WO2000065879A1

WO2000065879A1 - Organic electroluminescence device with high efficiency reflecting element

Info

Publication number: WO2000065879A1
Application number: PCT/US2000/011161
Authority: WO
Inventors: Gregory T. Prando; Richard A. Campos; Kerry O. Tice
Original assignee: Emagin Corporation
Priority date: 1999-04-28
Filing date: 2000-04-27
Publication date: 2000-11-02

Abstract

The present invention is direct to the concept of an electrode for an OLED (20) formed from multiple layers of metal and dielectric materials that can be ordered to produce a highly efficient electrode (22). The layers of the electrode (22) may be stacked such that different portions of the electrode fulfill the separate functionalities of high electrical conductivity, high electrical injection and high optical transmission/reflection.

Description

ORGANIC ELECTROLUMINESCENCE DEVICE WITH HIGH EFFICIENCY REFLECTING ELEMENT

CROSS REFERENCE TO RELATED PATENT APPLICATION

This application relates to and claims priority on provisional application serial number 60/131,475, filed April 28, 1999.

FIELD OF INVENTION

5 The present invention relates to an organic electroluminescence device. In particular, the present invention relates to a layered or stacked electrode for an organic electroluminescence.

BACKGROUND OF THE INVENTION

An organic electroluminescence device or organic light emitting device ("OLED") is 10 a stack of organic thin films which are in physical contact between two electrodes. The basic structure of an OLED 1 is illustrated in Fig. 1. The OLED 1 includes a substrate 10, a first electrode 11 formed on the substrate 10, at least one organic thin film layer 12 formed on the first electrode 11, and a second electrode 13 formed on the at least one organic thin film layer 12. Typically, several organic thin film layers are sandwiched between the electrodes 15 11 and 13. The electrodes 11 and 13 may be optically reflective or transmissive, depending on the desired direction of light exiting from the OLED 1. The OLED 1 may be encapsulated to maintain material and structural integrity.

The first electrode 11 may be formed from indium tin oxide ("ITO") which has high optical transmission, electrical conductivity and high electrical injection into the at least one 20 organic thin film layer 12. An electrode formed from ITO can be made to have 80-90% optical transmission with 10-100% sheet resistances. ITO is also an operationally good positive-carrier for electrical injection into the at least one organic thin film layer 12. When the first electrode 11 is formed from ITO on substrate 10, the OLED 1 is known as a "down emitting" because the optical output passes through the substrate 10 to the viewer. The

">^ second electrode 13 is then formed from a partially reflective material (e.g., molybdenum, ruthenium and vanadium). The second electrode 13 has a thickness of approximately 1 OOOA. In a "down emitting" OLED. the second electrode 13 may be formed from a pair of layers 131 and 132, as shown in Fig. 2. A very thin layer 131 of a dielectric material (e.g.. LiF and SiO₂) is formed on the at least one thin film layer 12. The layer 131 has a thickness of less than lOOA. A thicker layer 132 of aluminum is formed on the thin layer 131. The thicker layer 132 of aluminum has an approximate thickness of 2000A. Although the operation of composite electrode having layers 131 and 132 is not fully understood, the thin layer 131 is thought to assist electron injection into select organic materials of the thin film layer 12. The aluminum layer 132 is believed to provide functional conductivity and reflectivity within the context of a "down emitting" OLED. OBJECTS OF THE INVENTION

It is an object of the present invention to increase the optical output efficiency of an organic electroluminescence device.

It is another object of the present invention to provide an OLED having an electrode having high optical transmission. It is another object of the present invention to provide an OLED having an electrode having high optical reflection.

It is another object of the present invention to provide an OLED having an electrode having high electrical conductivity.

It is another object of the present invention to provide an OLED having a low-loss, highly directional and reflective element as an integral part of a composite electrode element.

It is another object of the present invention to provide an OLED having a low-loss, highly directional and reflective element as an integral part of a composite electrode element that contacts the organic stack of the OLED.

It is another object of the present invention to provide an OLED having omnidirectional reflectors as part of an electrode element to boost performance of the OLED.

It is another object of the present invention to provide an OLED having omnidirectional reflectors as part of an electrode element to boost performance of the OLED by promoting greater optical output through the reduction of optical losses. It is another object of the present invention to provide an OLED having omnidirectional reflectors as part of an electrode element to boost performance of the OLED by promoting greater directionality of the output optical beam.

It is another object of the present invention to provide an OLED having an electrode comprising a layered stack of metallic and/or dielectric materials.

It is another object of the present invention to provide an OLED having an electrode comprising a layered stack of metallic and/or dielectric materials, which separately functionalize the requirements of high optical transmission or reflection, high electrical conductivity, and high electrical injection into the organic stack. SUMMARY OF THE INVENTION

The present invention is directed to the concept of an electrode for an OLED formed from multiple layers of metal and dielectric materials that can be ordered to produce a highly efficient electrode. The layers of the electrode may be stacked such that different portions of the electrode fulfill the separate functionalities of ( 1 ) high electrical conductivity, (2) high electrical injection and (3) high optical transmission/reflection.

The present invention is directed to an OLED having a substrate, a first electrode formed on said substrate, at least one organic thin film layer formed on the first electrode, and a second electrode formed on the at least one organic thin film layer. In accordance with the present invention, at least one of the first and second electrodes includes a plurality of electrode layers. The plurality of electrode layers includes a thin film layer formed at least one of a metal and an oxide, and a multilayer reflector. The thin film layer preferably has a thickness of less than 100A.

The multilayer reflector includes a plurality of layers. The plurality of layers may include at least one metal layer and at least one dielectric material layer. The plurality of layers preferably includes alternating layers of the at least one metal layer and the at least one dielectric material layer. In accordance with one embodiment of the present invention, the first electrode includes the plurality of electrode layers. In accordance with another embodiment of the present invention, the second electrode includes the plurality of electrode layers.

The plurality of electrode layers preferably includes at least one layer formed from a high electrical conductivity material. The plurality of electrode layers preferably includes at least one layer formed from a high electrical injection material. The plurality of electrode layers preferably includes at least one layer formed from a material having a high optical transmission. The plurality of electrode layers preferably includes at least one layer formed from a material having a high optical reflection. The present invention is also directed to an electrode for an OLED, the electrode includes a plurality of electrode layers, wherein the plurality of electrode layers includes a thin film layer formed at least one of a metal and an oxide, and a multilayer reflector. The thin film layer has a thickness of less than 100 A. The multilayer reflector includes a plurality of layers. The plurality of layers includes at least one metal layer and at least one dielectric material layer. The plurality of layers preferably includes alternating layers of the at least one metal layer and the at least one dielectric material layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in conjunction with the following drawings in which like reference numerals designate like elements and wherein: Fig. 1 is a schematic view of a conventional OLED:

Fig. 2 is a schematic view of another conventional OLED;

Fig. 3 is a schematic view of an upwardly emitting OLED according to an embodiment of the present invention; and

Fig. 4 is a schematic view of a downwardly emitting OLED according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to a preferred embodiment of the present invention, an example of which is illustrated in the accompanying drawings. The OLED 20 in accordance with one embodiment of the present invention is illustrated in Fig. 3. The OLED 20 includes a substrate 21. A first electrode 22 is formed on the substrate 21. At least one organic thin film layer 23 is formed on the first electrode 22. A second electrode 24 is formed on the at least one organic thin film layer 23. The OLED 20 is an upwardly emitting OLED. In an upwardly emitting OLED, light is transmitted through the second electrode 24. The substrate 21 is formed from an opaque material (e.g., silicon). The second electrode 24 is formed from a suitable light transmissive material to permit output of the OLED to exit away from the substrate 21 in the direction of the arrows illustrated in Fig. 3. The first electrode 22 is formed from a plurality of layers. A thin film layer 221 is in direct contact with the at least one organic thin film layer 23. The layer 221 has a thickness of less than lOOA. The layer 221 is formed from a material that promotes positive carrier injection into the at least one organic thin film layer 23. The layer 221 is preferably formed from a metal or an oxide. Suitable metals include molybdenum, ruthenium and vanadium. The present invention, however, is not limited to these materials, rather metals exhibiting similar physical properties are considered to be well within the scope of the present invention. The layer 221 may be formed from oxides of molybdenum, ruthenium, and vanadium or other suitable metals. ITO, aluminum-zinc oxide and mixtures thereof are suitable materials for layer 221.

Positioned between the substrate 21 and the thin layer 221 are alternating layers of metals and dielectric materials 222, 223, 224. 225 forming a high-performance, multilayer reflector 220. This reflector layer 220 has ideal reflectivities, omnidirectionality and low loss, in what is known as a "dielectric omnidirectional reflector." This composite reflector is tuned to the wavelength of electroluminescence emission by suitable choices of the alternating metal and dielectric materials. The omnidirectional mirror combines the best properties of each by inhibiting energy losses through optical interference effects in the periodic, alternating structure.

A second embodiment of the present invention depicted a "downwardly emitting" OLED 30 is illustrated in Fig. 4 having a substrate 31. In a "down-emitting" application, the first electrode 32 is of the usual type, e.g., ITO. and the second electrode 34 is reflective. A thin layer 341 is positioned adjacent to the at least one organic layer 33. The layer 341 is a thin, transparent negative-carrier injector having a thickness of less than 1 OOA. The layer 341 is preferably formed from codeposited layer of magnesium and silver. A plurality of alternating layer 342, 343, 344 and 345 forming a high-performance, multilayer reflector 340 are formed on thin layer 341. The multilayer reflector 340 may also serve as a protective layer for the thin metallic injector 341.

While this invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, the preferred embodiments of the invention as set forth herein are intended to be illustrative, not limiting. Various changes may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

What is claimed is:

1. An organic light emitting device comprising: a substrate; a first electrode formed on said substrate; at least one organic thin film layer formed on said first electrode; and a second electrode formed on said at least one organic thin film layer, wherein at least one of said first and second electrodes includes a plurality of electrode layers.

2. The organic light emitting device according to Claim 1 , wherein said plurality of electrode layers comprises: a thin film layer formed of at least one of a metal and an oxide; and a multilayer reflector.

3. The organic light emitting device according to Claim 2, wherein said thin film layer has a thickness of less than 100A.

4. The organic light emitting device according to Claim 2, wherein said multilayer reflector includes a plurality of layers.

5. The organic light emitting device according to Claim 4, wherein said plurality of layers includes at least one metal layer and at least one dielectric material layer.

6. The organic light emitting device according to Claim 5, wherein said plurality of layers includes alternating layers of said at least one metal layer and said at least one dielectric material layer.

7. The organic light emitting device according to Claim 2. wherein said first electrode includes said plurality of electrode layers.

8. The organic light emitting device according to Claim 2, wherein said second electrode includes said plurality of electrode layers.

9. The organic light emitting device according to Claim 1. wherein said plurality of electrode layers includes at least one layer formed from a high electrical conductivity material.

10. The organic light emitting device according to Claim 1. wherein said plurality of electrode layers includes at least one layer formed from a high electrical injection material.

11. The organic light emitting device according to Claim 1. wherein said plurality of electrode layers includes at least one layer formed from a material having a high optical transmission.

12. The organic light emitting device according to Claim 1. wherein said plurality of electrode layers includes at least one layer formed from a material having a high optical reflection.

13. An electrode for an organic light emitting device, said electrode comprising: a plurality of electrode layers, wherein said plurality of electrode layers includes a thin film layer formed at least one of a metal and an oxide, and a multilayer reflector.

14. The electrode according to Claim 13, wherein said thin film layer has a thickness of less than lOOA.

15. The electrode according to Claim 13, wherein said multilayer reflector includes a plurality of layers.

16. The electrode according to Claim 15, wherein said plurality of layers includes at least one metal layer and at least one dielectric material layer.

17. The electrode according to Claim 16, wherein said plurality of layers includes alternating layers of said at least one metal layer and said at least one dielectric material layer.