Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-04-14
2001-05-15
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S503000, C313S509000, C257S098000, C445S024000
Reexamination Certificate
active
06232714
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of fabricating stacked organic light emitting devices (SOLEDs), and more particularly to the use of optical cavities to filter the light output of the SOLED so that color saturation and external quantum efficiency are optimized.
BACKGROUND OF THE INVENTION
Organic light emitting devices, which make use of thin film materials which emit light when excited by electric current, are becoming an increasingly popular technology for applications such as flat panel displays. A typical such organic emissive structure is referred to as a double heterostructure (DH) OLED, shown in FIG.
1
A. In this device, a substrate layer of glass
10
is coated by a thin layer of indium-tin-oxide (ITO)
11
. Next, a thin (100-100 Å) organic hole transporting layer (HTL)
12
is deposited on the ITO layer
11
. Deposited on the surface of HTL
12
is a thin (typically, 50 Å-100 Å) emission layer (EL)
13
. The EL
13
provides the recombination site for electrons injected from a 100-1000 Å thick electron transporting layer
14
(ETL) with holes from the HTL
12
. Examples of ETL, EL and HTL materials are disclosed in U.S. Pat. No. 5,294,870, the disclosure of which is incorporated herein by reference.
Often, the EL
13
is doped with a highly fluorescent dye to tune color and increase the electroluminescent efficiency of the OLED. The device as shown in
FIG. 1A
is completed by depositing metal contacts
15
,
16
and top electrode
17
. Contacts
15
and
16
are typically fabricated from indium or Ti/Pt/Au. Electrode
17
is often a dual layer structure consisting of an alloy such as Mg/Ag 17′ directly contacting the organic ETL
14
, and a thick, high work function metal layer
17
″ such as gold (Au) or silver (Ag) on the Mg/Ag. The thick metal 17″ is opaque. When proper bias voltage is applied between a top electrode
17
and contacts
15
and
16
, light emission occurs from emissive layer
13
through the glass substrate
10
. An OLED such as that of
FIG. 1A
typically has, luminescent external quantum efficiencies of from 0.05% to 2% depending on the color of emission and the device structure.
Another known organic emissive structure referred to as a single heterostructure (SH) is shown in FIG.
1
B. The difference between this structure and the DH structure is that multifunctional layer
13
′ serves as both EL and ETL. One limitation of the device of
FIG. 1B
is that the multifunctional layer
13
′ must have good electron transport capability. Otherwise, separate EL and ETL layers should be included as shown for the device of FIG.
1
A.
Yet another known OLED device is shown in
FIG. 1C
, illustrating a typical cross sectional view of a single layer (polymer) OLED. As shown, the device includes a glass substrate
1
coated by a thin ITO layer
3
. A thin organic layer
5
of spin-coated polymer, for example, is formed over ITO layer
3
, and provides all of the functions of the HTL, ETL, and EL layers of the previously described devices. A metal electrode layer
6
is formed over organic layer
5
. The metal is typically Mg, Ca, or other conventionally used low work function metal.
OLEDs can be stacked to form a SOLED, as described in co-pending U.S. Pat. No. 5,707,745, which is incorporated by reference. The SOLED architecture is useful for fabricating low-voltage, color-tunable pixels with independent control of brightness and gray scale, and offers the advantages of minimum pixel size, maximum fill factor and a simple fabrication process. The three-color SOLED illustrates the unique versatility of organic thin film technology to construct highly complex and heterogeneous multilayer systems which are not possible to attain with conventional, inorganic semiconductor technologies. The SOLED pixel architecture can be used in full color flat panel display applications.
SUMMARY OF THE INVENTION
In accordance with the present invention, interference induced by discontinuities in the indices of refraction between different layers of material is used to advantage to cause a multi-layer SOLED structure to act as a filter that can reduce and/or shift the primary color emitted by each light emitting element of the SOLED. For example, if the strongest interference effects in a particular SOLED structure are due to particular electrode layers that reflect a significant proportion of incident light, those electrode layers can define a Fabry-Perot optical cavity that can significantly affect the frequency spectra and intensity of the light emitted by the SOLED. Choosing the size of the optical cavity, the positioning of the light emitting layers within the optical cavity, and which light emitting layers are within the cavity in accordance with the present invention allows color saturation and external quantum efficiency to be optimized with respect to certain predetermined requirements.
The SOLEDs of the present invention can be used in a wide variety of applications, including computer displays, informational displays in vehicles, television monitors, telephones, printers, illuminated signs, large-area screens and billboards.
REFERENCES:
patent: 5707745 (1998-01-01), Forrest et al.
patent: 5757139 (1998-05-01), Forrest et al.
patent: 5917280 (1999-06-01), Barrows et al.
Burrows Paul
Forrest Stephen R.
Shen Zilan
Kenyon & Kenyon
Patel Nimeshkumar D.
Smith Michael J.
The Trustees of Princeton University
LandOfFree
Saturated full color stacked organic light emitting devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Saturated full color stacked organic light emitting devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Saturated full color stacked organic light emitting devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2441758