Organic electronic devices having conducting self-doped...

Details Organic electronic devices having conducting self-doped... Organic electronic devices having conducting self-doped...

1999-09-03

2003-08-26

Patel, Ashok (Department: 2879)

Electric lamp and discharge devices

With luminescent solid or liquid material

Solid-state type

C313S509000, C313S512000, C428S917000

Reexamination Certificate

active

06611096

ABSTRACT:

TECHNICAL FIELD
This invention relates to organic electronic devices and in particular buffer layers for organic light emitting diodes (OLEDs).
BACKGROUND
Organic electronic devices are articles that include layers of organic materials, at least one of which can conduct an electric current. An example of an organic electronic device is an organic light emitting diode (OLED). OLEDs, sometimes referred to as lamps, are desirable for use in electronic media because of their thin profile, low weight, and low driving voltage, i.e., less than about 20 volts. OLEDs have potential use in applications such as backlighting of graphics, pixelated displays, and large emissive graphics.
OLEDs typically consist of an organic light emitter layer and additional organic charge transport layers on both sides of the emitter, all of which are sandwiched between two electrodes: a cathode and an anode. The charge transport layers comprise an electron transporting layer and a hole transporting layer. Charge carriers, i.e., electrons and holes, are injected into the electron and hole transporting layers from the cathode and anode, respectively. Electrons are negatively charged atomic particles and holes are vacant electron energy states that behave as though they are positively charged particles. The charge carriers migrate to the emitter layer, where they combine to emit light.
FIG. 1
illustrates a type of organic light emitting diode. The diode comprises a substrate
12
, a first electrode (anode)
14
, a hole transporting layer
16
, a light emitting layer
18
, an electron transporting layer
20
, and a second electrode (cathode)
22
.
Substrate
12
may be transparent or semi-transparent and may comprise, e.g., glass, or transparent plastics such as polyolefins, polyethersulfones, polycarbonates, polyesters, and polyarylates.
Anode
14
is electrically conductive and may be optically transparent or semi-transparent. Suitable materials for this layer include indium oxide, indium-tin oxide (ITO), zinc oxide, vanadium oxide, zinc-tin oxide, gold, copper, silver, and combinations thereof.
An optional hole injecting layer (not shown) may accept holes from anode
14
and transmit them to hole transporting layer
16
. Suitable materials for this layer include porphyrinic compounds, e.g., copper phthalocyanine (CuPc) and zinc phthalocyanine.
Hole transporting layer
16
facilitates the movement of holes from anode layer
14
to emitter layer
18
. Suitable materials for this layer include, e.g., aromatic tertiary amine materials described in U.S. Pat. Nos. 5,374,489 and 5,756,224, (both incorporated by reference) such as 4,4′,4″-tri(N-phenothiazinyl) triphenylamine (TPTTA), 4,4′,4″-tri(N-phenoxazinyl) triphenylamine (TPOTA), N,N′-diphenyl-N,N′-bis(3-methylphenyl)[1,1′-biphenyl]-4,4′-diamine (TPD), and polyvinyl carbazole.
Emitter layer
18
comprises an organic material capable of accommodating both holes and-electrons. In emitter layer
18
, the holes and electrons combine to produce light. Suitable materials for this layer include, e.g., tris(8-hydroxyquinolinato)aluminum (AlQ). The emission of light of different colors may be achieved by the use of different emitters and dopants in the emitter layer as described in the art (see C. H. Chen, J. Shi, and C. W. Tang “Recent Developments in Molecular Organic Electroluminescent Materials”,
Macromolecular Symposia
1997 125, 1-48).
Electron transporting layer
20
facilitates the movement of electrons from cathode
22
to emitter layer
18
. Suitable materials for this layer include, e.g., AlQ, bis(10-hydroxy-benzo(h)quinolinato) beryllium, bis(2-(2-hydroxy-phenyl)-benzolthiazolato) zinc and combinations thereof.
An optional electron injecting layer (not shown) may accept electrons from the cathode
22
and transmit them to the emitter layer
18
. Suitable materials for this layer include metal fluorides such as LiF, CsF, as well as SiO
2
, Al
2
O
3
, copper phthalocyanine (CuPc), and alkaline metal compounds comprising at least one of Li, Rb, Cs, Na, and K such as alkaline metal oxides, alkaline metal salts, e.g., Li
2
O, Cs
2
O, and LiAlO
2
.
Cathode
22
provides electrons. It may be transparent. Suitable materials for this layer include, e.g., Mg, Ca, Ag, Al, alloys of Ca and Mg, and ITO.
Polymer OLEDs may be made wherein a single layer of poly(phenylenevinylene) (PPV) or poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) functions as layers
16
,
18
, and
20
.
Illustrative examples of known OEL device constructions would include molecularly doped polymer devices where charge carrying and/or emitting species are dispersed in-a polymer matrix (see J. Kido, “Organic Electroluminescent devices Based on Polymeric Materials,”
Trends in Polymer Science
, 1994, 2, 350-355), conjugated polymer devices where layers of polymers such as poly(phenylenevinylene) (PPV) act as the charge carrying and emitting species (see J. J. M. Halls, D. R. Baigent, F. Cacialli, N. C. Greenham, R. H. Friend, S. C. Moratti, and A. B. Holmes, “Light-emitting and Photoconductive Diodes Fabricated with Conjugated Polymers,”
Thin Solid Films
, 1996, 276, 13-20), vapor deposited small molecule heterostructure devices (see U.S. Pat. No. 5,061,569, incorporated by reference, and C. H. Chen, J. Shi, and C. W. Tang, “Recent Developments in Molecular Organic Electroluminescent Materials,”
Macromolecular Symposia
, 1997, 125, 1-48), light emitting electrochemical cells (see Q. Pei, Y. Yang, G. Yu, C. Zhang, and A. J. Heeger, “Polymer Light-Emitting Electrochemical Cells: In Situ Formation of a Light-Emitting p-n Junction,”
Journal of the American Chemical Society
, 1996, 118, 3922-3929), and vertically stacked organic light-emitting diodes capable of emitting light of multiple wavelengths (see U.S. Pat. No. 5,707,745, incorporated by reference and Z. Shen, P. E. Burrows, V. Bulovic, S. R. Forrest, and M. E. Thompson “Three-Color, Tunable, Organic Light-Emitting Devices,”
Science
, 1997, 276, 2009-2011).
SUMMARY OF INVENTION
The present invention relates to adding a buffer layer, comprising a self-doped polymer, adjacent to an electrode layer in an organic electronic device. The invention further relates to adding a buffer layer, comprising an intrinsically conducting polymer having no mobile counterions, adjacent to an electrode layer in a small molecule, molecularly doped polymer, or conjugated polymer organic light emitting diode. For example, a buffer layer may be added between the anode layer and hole transporting layer of an organic electronic device to increase performance reliability. A buffer layer could also be added between a substrate and cathode layer.
When the buffer layer of the present invention is used in an organic electronic device such as an organic light emitting diode (OLED), the benefits to performance reliability include reducing or eliminating performance failures such as electrical shorts and non-radiative regions (dark spots). Typical performance failures are described in Antoniadas, H., et al., “Failure Modes in Vapor-Deposited Organic LEDs,”
Macromol. Symp
., 125, 59-67 (1997). The performance reliability of OLEDs can be influenced by a number of factors. For example, defects in, particles on, and general variations in the morphology at the surface of the materials comprising the substrate and electrode layers can cause or exacerbate performance failures that can occur in OLEDs. Particles or defects on the surface of the substrate or electrode layer may prevent the electrode surface from being coated uniformly during the deposition process. This can cause shadowed regions close to the particle or defect. Shadowed areas provide pathways for water, oxygen, and other detrimental agents to come into contact with and degrade the various lamp layers. This degradation can lead to dark spots which can grow into larger and larger non-emissive regions. This degradation can lead to immediate device failure due to electrical shorting or slower, indirect failure caused by interaction of

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