic light emitting diode, and more particularly, to an organic light emitting diode that can improve a driving voltage and emission efficiency and an organic light emitting display having the same.

2. Description of the Related Art

An organic light emitting display is a self-emitting display using a phenomenon in which electrons and holes injected into an organic material through an anode and a cathode are recombined to form excitons, thereby causing a light beam with a specific wavelength to be generated by the energy of the formed excitons. The organic light emitting display does not require a separate light source such as a backlight, and therefore has a low power consumption. Furthermore, since a wide viewing angle and a fast response time can be easily ensured, the organic light emitting display is promising as a next generation display.

In terms of a driving method, organic light emitting displays are classified into a passive matrix type and an active matrix type. In recent years, the active matrix type has become more popular than the passive matrix type because of advantages in low power consumption, high definition, fast response time, wide viewing angle, and thinness and lightness.

In such an active matrix type organic light emitting display, a pixel region is formed on a substrate so as to display an actual image, and pixels, each of which is a basic unit of an image, are arranged in a matrix form. An organic light emitting diode is disposed for each pixel. The organic light emitting diode is constructed such that a first pixel electrode (anode) and a second pixel electrode (cathode) are sequentially formed with an emitting layer including a red (R), green (G), or blue (B) organic material interposed therebetween. A thin film transistor (TFT) is in contact with the organic light emitting diode for each pixel so that each pixel can be separately controlled.

A driving voltage of the organic light emitting display depends on the first pixel electrode, the emitting layer, and the second pixel electrode forming the organic light emitting diode. With larger sized organic light emitting displays with higher brightness, the driving voltage as well as power consumption increases. Therefore, an interface of the organic light emitting diode has to be regulated so as to effectively transport electrons and holes.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an organic light emitting diode that can improve the driving voltage and emission efficiency of the diode.

Aspects of the present invention also provide an organic light emitting display having the organic light emitting diode mentioned above and capable of reducing power consumption.

According to an embodiment of the invention, there is provided an organic light emitting diode comprising a first electrode, an organic layer formed on the first electrode and including an emitting layer and an electron transport layer comprising C60 that is doped with an organic n-type impurity, and a second electrode formed on the organic layer.

According to an aspect of the present invention, the organic n-type impurity may be pyronine B or dicarbocyanine iodide.

According to an aspect of the present invention, the electron transport layer may have a thickness in a range of 100 Å to 400 Å.

According to another embodiment of the invention, there is provided an organic light emitting diode comprising a first electrode, an organic layer formed on the first electrode and including the following layers sequentially laminated: a hole injection layer, a hole transport layer, a emitting layer, and a doped electron transport layer comprising C60 doped with an organic n-type impurity, and a second electrode formed on the organic layer.

According to an aspect of the present invention, the organic n-type impurity is pyronine B or dicarbocyanine iodide.

According to an aspect of the present invention, the electron transport layer may have a thickness in a range of 100 Å to 400 Å.

According to an aspect of the present invention, the organic layer may further comprise an electron injection layer formed between the doped electron transport layer and the second electrode. The electron injection layer may be made of a material selected from a group consisting of Li, Cs, Mg, BaF2, LiF, NaCl, CsF, Li2O, BaO, CaF2, Cs2CO3, Cs2O, CaO, MgF2, MgO, and Liq.

According to an aspect of the present invention, the organic layer may further comprise an undoped electron transport layer formed between the doped electron transport layer and the second electrode.

According to an aspect of the present invention, the organic layer may further comprise a first undoped electron transport layer formed between the doped electron transport layer and the emitting layer, and a second undoped electron transport layer formed between the doped electron transport layer and the second electrode.

According to another embodiment of the invention, there is provided an organic light emitting display comprising a substrate, and an organic light emitting diode formed on the substrate and including a first electrode, an organic layer formed on the first electrode and in which the following layers are sequentially laminated: a hole injection layer, a hole transport layer, an emitting layer, and a doped electron transport layer comprising C60 doped with an organic n-type impurity, and a second electrode formed on the organic layer.

According to an aspect of the present invention, the organic n-type impurity may be pyronine B or dicarbocyanine iodide.

According to an aspect of the present invention, the electron transport layer may have a thickness in a range of 100 Å to 400 Å.

According to an aspect of the present invention, the organic layer may further comprise an electron injection layer formed between the doped electron transport layer and the second electrode. The electron injection layer may be made of a material selected from a group consisting of Li, Cs, Mg, BaF2, LiF, NaCl, CsF, Li2O, BaO, CaF2, Cs2CO3, Cs2O, CaO, MgF2, MgO, and Liq.

According to an aspect of the present invention, the organic layer may further comprise an undoped electron transport layer formed between the doped electron transport layer and the second electrode.

According to an aspect of the present invention, the organic layer may further comprise a first undoped electron transport layer formed between the doped electron transport layer and the emitting layer, and a second undoped electron transport layer formed between the doped electron transport layer and the second electrode.

According to an aspect of the present invention, the organic light emitting display may further comprise a thin film transistor electrically connected to the organic light emitting diode and formed on the substrate.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. As those skilled in the art would realize, the described embodiments may be modified in various different ways, all without departing from the spirit or scope of the present invention.

Referring toFIG. 1, an organic light emitting diode L1includes a first electrode310(for example, an anode), an organic layer330, and a second electrode340(for example, a cathode), which are sequentially laminated. The organic layer330may have a structure in which multi-layered organic thin films are laminated. For example, the multilayered organic thin films may include a hole injection layer (HIL)331, a hole transport layer (HTL)332, an emitting layer (EML)333, and an electron transport layer (ETL)334doped with an organic n-type impurity, which are sequentially laminated.

The first electrode310may be a first transparent electrode composed of indium tin oxide (ITO) or indium zinc oxide (IZO). According to an emission direction of the organic light emitting diode L1, a conductive reflection layer and a second transparent electrode may be further formed on the first transparent electrode. The reflection layer reflects light generated from the organic layer330so as to improve emission efficiency and electrical conductivity. For example, the reflection layer may be made of aluminum (Al), aluminum alloy (Al-alloy), silver (Ag), silver alloy (Ag-alloy), gold (Au), or gold alloy (Au-alloy). The second transparent electrode not only reduces oxidation of the reflection layer but also improves a work function relation between the organic layer330and the reflection layer. For example, the second transparent electrode may be made of ITO or IZO, the same as the first transparent electrode.

The second electrode340may be made of a transparent metallic oxide having an excellent conductivity, for example, indium tin oxide (ITO), indium zinc oxide (IZO), tin oxide (SnO2), or zinc oxide (ZnO). Alternatively, the second electrode340may be constructed with a transparent or reflective metallic thin film such as, for example, lithium (Li), magnesium (Mg), aluminum (Al), aluminum-lithium (Al—Li), calcium (Ca), magnesium-indium (Mg—In), magnesium-silver (Mg—Ag), or calcium-aluminum (Ca—Al). However, the present invention is not limited thereto.

Although the first electrode310is described herein as the anode and the second electrode340is described herein as the cathode, it is also possible for the first electrode310to function as a cathode, and the second electrode340to function as an anode.

The hole injection layer331and the hole transport layer332of the organic layer330effectively move holes injected from the first electrode210to the emitting layer333.

The hole injection layer331may be made of any known hole injection material, such as, for example, copper phthalocyanine (CuPc) or starburst-type amines. However, the embodiment of the present invention is not limited thereto. As non-limiting examples, the starburst-type amines may be 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) expressed by Chemical Formula 1, 4,4′,4″-tris(N-3-metylph-enyl-N-phenyl-amino)-triphenylamine (m-MTDATA) expressed by Chemical Formula 2, polyaniline/dodecylbenzenesulfonic acid (Pani/DBSA) expressed by Chemical Formula 3 and produced by Idemitsu (JP), or poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) expressed by Chemical Formula 4.

The hole transport layer332may be deposited by using a vacuum deposition method, a spin coating method, a cast method, or a Langmuir-Blodgett (LB) method. For example, when the vacuum deposition method or the spin coating method is used, the hole transport layer332may be deposited under the same deposition conditions as the hole injection layer331.

The emitting layer333may be made of a red (R), green (G), or blue (B) organic material.

Alternatively, a material including Alq3doped with a dopant such as DCJTB or a material including Alq3co-deposited with rubrene and doped with a dopant may be used for the R organic material. Alternatively, a material including 4,4′-N—N′-dicarbazole-biphenyl (CBP) doped with a dopant such as BTPIr may be used for the R organic material. However, the embodiment of the present invention is not limited thereto.

When the emitting layer333is made of a G organic material, coumarin 6, C545T, quinacridone, or Ir(ppy)3may be used. Alternatively, a material including CBP[4,4′-Bis(carbazol-9-yl)biphenyl] doped with a dopant such as Ir(ppy)3may be used for the G organic material. Further, a material including Alq3doped with a coumarin dopant may be used for a host. However, the embodiment of the present invention is not limited thereto. As non-limiting examples, the coumarin dopant may be C314S, C343S, C7, C7S, C6, C6S, C314T, or C545T.

When the emitting layer333is made of a B organic material, various materials may be used such as oxadiazole dimer dyes(such as, for example, Bis-DAPOXP), spiro compounds (such as, for example, Spiro-DPVBi or Spiro-6P), triarylamine compounds, bis(styryl)amine(DPVBi, DSA), compound (A), Flrpic, CzTT, anthracene, TPB, PPCP, DST, TPA, OXD-4, BBOT, AZM-Zn, or BH-013X (an aromatic hydrocarbon compound containing a naphthalene moiety, produced by Idemitsu (JP)) that is. Alternatively, a material including IDE140 (produced by Idemitsu (JP)) doped with a dopant such as IDE105 (produced by Idemitsu (JP)) may be used for the B organic material. However, the embodiment of the present invention is not limited thereto.

The emitting layer333may be made of a poly-phenylenevinylene (PPV) material or a polyfluorene material.

Further, the emitting layer333may have a thickness of 100 Å to 500 Å. As a specific, non-limiting example, the thickness may be 100 Å to 400 Å. The thickness may be adjusted within this range according to the material that constitutes the emitting layer333. The life-time may be shortened when the thickness of the emitting layer333is less than 200 Å. On the other hand, the driving voltage may increase sharply when the thickness of the emitting layer333is greater than 500 Å.

Although not shown, an exciton anti-quenching layer may be formed so as prevent an exciton from quenching. If present, the exciton anti-quenching layer should be made of a material having an electron transport capability and an ionization potential greater than that of the material that constitutes the emitting layer333. For example, the exciton anti-quenching layer may be made of Alq3, Bphen, bis(2-methyl-8-quinolato)-(p-phenylphenolato)-aluminum(Balq), C60, bathocuproine (BCP), or tris(N-arylbenzimidazole) (TPBI). If n-type impurities are not doped into the exciton anti-quenching layer, the exciton anti-quenching layer may have a thickness of 30 Å to 150 Å, preferably, 40 Å to 100 Å. The exciton anti-quenching efficiency may not be significant when the thickness of the exciton anti-quenching layer is less than 30 Å. On the other hand, the driving voltage may rise when the thickness thereof is greater than 150 Å.

The exciton anti-quenching layer may be deposited by using the vacuum deposition method, the spin coating method, or the LB method. For example, when the vacuum deposition method or the spin coating method is used to deposit the exciton anti-quenching layer, the exciton anti-quenching layer may be deposited under the same deposition conditions as the hole injection layer331.

In the electron transport layer334doped with an organic n-type impurity of the organic layer330, a surface dipole of the interface between the electron transport layer334and the second electrode349can be regulated according to the organic n-type impurity. Therefore, electrons injected from the second electrode340can be effectively transported to the emitting layer333. For example, the electron transport layer334may be made of C60 (fullerene). The organic n-type impurity may be one or more organic n-type impurities and, as a specific, non-limiting example, may be pyronine B or dicarbocyanine iodide or a combination thereof.

The electron transport layer334may be formed by using the vacuum deposition method, the spin coating method, the cast method, or the LB method. The electron transport layer334may have a thickness of 100 Å to 400 Å, preferably, 150 Å to 250 Å. The electric charge may be out of balance due to an excessive electron transport speed when the thickness of the electron transport layer334is less than 100 Å. On the other hand, the driving voltage may rise when the thickness of the electron transport layer334is greater than 400 Å.

According to the embodiment shown inFIG. 2, an organic layer330-1may be constructed such that the electron transport layer334doped with an n-type impurity and an electron injection layer335are sequentially laminated between the emitting layer333and the second electrode340. The electron injection layer335may be made of Li, Cs, Mg, BaF2, LiF, NaCl, CsF, Li2O, BaO, CaF2, Cs2CO3, Cs2O, CaO, MgF2, MgO, or Liq (8-hydroxy-quinolinato lithium) expressed by Chemical Formula 19. However, the embodiment of the present invention is not limited thereto.

The electron injection layer335may be formed by using the vacuum deposition method, the spin coating method, the cast method, or the LB method. For example, when the vacuum deposition method or the spin coating method is used to deposit the electron injection layer335, deposition can be carried out under the same deposition conditions as the hole injection layer331.

The electron injection layer335may have a thickness of 2 Å to 40 Å. As a specific, non-limiting example, the thickness may be 2 Å to 10 Å. When the thickness of the electron injection layer335is less than 2 Å, electrons may not be effectively injected. When the thickness of the electron injection layer335is greater than 10 Å, the driving voltage may rise.

as According to the embodiment shown inFIG. 3, an organic layer330-2may be constructed such that the electron transport layer334doped with an n-type impurity and an undoped electron transport layer336are sequentially laminated between the emitting layer333and the second electrode340.

According to the embodiment shown inFIG. 4, an organic layer330-3may be constructed such that a first undoped electron transport layer336-1, the electron transport layer334doped with an n-type impurity, and a second undoped electron transport layer336-2are sequentially laminated between the emitting layer333and the second electrode340.

Table 1 shows a comparison result between characteristics of respective Examples wherein the organic light emitting diode includes an electron transport layer doped with organic n-type impurity, in comparison to a Comparison Example wherein the organic light emitting diode does not include an electronic transport layer doped with an organic n-type impurity. The Examples and Comparison Example were tested under the condition that 100 mA/cm2of DC was supplied, and the emitting layer of the organic light emitting diode was an Alq3layer. In the Example 1, an electron transport layer was formed between the second electrode and the emitting layer comprising C60 doped with 15 wt % of pyronine B. In Example 2, an electron transport layer was formed between the second electrode and the emitting layer comprising C60 doped with 15 wt % of dicarbocyanine iodide. In Example 3, an electron transport layer comprising a layer of C60 doped with 15 wt % of pyronine B and a layer of C60 were sequentially laminated between the second electrode and the emitting layer. In the case 4, an electron transport layer comprising layer of C60 doped with 15 wt % of dicarbocyanine iodide and a layer of C60 were sequentially laminated between the second electrode and the emitting layer.

Referring to Table 1, when the organic light emitting diode included the electron transport layer doped with an organic n-type impurity, the brightness characteristic was similar to that of the comparison example, while a lower driving voltage and a higher light efficiency were obtained in comparison with the comparison example.

Now, an organic light emitting display having the organic light emitting diode L1according the embodiment ofFIG. 1will be described with reference toFIG. 5. In this embodiment, like reference numerals denote like elements ofFIG. 1, and detailed descriptions thereof will be omitted.

Referring toFIG. 5, a thin film transistor T1is formed on a substrate110as a driving element. Further, the organic light emitting diode L1is formed above the thin film transistor T1with a planarizing layer260interposed therebetween, and is electrically connected to the thin film transistor T1, thereby forming a pixel. Although a particular structure of the thin film transistor T1is shown inFIG. 5and described herein, it is to be understood that the thin film transistor is not limited to this structure and can be any type of thin film transistor known in the art.

The substrate110may be made of an insulation material or a metallic material. As non-limiting examples, the insulation material may be glass or plastic and the metallic material may be stainless steel (SUS).

In the thin film transistor T1, a buffer layer200is formed on the substrate110and an active layer210is formed on the buffer layer200. The active layer210is composed of source and drain regions211and212and a channel region213disposed between the source and drain regions211and212. A gate insulation layer220is formed on the buffer layer200to cover the active layer210. A gate electrode230is formed on the gate insulation layer220above the active layer210. An intermediate insulation layer240is formed on the gate insulation layer220to cover the gate electrode230. Source and drain electrodes251and252are formed on the intermediate insulation layer240such that the source and drain electrodes251and252are electrically connected to the source and drain regions211and212through first contact holes221and241and second contact holes222and242which are provided to the gate insulation layer220and the intermediate insulation layer240.

The buffer layer200prevents impurities contained in the substrate100from diffusing when the active layer210is formed. For example, the buffer layer200may be made of a silicon nitride (SiN) layer or may be formed in a structure in which a SiN layer and a silicon oxide (SiO2) layer are laminated. The gate electrode230may be constructed with a metal layer, for example, selected from a group consisting of an MoW layer, an Al layer, a Cr layer, and an Al/Cr layer. The source and drain electrodes251and252may be constructed with a metal layer, for example, a Ti/Al layer or a Ti/Al/Ti layer.

The first and second electrodes310and340of the organic light emitting diode L1respectively function as pixel electrodes. Further, the first electrode310can be electrically connected to the drain electrode252of the thin film transistor T1through a via hole261formed in the planarizing layer260. The first electrode310is electrically separated from a first electrode (not shown) of an adjacent pixel by a pixel definition layer320. The first electrode310can be in contact with the organic layer330through an opening321included in the pixel definition layer320.

Accordingly, when the organic light emitting display includes the organic light emitting diode L1ofFIG. 1, due to a low driving voltage and a high emission efficiency of the organic light emitting diode L1, it is possible to reduce the power consumption of the organic light emitting display.