Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2001-08-09
2004-02-03
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C349S189000
Reexamination Certificate
active
06685524
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART
The present invention relates to an organic electroluminescence device used as a light-emitting device for flat panel displays, projection displays, printers, etc., and a process for producing the organic electroluminescence device.
In flat panel display, a liquid crystal device has been widely used. Particularly, a so-called active matrix-type liquid crystal device (e.g., TFT (thin film transistor)-type liquid crystal device) wherein each pixel is provided with a switching or active element such as TFT has been used predominantly in the field of flat panel display.
In such an active matrix-type liquid crystal device, however, a nematic liquid crystal is generally used as a liquid crystal material and is accompanied with a longer response time (slower response speed) to an applied electric field, e.g., on the order of several ten milliseconds, thus being unsuitable for high-speed image display such as motion picture display. Further, the liquid crystal device is accompanied with a large dependence of viewing angle since a birefringence state of liquid crystal changes depending on a viewing direction.
In order to solve the above-mentioned problems, self-emission type devices for the flat panel display, such as a plasma emission device, a field emission device, and an electroluminescence device (hereinafter, referred to as “EL device”) have attracted notice in recent years.
Of these self-emission type devices, the EL device is classified into an organic EL device and an inorganic EL device.
The inorganic EL device comprises a thin film EL device using an inorganic semiconductor (e.g., ZnS) driven by AC voltage application. The inorganic EL device is excellent in gradational characteristic and luminance but is accompanied with a problem such that the device is required to employ an AC drive voltage of the order of several hundred volts.
On the other hand, with respect to the organic EL device, T. W. Tang et al. have substituted in 1987 that it is possible to realize a high-luminance luminescence with low power consumption by utilizing a lamination structure comprising a film of fluorescent metal chelate complex and a film of diamine-based molecules.
The organic EL device is a self-emission device of carrier injection-type wherein electrons and holes are re-combined in a luminescence layer to cause luminescence (emission of light), as shown in FIG.
1
.
FIG. 1
is a schematic sectional view of an embodiment of an ordinary organic EL device. Referring to
FIG. 1
, the organic EL device comprises a cathode
11
, an anode
14
, and an organic (compound) layer
16
, including a luminescence layer
12
and a hole transport layer
13
, disposed between the cathode
11
and the anode
14
.
The organic EL device shown in
FIG. 1
includes the organic layer
16
between the cathode
11
comprising a metal electrode and the anode
14
comprising a transparent electrode for emitting light therefrom. The respective layers (luminescence layer
12
and hole transport layer
13
) constituting the organic layer
16
may generally have a thickness of the order of several hundred Å. Examples of a material for the metal electrode (cathode)
11
may generally include those having smaller work functions, such as aluminum, aluminum-lithium alloy and magnesium-silver alloy. Further, as a material for the transparent electrode (anode)
14
, it is possible to use an electroconductive material having a lager work function, such as ITO (indium tin oxide).
The organic layer
16
disposed between the cathode
11
and the anode
14
may have a three-layer structure including an electron transport layer
15
, a luminescence layer
12
and a hole transport layer
13
as shown in
FIG. 2
, in addition to the lamination structure shown in FIG.
1
.
The hole transport layer
13
has a function of efficiently injecting holes from the anode
14
to the luminescence layer
12
. The electron transport layer
15
has a function of efficiently injecting electrons from the cathode
11
to the luminescence layer
12
. Further, the hole transport layer
13
and the electron transport layer
15
also have functions of confining electrons and holes in the luminescence layer
12
, respectively (i.e., carrier blocking functions), thus enhancing a luminescence efficiency.
With respect to carrier transport layers such as the hole transport layer
13
and the electron transport layer
15
, it is important to improve charge (carrier) transport performances particularly a carrier mobility.
Generally, organic compounds in amorphous state have a carrier mobility of the order of 10
−5
cm
2
/V.sec, thus resulting in an insufficient (carrier) transport performance. Accordingly, if the carrier can be increased, it becomes possible to inject a larger amount of carriers into the luminescence layer, thus enhancing a resultant luminescence efficiency. At the same time, if a higher mobility can be achieved, it is possible to make a generally thin carrier transport layer (several hundred A) thicker (about 1 &mgr;m), thus resulting in not only prevention of an occurrence of short circuit but also improvement in productivity.
For this reason, materials (compounds) for the carrier transport layers have been extensively developed in order to accomplish a high-efficiency organic electroluminescence device.
In such circumstances, some proposals have been made for achieving a higher (carrier) mobility by imparting a mesomorphism to an organic compound constituting a carrier transport layer (film). Generally, an organic layer (film) used in the organic EL device is in an amorphous state, thus having no regularity in molecular alignment (orientation). On the other hand, with respect to a liquid crystalline organic compound (or mesomorphic organic compound) exhibiting a certain order or regularity in molecular alignment or orientation, higher mobility materials have been found. Specifically, Haarer et al having confirmed that long-chain triphenylene compounds being a typical discotic liquid crystal exhibited a higher hole mobility of 10
−1
cm
2
/V.sec (Nature (1994), Vol. 371, pp. 141-). Haarer et al have also reported that a larger hole mobility was given by a higher degree of order in molecular alignment as a result of study on a relationship between a degree of order in molecular alignment and a hole mobility with respect to a series of triphenylene-based discotic liquid crystals in (discotic) columnar phase (Nature (1996), Vol. 8, pp. 815-). Further, Hanna et al have reported that a rod-shaped liquid crystal having a phenylnaphthalene skeleton exhibited a mobility of 10
−2
cm
2
/V.sec in its smectic E phase and that the liquid crystal had a high-speed bipolar carrier conductivity as to electrons and holes (Appl. Phys. Lett. (1998), Vol. 73, [25], pp. 3733-).
As described above, there is a possibility that molecular alignment advantageous to carrier transport is controlled by a spontaneous alignment (orientation) of a liquid crystalline organic compound, thus leading to a possibility that an excellent carrier transport material is realized.
Further, it has been found by our research group that it was possible to remarkably improve not only a carrier transport performance but also a carrier injection performance from an electrode based on a spontaneous alignment characteristic of a liquid crystalline organic compound as a result of study on the liquid crystalline carrier transport material (U.S. patent application Ser. No. 09/656,942), filed Sep. 7, 2000, corr. to Japanese Laid-Open Patent Application (JP-A) No. 2001-167888 and European Patent Application (EP-A) No. 1083613A2). Accordingly, it is possible to improve performances of organic EL device by using the liquid crystalline carrier transport layer as a carrier injection layer in combination with appropriate transport layer and luminescence layer.
The liquid crystalline organic compound also has an advantage in production process for an organic EL device. Generally, when an organic film is formed, vacuum vapor deposition
Furugori Manabu
Kamatani Jun
Miura Seishi
Moriyama Takashi
Okada Shinjiro
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