Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-05-04
2003-12-16
Yamnitzky, Marie (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C428S332000, C313S504000, C313S506000
Reexamination Certificate
active
06663985
ABSTRACT:
BACKGROUND OF THE INVENTION
1.Field of the Invention
The present invention relates to a display, and more particularly, to an organic electroluminescent (EL) device.
2. Background of the Related Art
Organic EL devices, also called organic light emitting diodes (LEDs), are becoming very popular because of their possible application to flat panel displays (FPDs). Organic EL devices are extremely thin, matrix-addressable and operable at a relatively low voltage, typically less than 15 volts. Furthermore, they have additional features suitable for next generation FPDs such as, among other things, little dependence on viewing angle and good device-formability on flexible substrates. Organic LEDs differ fundamentally from conventional inorganic LEDs. For Example, the charge transfer in inorganic LEDs is band-like in nature and the electron-hole recombination results in the interband emission of light; while organic films are generally characterized by low-mobility activated hopping transport, and the emission is excitonic. Furthermore, organic EL devices are substantially different from conventional inorganic EL devices in other respects, notably in that in that organic EL devices are operable at low DC voltages.
Referring to
FIG. 1
, a typical organic EL device is shown with a first electrode
2
formed on a transparent substrate
1
, a hole injecting layer (HIL)
3
and a hole transporting layer (HTL)
4
formed on the first electrode
2
, a luminescent layer
5
formed on the HTL
4
, an electron transporting layer (ETL)
6
and an electron injecting layer (EIL)
7
formed on the luminescent layer
5
, and a second electrode
8
formed on the EIL
7
. Any one or more of HIL
3
, HTL
4
, ETL
6
and EIL
7
may be omitted, depending on the particular device structure adopted.
Electrons and holes injected into the luminescent layer through the second electrode
8
and the first electrode
2
, respectively, recombine to decay radiatively. For most organic EL devices, the charge injection barrier is higher for electrons than for holes. It is well known that the electron injection barrier may be lowered by employing a low work function material for the second electrode
8
. However, low work function materials are chemically reactive, which makes it difficult to use such materials for electrodes. Accordingly, such materials are often used as a second electrode after being alloyed with one of more stable materials, as seen in the examples of Mg:Ag and Al:Li. However, such alloyed second electrodes are still less stable, more costly to form, and more difficult to deposit in a uniform film as compared to aluminum.
An even more serious problem often encountered with an alloyed second electrode of Mg:Ag or Al:Li is the frequent occurrence of cross talk or current leakage between pixels, which may be attributed to the diffusion of Mg or Li ions across organic layers of the device. This problem can be greatly alleviated if one selects aluminum as a second electrode material. However, in the case of aluminum there is a need to improve its poor electron injecting capability. The electron injecting capability of a high work function second electrode, such as aluminum, can be significantly enhanced by inserting a very thin layer (typically 0.3 nm ~1.0 nm) of an electrically insulating material such as LiF, MgF
2
or Li
2
O, inserted either between an aluminum electrode and the luminescent layer, or between the aluminum electrode and the ETL(see, for example, IEEE Transactions on Electronic Devices, Vol. 44, No. 8, p 1245-1248(1997), the contents of which are incorporated herein in their entirety).
Li
2
O is a particularly interesting material, in this regard, in that it is an electrically insulating material with a very low work function. The work function of alkali metals themselves is very low, and it becomes even lower when oxidized: for example, work function decreases from 2.1 eV for Cs to about 1 eV for Cs
2
O. Various alkali metal compounds have reportedly been used to form an insulating buffer layer for the purpose of lowering the electron injecting barrier: e.g., Li
2
O, LiBO
2
, NaCl, KCl, K
2
SiO
3
, RbCl, and Cs
2
O to name a few. Despite this improvement, the introduction of the insulating buffer layer poses a challenging new problem, namely, deterioration of adhesion between an EL multilayer and aluminum, with consequent reduction of life time of the device. Experimental results reveal evidence of poor adhesion either at the buffer layer/aluminum interface or at the EL multilayer/buffer layer interface. This situation is not unexpected, given the different characteristics of materials involved. In summary, organic EL devices of the related art have at least two basic drawbacks, namely, poor adhesion and short life time.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an organic electroluminescent device that substantially obviates one or more of the problems, limitations and/or disadvantages of the related art.
An object of the present invention is to provide an organic EL device with a long life time and have high efficiency.
To achieve these and other advantages, and in accordance with the present invention as embodied and broadly described herein, the organic electroluminescent device comprises at least one organic EL multilayer disposed between a first electrode and a second electrode, and a layer I, disposed between the organic EL multilayer and the second electrode, including at least one first material from the group consisting of compounds of chemical formula I:
where:
each of R
1
to R
4
is independently hydrogen, an alkyl or alkoxy group having from 1 to 5 carbon atoms, aryl, aryloxy or a halogen, or at least one among pairs of adjacent substituents of R
1
through R
4
may form an five or six- numbered conjugated cyclic ring which may includes carbon, nitrogen, or sulfur; and,
A each independently denotes hydrogen, an alkyl group having from 1 to 5 carbon atoms, or aryl.
Herein, the term the organic EL multilayer may encompass a plurality of layers comprising a luminescent layer and typically one or more of the HIL, HTL, ETL, and EIL.
In a preferred form of the invention, said each of R
1
to R
4
is independently hydrogen, an alkyl and alkoxy group having from 1 to 5 carbon atoms, phenoxy, phenyl, naphthyl, fluorine, chlorine, or bromine, and said A each independently denotes methyl, ethyl, phenyl, or hydrogen.
In a highly preferred form of the invention, said R
1
is an alkyl and alkoxy group having from 1 to 5 carbon atoms, phenoxy, or phenyl, and said each of R
2
to R
4
and A is independently hydrogen.
In addition, the above-mentioned organic electroluminescent device may further comprise a layer II including at least one second material selected from the group consisting of an alkali metal, an alkaline earth metal, and a compound thereof, which may be disposed between the layer I and the second electrode. Preferably, said second electrode may comprise aluminum. Also, said layer II may comprise Li
2
O. Said layer I may have a thickness of from about 0.5 nm to about 50 nm, and said layer II may have a thickness of from about 0.2 nm to about 3 nm.
According to another aspect of this invention, there is provided a means to improve the life time of an organic EL device, as well as the electron injecting capability, by inserting, instead of a dual layer of the layer I and the layer II, a mixed layer comprising a mixture of the components of layer I and layer II, wherein the mixed layer is inserted between the organic EL multilayer and the second electrode. The mixed layer is formed by the co-deposition of (1) at least one first material selected from the group consisting of compounds of chemical formula I and (2) at least one second material selected from the group consisting of an alkali metal, an alkaline earth metal, and a compound thereof. The ratio between th
Kim Myung Seop
Kim Sung Tae
Oh Hyoung Yun
Yoon Jong Geun
Fleshner & Kim LLP
LG Electronics Inc.
Yamnitzky Marie
LandOfFree
Organic electroluminescent device with improved long-term... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Organic electroluminescent device with improved long-term..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organic electroluminescent device with improved long-term... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3184035