US20080048561A1

US20080048561A1 - Organic light emitting diode

Info

Publication number: US20080048561A1
Application number: US11/974,628
Authority: US
Inventors: Jia-Shyong Cheng; Chung-Chih Wu; Chih-Jen Yang
Original assignee: Hannstar Display Corp
Current assignee: Hannstar Display Corp
Priority date: 2003-10-22
Filing date: 2007-10-15
Publication date: 2008-02-28
Also published as: TW200515836A; TWI308846B; JP2005129496A; US20050088080A1; US7321196B2

Abstract

An organic light emitting diode is provided. The organic light emitting diode includes a substrate, an anode electrode structure formed on the substrate and including at least a metal layer and a metal oxide layer, an organic layer formed on the anode electrode structure and a cathode electrode structure formed on the organic layer. The metal oxide layer includes an oxide of the metal layer and has a thickness ranged between 1 to 50 nm

Description

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-part of application Ser. No. 10/903,678 filed Jul. 30, 2004, hereby incorporated by reference as it fully set forth herein.

FIELD OF THE INVENTION

The present invention relates to an organic light emitting diode, and more particularly to an electrode structure of an organic light emitting diode.

BACKGROUND OF THE INVENTION

Generally, the organic light emitting diode (OLED) is formed by depositing the organic thin film between the upper metal cathode and the bottom transparent anode. The OLED is manufactured on the transparent substrate, e.g. the glass, and the transparent anode is made of the transparent conductor such as the indium tin oxide (ITO). Please refer to FIG. 1, which is a typical organic light emitting diode with multiple heterogeneous structures. The organic light emitting diode comprises an anode 11, a cathode 17 and a plurality of organic layers including a hole injection layer 12, a hole transport layer 13, an emitting layer 14, an electron transport layer 15, and an electron injection layer 16. Such conventional organic light emitting diode belongs to a type of bottom-emitting OLED. When applying a bias voltage to the layers 12-16 between the anode 11 and the cathode 17, the light emits through the transparent anode 11 and the substrate (not shown). Please refer to FIGS. 2(a) and 2(b). FIG. 2(a) shows the typical materials of the hole transport layer, such as α-naphtylphenylbiphenyl diamine (α-NPD) and 1,1,4,4-tetra phenyl-1,3-butadiene (TPD), and the typical material of the electron transport layer and a green-fluorescence emitting layer, such as tris(8-hydroxyquinolino) aluminum (Alq3). FIG. 2(b) shows the typical materials of the hole injection layer 12, such as polyethylene dioxythiophene: polystyrene sulphonate (PEDOT:PSS) and 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA).
In some OLED applications, such as the one applied on the silicon-chip substrate or other opaque substrate, the OLED is designed to a top-emitting structure. Since the light must emit through the top surface of the top-emitting OLED, the cathode on the top of the OLED would be transparent or translucent. Furthermore, in some other OLED applications, the OLED could be transparent in the top and bottom so that the light could transmit therethrough. Hence, in addition to the transparence of the anode, the cathode on the top of the OLED also could be transparent or translucent.
Moreover, in the most applications of the active matrix OLED displays (AMOLEDs), the light generated from the organic layers is emitted downward via the transparent substrate and the ITO. Nevertheless, the driving circuit of the OLED has to be integrated into each pixel thereof. Accordingly, the area for emitting the generated light is limited to the aperture ratio of the substrate carrying the driving circuit. For this reason, the top-emitting structure might be more preferable for preventing the generated light from being degraded by the covering area of the driving circuit, especially when the driving circuit is more complicated. Specifically, the top-emitting OLED is not only capable of improving the image quality and the properties of the display but also capable of increasing the design flexibility of the AMOLED for the layout the driving circuit. Therefore, with the top-emitting OLED, it is possible to design an AMOLED with the driving circuit for better functions (e.g. resolution) and properties.
At the present day, there are two major methods for manufacturing the transparent or translucent cathode of the top-emitting OLED. The first one is that the top transparent cathode is formed by sputtering the transparent ITO or other transparent metal oxide conductors with the electron injection layers, while the second one is that the top transparent cathode is formed by the thin metal layer having a thickness less than a few tens of nanometers.
The first method is disclosed in U.S. Pat. No. 6,548,956, No. 6,469,437, No. 6,420,031, No. 6,264,805, No. 5,986,401, No. 5,981,306, No. 5,703,436, No. 6,140,763 and No. 5,776,623. Nevertheless, because the deposited organic layer is easily damaged during the sputtering process for the cathode of the OLED, the sputtering process for the ITO or other transparent metal oxide conductors on the organic layer is relatively difficult to be well controlled. Besides, since the power of the sputtering should be as low as possible so as to prevent the thin film deposited underneath from being damaged, the processing time for the cathode of the OLED is prolonged. Meanwhile, the conductivities of most transparent metal oxide conductors are substantially less than those of the metals since the transparent metal oxide conductors have higher resistance than the metals. Accordingly, the traditional schemes for producing the cathode of the OLED still have some problems sought to be overcome.
On the other hand, the abovementioned second method is to utilize the thin metal layer having a thickness less than a few tens of nanometers as the translucent cathode. The thin metal layer not only has better conductivity, but also is more easily formed on other organic layers. However, the major problem in using the thin metal layer as the translucent cathode is that the transparency of such translucent cathode is lower. For example, the transmittance of the Ag layer with a thickness of 20 nm is only 30%. The transmittance of the Al layer with a thickness of 20 nm is even lower. The transmittance of the layer composed of the Ca layer of 12 nm and the Mg layer of 12 nm is only 40-50%.
There exist some known schemes for improving the transmittance of the cathode formed by the thin metal layer having a thickness less than a few tens of nanometers, such as those technical features disclosed in the respective U.S. Pat. No. 5,739,545, No. 6,501,217 and No. 5,714,838. Typically, the conventional cathode structure is formed by a thin metal layer having high activity and low work function, such as Ca, Mg, Sr, Li or the stacks thereof, which is also incorporated with a transparent dielectric or a large band gap semiconductor, such as ZnSe, ZnS or GaN upon the thin metal layer for improving the transmittance thereof. All the materials used in the disclosed patents are preferably deposited by thermal evaporation so as to simplify the manufacturing processes and improve the compatibility of the process. However, the major problem of such cathode structure is that the utilized metal material, such as Ca, Mg, Sr or Li, has higher activity and reactivity, which are very disadvantageous for the environmental stabilization of the components.
In view of the above, it is clear that the transparent cathode formed by a thin metal layer incorporated with a transparent dielectric or a large band gap semiconductor, not only has a better transmittance but also could be fabricated with a process compatible with the known process. Nevertheless, it still has somewhat disadvantages that the metal used in the thin metal layer belongs to the unstable metal with high activity, which might result in the environmental stabilization issues of the cathode structure. Further, some transparent dielectric materials with high refractive-index value might have problems in being manufactured by the thermal evaporation deposition.
On the other hand, no matter what kinds of conductive materials the anode of the OLED is made of, there usually exists the hole injection problem in the anode. This is because the work function of the conductive material of the anode is different from the ionization potential (IP) of the organic opto-electronic materials, and such difference exist therebetween would cause a disadvantageous effect on the hole injection from the anode to the organic layer.
Based on the above, it is preferable to develop a new OLED having an anode structure with an appropriate work function for improving the hole injection of the anode into the organic hole transport layer. Furthermore, as mentioned previously, it is also preferable to develop a new OLED with the translucent cathode structure having thereon a metal with lower activity and transparent dielectric material formed by the thermal evaporation deposition.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present invention, an organic light emitting diode is provided. The organic light emitting diode includes a substrate, an anode electrode structure formed on the substrate and including at least a metal layer and a metal oxide layer, an organic layer formed on the anode electrode structure, and a cathode electrode structure formed on the organic layer.
Preferably, the metal oxide layer includes an oxide of the metal layer and has a thickness ranged between 1 to 50 nm.
Preferably, the cathode electrode structure includes a thin metal layer.
Preferably, the thin metal layer is one selected from a group consisting of layers of Al, Ag, Cr, and Mo, stack layers thereof and a layer of a combination thereof.
Preferably, the metal layer is selected from one of a group consisting of transition metals and Group 13 metals.
Preferably, the metal oxide layer is disposed between the metal layer and the organic layer.
Preferably, the metal oxide layer includes a silver oxide layer.
Preferably, the thickness of the metal oxide layer is ranged between 1.5 and 25 nm.
Preferably, the thin metal layer has a thickness less than 40 nm.
Preferably, the cathode electrode structure includes an electron injection layer.
Preferably, the electron injection layer includes an Al layer.
Preferably, the Al layer has a thickness less than 4 nm.
Preferably, the electron injection layer further includes an alkali-salt layer.
Preferably, the alkali-salt layer has a thickness ranged between 0.1 and 4 nm.
Preferably, the alkali-salt layer is one selected from a group consisting of layers of LiF, LiO2, and NaCl, stack layers thereof and a layer of a combination thereof.
Preferably, the metal oxide layer is one selected from a group consisting of layers of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, zinc oxide, aluminum zinc oxide (AZO), and tellurium oxide, stack layers thereof and a layer of a combination thereof.
Preferably, the anode electrode structure further includes a conductive polymer layer formed on the metal oxide layer.
Preferably, the conductive polymer layer is one selected from a group consisting of layers of polyethylene dioxythiophene/polystyrene sulphonate (PEDOT/PSS), 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), and polyaniline (PANI), stack layers thereof and a layer of a combination thereof.
In accordance with a second aspect of the present invention, a further organic light emitting diode is provided. The organic light emitting diode includes a substrate, an anode electrode structure formed on the substrate and including a metal layer, a metal oxide layer formed on the metal layer, an organic layer formed on the anode electrode structure, and a cathode electrode structure formed on the organic layer.
Preferably, the metal oxide layer includes a metal component selected from one of a group consisting of transition metals and Group 13 metals and an oxide of the metal layer has a thickness ranged between 1 to 50 nm;
Preferably, the thickness of the oxide of the metal layer is ranged between 1.5 and 25 nm.
In accordance with a third aspect of the present invention, a further organic light emitting diode is provided. The organic light emitting diode includes a substrate, an anode electrode structure formed on the substrate, an organic layer formed on the anode electrode structure, and an cathode electrode structure having at least one transparent dielectric layer with a refraction index greater than 2.0 within a wavelength of visible light, wherein the anode electrode structure includes a metal layer and a silver oxide layer disposed on the metal layer, and the silver oxide layer has a thickness ranged between 1 to 50 nm.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a diagram showing the structure of the bottom-emitting OLED according to the prior art;
FIG. 2(a) is a diagram showing the structures of α-NPD and TPD which are the materials of the hole transport layer and the structure of Alq3 which is the material of the green-fluorescence emitting layer and the electron transport layer according to the prior art;
FIG. 2(b) is a diagram showing the structures of PEDOT:PSS and m-MTDATA, the conducting polymers, which are the materials of the hole injection layer according to the prior art;
FIG. 3 is a diagram showing the OLED according to a preferred embodiment of the present invention;
FIG. 4 is a diagram showing the transparent cathode according to a preferred embodiment of the present invention;
FIG. 5 is a diagram showing the OLED having the transparent cathode according to a further preferred embodiment of the present invention;
FIG. 6 is a diagram showing the electric characteristic curves of the OLED according to a further preferred embodiment of the present invention;
FIG. 7 is a diagram showing the spectrum measurements with different angles of the OLED according to a further preferred embodiment of the present invention, wherein the peak values have been normalized;
FIG. 8 is a diagram showing the electric characteristic curves of the OLED according to a further preferred embodiment of the present invention;
FIG. 9 is a diagram showing the electric characteristic curves of the OLED according to a further preferred embodiment of the present invention;
FIG. 10 is a diagram showing the voltage-current characteristic curves of the OLED using the Ag anode without AgO_x(▪) and with AgO_x(●) according to a preferred embodiment of the present invention;
FIG. 11 is a diagram showing the luminance efficiency-current characteristic curves of the OLED using the Ag anode without AgO_x(▪) and with AgO_x(●) according to a preferred embodiment of the present invention; and
FIG. 12 is a diagram showing the voltage-current characteristic curves of the OLED using the Al anode without AgO_x(▪) and with AgO_x(●) according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will now be described more specifically with reference to the following embodiments. It is to be noted that the following descriptions of preferred embodiments of this invention are presented herein for purpose of illustration and description only; it is not intended to be exhaustive or to be limited to the precise form disclosed.
Please refer to FIG. 3, which is a diagram showing the OLED having the transparent cathode according to a preferred embodiment of the present invention. The OLED includes a substrate 31, an anode 32, an organic layer 33 and a transparent cathode 34. The anode 32 is deposited on the substrate 31. The organic layer 33 is deposited on the anode 32. The transparent cathode 34 is deposited on the organic layer 33. The anode 32 is made of a metal layer 321 and a metal oxide layer 322 having a thickness ranged between 1 and 50 nm and deposited on the metal layer 321. Preferably, the thickness of the metal oxide layer 322 could be designed to be ranged between 1.5 and 25 nm. In addition, preferably, the metal oxide layer 322 could include a metal component selected from a group consisting of transition metals and Group 13 metals. Take the Ag₂O for example, because the Ag₂O has the band gap of 1.3 eV, the ionization potential (IP) of 5.3 eV which is 1 eV higher than the work function of Ag, and the properties of the p-type semiconductor with the Fermi level ranging from 4.8 to 5.1 eV, which match with the energy level of the material of the hole transport layer of the OLED, the luminance of the OLED and the hole injection would be substantially enhanced under the same voltage operation. And the anode with metal oxide, Ag₂O, retains a high reflectance of 82%-91% over the visible range. Moreover, the metal oxide layer 322 could be formed by chemical vapor deposition (CVD), sputtering deposition (including reactive sputtering deposition), thermal evaporation, electron-beam evaporation, oxygen plasma oxidation, oxygen environment oxidation, UV-ozone treatment oxidation, wet chemical oxidation or electrochemical oxidation.
The aforementioned UV-ozone treatment oxidation is to convert the oxygen molecules in the atmosphere into the ozone and the oxygen atoms by utilizing the UV light wavelength of 254 nm generated by a low pressure quartz mercury vapor lamp. Then the metal oxide layer would be formed by the thin metal film exposed to the condition. For example:
2 Ag_(s)+O_3(g)→Ag₂O_(s)+O_2(g).
The substrate 31 of the OLED according to the present invention could be a transparent substrate such as the glass, the quartz and the plastic. The substrate 31 of the OLED according to the present invention also could be an opaque substrate such as the silicon chip and the GaAs chip. In a further embodiment, when the substrate 31 is designed to be an opaque substrate, the metal oxide layer 322 also could be an opaque layer with a corresponding opaque layer material.
The metal layer 321 of the OLED according to the present invention could be one selected from a group with rather high reflectivity consisting of layers of the transition metals and Group 13 metals, such as Ag, Au, Al, Cu, Mo, Ti, Pt, Ir, Ni and Cr, stack layers thereof and a layer of a combination thereof.
The organic layer 33 of the OLED according to the present invention could be a single layer structure with the functions of the charge transport and the luminance. Further, the organic layer 33 of the OLED according to the present invention could also be multiple layers which could be formed by one of the following methods: (1) depositing the hole transport layer and the electron transport layer (as the luminance layer) in sequence on top of the electrode; (2) depositing the hole transport layer (as the luminance layer) and the electron transport layer in sequence on top of the electrode; and (3) depositing the hole transport layer, the luminance layer and the electron transport layer in sequence of top of the electrode. Other possible structures and the materials of the organic layer of the OLED could be found in the prior references and patents.
The transparent cathode 34 of the OLED according to the present invention could be made of one metal selected from a group with rather high reflectivity consisting of Mg, Ca, Al, Ba, Li, Be, Sr, Cr, Mo, Ag, and Au, the stack thereof and a combination thereof. The transparent cathode 34 of the OLED according to the present invention also could be the metal material collocating with the electron injection layer which is typically the alkali-salt layer. For example, the transparent cathode 34 is Al, which could be collocated with the electron injection layer made of LiF, LiO₂, NaCl, stack layers thereof or a layer of a combination thereof. The cathode 34 of the OLED according to the present invention also could be a transparent electrode which is made of one material selected from a group consisting of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, zinc oxide, aluminum zinc oxide (AZO), and tellurium oxide, a stack thereof and a combination thereof.
Please refer to FIG. 4, a diagram showing the transparent cathode according to a preferred embodiment of the present invention. The transparent cathode 40 includes a LiF layer 411, an Al layer 412, an Ag layer 42 and a TeO₂layer 43. The LiF layer 411 has a thickness ranged between 0.1 and 4 nm. The Al layer 412 is deposited on the LiF layer 411 and has a thickness ranged between 0.1 and 4 nm. The Ag layer 42 is deposited on the Al layer 412 and has a thickness ranged between 5 and 40 nm. And the TeO₂layer 43 is deposited on the Ag layer 42. The LiF layer 411 is collocated with the Al layer 412 as the electron injecting layer for increasing the electron injecting from the cathode to the organic layer underneath (not shown). The TeO₂layer 43 is a transparent dielectric with a relatively higher refraction index ranged between 2.0 and 2.5. Besides, the TeO₂layer 43 could be deposited by thermal evaporation so as to simplify the manufacturing processes and improve the compliance of the processes. Moreover, the TeO₂layer 43 deposited on the LiF layer 411/the Al layer 412/the Ag layer 413 could be used to increase the light transmission of the transparent cathode 40. In other words, since the TeO₂layer 43 with higher refraction index than that of the typical dielectric could be deposited on the low activity Ag layer 42 by thermal evaporation, the transparent cathode 40 with better light transmission could be applied to the top-emitting OLED.
Please refer to FIG. 5, which is a diagram showing the OLED having the transparent cathode according to a further preferred embodiment of the present invention. The OLED 50 includes a substrate 51, an anode 52, an organic layer 53, a LiF layer 411, an Al layer 412, an Ag layer 42 and a TeO₂layer 43. The anode 52 is deposited on the substrate 51. The organic layer 53 is deposited on the anode 52. The LiF layer 411 is deposited on the organic layer 53 and has a thickness ranged between 0.1 and 4 nm. The Al layer 412 is deposited on the LiF layer 411 and has a thickness ranged between 0.1 and 4 nm. The Ag layer 42 is deposited on the Al layer 412 and has a thickness ranged between 5 and 40 nm. And the TeO₂layer 43 is deposited on the Ag layer 42. Please refer to FIGS. 4 and 5, the LiF layer 411 is collocated with the Al layer 412 as the electron injecting layer for improving the electron injecting from the cathode 40 to organic layer 53 underneath. The TeO₂layer 43 is a transparent dielectric with a relatively higher refraction index ranged between 2.0 and 2.5. Besides, the TeO₂layer 43 could be deposited by thermal evaporation. The light transmission of the transparent cathode 40 could be increased by depositing the TeO₂layer 43 on the LiF layer 411/the Al layer 412/the Ag layer 42.
The anode 52 could be a conductive transparent metal oxide layer. The conductive transparent metal oxide layer is one selected from a group consisting of layers of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, zinc oxide, aluminum zinc oxide (AZO), tellurium oxide.
In addition, the anode 52 could be a stack layers or a layer of a combination of the conductive polymer layer deposited on the aforementioned conductive transparent metal oxide layer. The conductive polymer layer is one selected from a group consisting of layers of polyethylene dioxythiophene/polystyrene sulphonate (PEDOT/PSS), 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), and polyaniline (PANI), stack layers thereof and a layer of a combination thereof.
Further, the anode 52 could also be the stack layers or a layer of a combination of a metal oxide layer deposited on a conductive metal layer. The conductive metal layer is one selected from a group with rather high reflectivity consisting of layers of transition metals and Group 13 metals, such as, Ag, Au, Al, Cu, Mo, Ti, Pt, Ir, Ni and Cr, stack layers thereof and a layer of a combination thereof. The metal oxide layer is one selected from a group consisting of layers of the oxide of the aforementioned metal, stack layers thereof and a layer of a combination thereof.
The metal oxide layer, such as silver oxide, mentioned above has a thickness of ranged between 1 and 50 nm. And preferably, the thickness of the metal oxide layer could be designed to be ranged between 1.5 and 25 nm. The metal oxide layer could be formed by one selected from a group consisting of chemical vapor deposition (CVD), sputtering deposition (including reactive sputtering deposition), thermal evaporation, electron-beam evaporation, oxygen plasma oxidation, oxygen environment oxidation, UV-ozone treatment oxidation, wet chemical oxidation and electrochemical oxidation.
Furthermore, the anode 52 could also be the stack layers or a layer of a combination of a conductive transparent metal oxide layer deposited on a conductive metal layer. The conductive metal layer is made of one selected from a group consisting of layers of transition metals and Group 13 metals, such as, Ag, Au, Al, Cu, Mo, Ti, Pt, Ir, Ni and Cr, stack layers thereof and a layer of a combination thereof. The conductive transparent metal oxide layer is one selected from a group consisting of layers of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, zinc oxide, aluminum zinc oxide (AZO), and tellurium oxide, stack layers thereof and a layer of a combination thereof.
The anode 52 could also be the stack layers or a layer of a combination of a conductive polymer layer deposited on the conductive metal layer. The conductive metal layer is one selected from a group consisting of layers of transition metals and Group 13 metals, such as, Ag, Au, Al, Cu, Mo, Ti, Pt, Ir, Ni and Cr, stack layers thereof and a layer of a combination thereof. The conductive polymer layer is one selected from a group consisting of layers of polyethylene dioxythiophene/polystyrene sulphonate (PEDOT/PSS), 4,4′,4″-tris(3-methylphenylphenylamino) triphenylamine (m-MTDATA), and polyaniline (PANI), stack layers thereof and a layer of a combination thereof.
The anode 52 could also be the stack layers or a layer of a combination of a conductive metal layer, a metal oxide layer and a conductive polymer layer deposited sequentially. The conductive metal layer is one selected from a group consisting of layers of transition metals and Group 13 metals, such as, Ag, Au, Al, Cu, Mo, Ti, Pt, Ir, Ni and Cr, stack layers thereof and a layer of a combination thereof. The metal oxide layer is one selected from a group consisting of layers of the oxide of the aforementioned metal, stack layers thereof and a layer of a combination thereof. For example, the conductive metal layer could be an Ag layer, and the metal oxide layer could be directly designed and formed as an AgO layer. The conductive polymer layer is one selected from a group consisting of layers of polyethylene dioxythiophene/polystyrene sulphonate (PEDOT/PSS), 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), and polyaniline (PANI), stack layers thereof and a layer of a mixture thereof.
The organic layer 53 could be the single layer structure with the functions of the charge transport and the luminance. Further, the organic layer 53 could also be multiple layers, which could be formed by one of the following methods: (1) depositing the hole transport layer and the electron transport layer (as the luminance layer) in sequence on top of the electrode; (2) depositing the hole transport layer (as the luminance layer) and the electron transport layer in sequence on top of the electrode; and (3) depositing the hole transport layer, the luminance layer and the electron transport layer in sequence on top of the electrode.
According to a further preferred embodiment of the present invention, an OLED could be made by a glass substrate, an Ag layer (80 nm), an ITO layer (5.8 nm), an α-NPD layer (50 nm), an Alq3 layer (60 nm), a LiF layer (0.5 nm), an Al layer (0.6 nm), an Ag layer (15 nm) and a TeO₂layer (40 nm).
The Ag layer on top of the glass substrate and the ITO deposited thereon could be used as the anode. The α-NPD layer could be the organic hole transport layer. The Alq3 layer could be the organic electron transport layer and the green-fluorescence emitting layer. The LiF layer (0.5 nm)/the Al layer (0.6 nm)/the Ag layer (15 nm)/the TeO₂layer (40 nm) could be the transparent cathode. The anode including the Ag layer and the ITO layer deposited thereon is used as the reflection anode. The light of the OLED is emitted from the top transparent cathode.
FIG. 6 shows the electric characteristic curves of the aforementioned OLED. FIG. 7 shows an EL spectra with different view angles of the aforementioned OLED, wherein the peak values have been normalized. It can be seen that even the view angle reaches 60° off the surface normal, there is still no obvious changes in the spectrum and the hue is still green which is the original hue of the Alq3.
While the aforementioned OLED is tested, it is found that the lateral conductivity of the extremely thin ITO layer is very low. Therefore, even though the ITO is deposited completely without patterning, there is still no crosstalk occurred between two adjacent OLEDs. In other words, it is possible to omit the patterning process for the ITO layer by applying such structure to the AMOLED. Hence, the ITO injection layer could be collocated with any metal layers.
According to a further preferred embodiment of the present invention, a further OLED could be made by a glass substrate, an Al layer (150 nm), an ITO layer (30 nm), a PEDOT:PSS layer (25 nm), an α-NPD layer (30 nm), an Alq3 layer (70 nm), a LiF layer (0.5 nm), an Al layer (0.6 nm), an Ag layer (15 nm), and a TeO₂(32 nm) layer.
The Al layer on top of the glass substrate, the ITO layer deposited thereon and the PEDOT:PSS layer could be used as the anode. The α-NPD layer could be the organic hole transport layer. The Alq3 layer could be the organic electron transport layer and the green-fluorescence emitting layer. The LiF layer (0.5 nm)/the Al layer (0.6 nm)/the Ag layer (15 nm)/the TeO₂layer (32 nm) could be used as the transparent cathode. The anode including the Al layer and the ITO layer deposited thereon is the reflection anode. The light of the OLED is emitted from the top transparent cathode. The electric characteristic curves of the aforementioned OLED is shown in FIG. 8.
According to a further preferred embodiment of the present invention, a further OLED could be made by a glass substrate, an Ag layer (150 nm), a PEDOT:PSS layer (20 nm), an α-NPD layer (30 nm), an Alq3 layer (70 nm), a LiF layer (0.5 nm), an Al layer (0.6 nm), an Ag layer (15 nm) and a TeO₂layer (32 nm).
The Ag layer on top of the glass substrate and the PEDOT:PSS layer mounted thereon could be used as the anode. The α-NPD layer could be the organic hole transport layer. The Alq3 layer could be the organic electron transport layer and the green-fluorescence emitting layer. The LiF layer (0.5 nm)/the Al layer (0.6 nm)/the Ag layer (15 nm)/the TeO₂layer (32 nm) could be the transparent cathode. The anode including the Ag layer and the PEDOT:PSS layer deposited thereon is the reflection anode. The light of the OLED is emitted from the top transparent cathode. The electric characteristic curves of the aforementioned OLED is shown in FIG. 9.
Please refer to FIG. 10, which is a diagram showing the voltage-current characteristic curves of the OLED 1 (without a AgO_xlayer) and the OLED 2 (with a AgO_xlayer) according to the preferred embodiments of the present application, in which:
OLED 1 is formed by a glass substrate, an Ag layer (80 nm), an m-MTDATA layer (30 nm), an α-NPD layer (20 nm), an Alq3 layer (50 nm), a LiF layer (0.5 nm), an Al layer (1 nm), an Ag layer (20 nm), and a TeO₂layer (40 nm); and
OLED 2 is formed by a glass substrate, an Ag layer (80 nm), an AgO_xlayer, an m-MTDATA layer (30 nm), an α-NPD layer (20 nm), an Alq3 layer (50 nm), a LiF layer (0.5 nm), an Al layer (1 nm), an Ag layer (20 nm), and a TeO₂layer (40 nm).
The Ag layer on top of the glass substrate could be the metal layer of the electrode in both OLEDs. The only difference between the two OLEDs is whether the OLED has the AgO_xlayer or not. The AgO_xlayer in OLED 2 is formed by an oxidation of the Ag layer through the UV-ozone treatment oxidation for 1 minute. The OLED 1 is not treated with the UV-ozone treatment. Other organic materials such as the m-MTDATA layer and the α-NPD layer are used as the organic hole transport layer and The Alq3 layer could be the organic electron transport layer and the green-fluorescence emitting layer. The sequences and the thicknesses of these organic layers in two OLEDs are the same. The LiF layer (0.5 nm)/the Al layer (1 nm)/the Ag layer (20 nm)/the TeO₂layer (40 nm) could be used as the transparent cathode. The metal layer, the Ag layer, of the anode is the reflection anode. The lights of the two OLEDs are both emitted from the top transparent cathode. Under the same voltage, the current increase of the OLED 2 is more than that of the OLED 1. That is, the AgO_xlayer capable of improving the efficiency of the hole injecting to the OLED. The comparison of the luminance efficiency characteristic curves of the two OLEDs is shown in FIG. 11. Under the same current density, the luminance efficiency of the OLED 2 is more than that of the OLED 1. As the result, the OLED with the hole injection layer of the AgO_xlayer has a better luminance efficiency.
Furthermore, please refer to FIG. 12, which is the diagram showing the voltage-current characteristic curves of the OLED 1 (without a AgO_xlayer) and the OLED 2 (with a AgO_xlayer) according to the further preferred embodiments of the present application, in which:
OLED 1 is formed by a silicon substrate, an Al layer (100 nm), an m-MTDATA layer (30 nm), an α-NPD layer (20 nm), an Alq3 layer (50 nm), a LiF layer (0.5 nm), an Al layer (1 nm), an Ag layer (20 nm) and a TeO₂layer (40 nm); and
OLED 2 is formed by a silicon substrate, an Al layer (100 nm), an AgO_xlayer, an m-MTDATA layer (30 nm), an α-NPD layer (20 nm), an Alq3 layer (50 nm), a LiF layer (0.5 nm), an Al layer (1 nm), an Ag layer (20 nm) and a TeO₂layer (40 nm).
The Al layers on top of the glass substrates could be the metal layers of the electrode structures in both two OLEDs. The only difference between the two OLEDs is whether the OLED has the AgO_xlayer or not. The AgO_xlayer in OLED 2 is formed by oxidizing the thin Ag film of 5 nm through the UV-ozone treatment oxidation for 1 minute. The OLED 1 is not treated with the UV-ozone treatment. Other organic materials such as m-MTDATA and α-NPD are the organic hole transport layers and the Alq3 layer could be the organic electron transport layer and the green-fluorescence emitting layer. The sequence and the thicknesses of the organic layers in two OLEDs are the same. The LiF layer (0.5 nm)/the Al layer (1 nm)/the Ag layer (20 nm)/the TeO₂layer (40 nm) could be used as the transparent cathode. The metal layer, the thick Al film, of the electrode as the anode is the reflection anode. The lights of the two OLEDs are both emitted from the top transparent cathode. Under the same voltage, the current of the OLED 2 is more than that of the OLED 1. That is, the AgO_xlayer helpful to improve the efficiency of the hole injecting to the OLED.
While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the invention need not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures. Therefore, the above description and illustration should not be taken as limiting the scope of the present invention which is defined by the appended claims.

Claims

1. An organic light emitting diode, comprising:

a substrate;

an anode electrode structure formed on the substrate and comprising at least a metal layer and a metal oxide layer, wherein the metal oxide layer comprises an oxide of the metal layer and has a thickness ranged between 1 to 50 nm;

an organic layer formed on the anode electrode structure; and

a cathode electrode structure formed on the organic layer.

2. The organic light emitting diode according to claim 1 wherein the cathode electrode structure comprises a thin metal layer.

3. The organic light emitting diode according to claim 2 wherein the thin metal layer is one selected from a group consisting of layers of Al, Ag, Cr, and Mo, stack layers thereof and a layer of a combination thereof.

4. The organic light emitting diode according to claim 1, wherein the metal layer is selected from one of a group consisting of transition metals and Group 13 metals.

5. The organic light emitting diode according to claim 1, wherein the metal oxide layer is disposed between the metal layer and the organic layer.

6. The organic light emitting diode according to claim 1, wherein the metal oxide layer comprises a silver oxide layer.

7. The organic light emitting diode according to claim 1, wherein the thickness of the metal oxide layer is ranged between 1.5 and 25 nm.

8. The organic light emitting diode according to claim 2 wherein the thin metal layer has a thickness less than 40 nm.

9. The organic light emitting diode according to claim 1 wherein the cathode electrode structure comprises an electron injection layer.

10. The organic light emitting diode according to claim 9 wherein the electron injection layer comprises an Al layer.

11. The organic light emitting diode according to claim 10 wherein the Al layer has a thickness less than 4 nm.

12. The organic light emitting diode according to claim 10 wherein the electron injection layer further comprises an alkali-salt layer.

13. The organic light emitting diode according to claim 12 wherein the alkali-salt layer has a thickness between 0.1 and 4 nm.

14. The organic light emitting diode according to claim 12 wherein the alkali-salt layer is one selected from a group consisting of layers of LiF, LiO2, and NaCl, stack layers thereof and a layer of a combination thereof.

15. The organic light emitting diode according to claim 1 wherein the metal oxide layer is one selected from a group consisting of layers of indium tin oxide (ITO), indium zinc oxide (IZO), indium oxide, tin oxide, zinc oxide, aluminum zinc oxide (AZO), and tellurium oxide, stack layers thereof and a layer of a combination thereof.

16. The organic light emitting diode according to claim 1 wherein the anode electrode structure further comprises a conductive polymer layer formed on the metal oxide layer.

17. The organic light emitting diode according to claim 16 wherein the conductive polymer layer is one selected from a group consisting of layers of polyethylene dioxythiophene/polystyrene sulphonate (PEDOT/PSS), 4,4′,4″-tris(3-methylphenylphenylamino)triphenylamine (m-MTDATA), and polyaniline (PANI), stack layers thereof and a layer of a combination thereof.

18. An organic light emitting diode, comprising:

a substrate;

an anode electrode structure formed on the substrate and comprising a metal layer;

a metal oxide layer formed on the metal layer, wherein the metal oxide layer comprises a metal component selected from one of a group consisting of transition metals and Group 13 metals and an oxide of the metal layer has a thickness ranged between 1 to 50 nm;

an organic layer formed on the metal oxide layer; and

a cathode electrode structure formed on said organic layer.

19. The organic light emitting diode according to claim 18, wherein the thickness of the oxide of the metal layer is ranged between 1.5 and 25 nm.

20. An organic light emitting diode, comprising:

a substrate;

an anode electrode structure formed on the substrate;

an organic layer formed on the anode electrode structure;

a cathode electrode structure having at least one transparent dielectric layer with a refraction index greater than 2.0 within a wavelength of visible light,

wherein the anode electrode structure comprises a metal layer and a silver oxide layer disposed on the metal layer, and the silver oxide layer has a thickness ranged between 1 to 50 nm.