OLEDs doped with phosphorescent compounds

Details OLEDs doped with phosphorescent compounds OLEDs doped with phosphorescent compounds

1997-12-01

2001-10-16

Yamnitzky, Marie (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C313S506000, C427S066000, C252S301160

Reexamination Certificate

active

06303238

ABSTRACT:

FIELD OF INVENTION
The present invention is directed to organic light emitting devices (OLEDS) comprised of emissive layers that contain a phosphorescent dopant compound.
BACKGROUND OF THE INVENTION
Organic light emitting devices (OLEDs) are comprised of several organic layers in which one of the layers is comprised of an organic material that can be made to electroluminesce by applying a voltage across the device, C. W. Tang et al.,
Appl. Phys. Lett
51, 913 (1987). Certain OLEDs have been shown to have sufficient brightness, range of color and operating lifetimes for use as a practical alternative technology to LCD-based full color flat-panel displays (S. R. Forrest, P. E. Burrows and M. E. Thompson, Laser Focus World, Febraury 1995). Since many of the thin organic films used in such devices are transparent in the visible spectral region, they allow for the realization of a completely new type of display pixel in which red (R), green (G), and blue (B) emitting OLEDs are placed in a vertically stacked geometry to provide a simple fabrication process, a small R-G-B pixel size, and a large fill factor, International Patent Application No. PCT/US95/15790.
A transparent OLED (TOLED), which represents a significant step toward realizing high resolution, independently addressable stacked R-G-B pixels, was reported in International Patent Application No. PCT/US97/02681 in which the TOLED had greater than 71% transparency when turned off and emitted light from both top and bottom device surfaces with high efficiency (approaching 1% quantum efficiency) when the device was turned on. The TOLED used transparent indium tin oxide (ITO) as the hole-injecting electrode and a Mg—Ag-ITO electrode layer for electron-injection. A device was disclosed in which the ITO side of the Mg—Ag-ITO electrode layer was used as a hole-injecting contact for a second, different color-emitting OLED stacked on top of the TOLED. Each layer in the stacked OLED (SOLED) was independently addressable and emitted its own characteristic color. This colored emission could be transmitted through the adjacently stacked, transparent, independently addressable, organic layer or layers, the transparent contacts and the glass substrate, thus allowing the device to emit any color that could be produced by varying the relative output of the red and blue color-emitting layers.
The PCT/US95/15790 application disclosed an integrated SOLED for which both intensity and color could be independently varied and controlled with external power supplies in a color tunable display device. The PCT/US95/15790 application, thus, illustrates a principle for achieving integrated, full color pixels that provide high image resolution, which is made possible by the compact pixel size. Furthermore, relatively low cost fabrication techniques, as compared with prior art methods, may be utilized for making such devices.
Such devices whose structure is based upon the use of layers of organic optoelectronic materials generally rely on a common mechanism leading to optical emission. Typically, this mechanism is based upon the radiative recombination of a trapped charge. Specifically, OLEDs are comprised of at least two thin organic layers separating the anode and cathode of the device. The material of one of these layers is specifically chosen based on the material's ability to transport holes, a “hole transporting layer” (HTL), and the material of the other layer is specifically selected according to its ability to transport electrons, an “electron transporting layer” (ETL). With such a construction, the device can be viewed as a diode with a forward bias when the potential applied to the anode is higher than the potential applied to the cathode. Under these bias conditions, the anode injects holes (positive charge carriers) into the hole transporting layer, while the cathode injects electrons into the electron transporting layer. The portion of the luminescent medium adjacent to the anode thus forms a hole injecting and transporting zone while the portion of the luminescent medium adjacent to the cathode forms an electron injecting and transporting zone. The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, a Frenkel exciton is formed. Recombination of this short-lived state may be visualized as an electron dropping from its conduction potential to a valence band, with relaxation occurring, under certain conditions, preferentially via a photoemissive mechanism. Under this view of the mechanism of operation of typical thin-layer organic devices, the electroluminescent layer comprises a luminescence zone receiving mobile charge carriers (electrons and holes) from each electrode.
The materials that produce the electroluminescent emission are frequently the same materials that function either as the electron transporting layer or as the hole transporting layer. Such devices in which the electron transporting layer or the hole transporting layer also functions as the emissive layer are referred to as having a single heterostructure.
Alternatively, the electroluminescent material may be present in a separate emissive layer between the hole transporting layer and the electron transporting layer in what is referred to as a double heterostructure.
In addition to emissive materials that are present as the predominant component in the charge carrier layer, that is, either in the hole transporting layer or in the electron transporting layer, and that function both as the charge carrier material as well as the emissive material, the emissive material may be present in relatively low concentrations as a dopant in the charge carrier layer. Whenever a dopant is present, the predominant material in the charge carrier layer may be referred to as a host compound or as a receiving compound. Materials that are present as host and dopant are selected so as to have a high level of energy transfer from the host to the dopant material. In addition, these materials need to be capable of producing acceptable electrical properties for the OLED. Furthermore, such host and dopant materials are preferably capable of being incorporated into the OLED using starting materials that can be readily incorporated into the OLED by using convenient fabrication techniques, in particular, by using vacuum-deposition techniques.
It is desirable for OLEDs to be fabricated using materials that provide electroluminescent emission in a relatively narrow band centered near selected spectral regions, which correspond to one of the three primary colors, red, green and blue so that they may be used as a colored layer in an OLED or SOLED. It is also desirable that such compounds be capable of being readily deposited as a thin layer using vacuum deposition techniques so that they may be readily incorporated into an OLED that is prepared entirely from vacuum-deposited organic materials.
Co-pending U.S. Pat. No. 08/774,087, filed Dec. 23, 1996, now U.S. Pat. No. 6,048,630, is directed to OLEDs containing emitting compounds that produce a saturated red emission. The emission layer is comprised of an emitting compound having a chemical structure represented by Formula I:
wherein X is C or N;
R
8
, R
9
and R
10
are each independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, aryl and substituted aryl; wherein R
9
and R
10
may be combined together to form a fused ring;
M
1
is a divalent, trivalent or tetravalent metal; and a, b and c are each 0 or 1;
wherein, when X is C, then a is 1; when X is N, then a is 0; when c is 1, then b is 0; and when b is 1, c is 0.
The examples disclosed in Ser. No. 08/774,087 (now U.S. Pat. No. 6,048,630) included an emissive compound of formula I wherein X=C; R
8
=phenyl;
R
9
=R
10
=H; c=0; and b=1. This compound has the chemical name 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP). OLEDs comprised of the TPP-containing emissive layer produce an emission spectrum comprised of two narrow bands that are center

Affiliated with

Also associated with

Rating

OLEDs doped with phosphorescent compounds does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with OLEDs doped with phosphorescent compounds, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and OLEDs doped with phosphorescent compounds will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2609820