Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-11-27
2004-07-06
Garrett, Dawn L. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S917000, C427S066000, C313S502000, C313S504000, C313S506000
Reexamination Certificate
active
06759145
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an organic electroluminescent (EL) device (also known as OELD) and a method for fabricating the same, and more particularly, to a white light emitting organic electroluminescent device able to directly emit continuous full color light containing three different frequency bands and a method for fabricating such an organic electroluminescent device easily and with high precision. This invention can effectively simplify the fabrication procedure and improve the luminescence efficiency.
2. Description of the Prior Art
The organic electroluminescent device, upon which C. W. Tang and S. A. Van Slyke (Eastman Kodak Company, Rochester, N.Y.) have made efforts since 1987 to form hetero-structures by employing aluminum trisoxine [a.k.a., tris(8-quinolinol)aluminum] by vacuum evaporation, has attracted tremendous attention due to its advantages over other display panels. These advantages include self-luminescence, large visual angle, short response time, compact size, light weight, reduced dimension in thickness, high brightness, low power consumption, simple fabrication, and the ability for light emitting in a full color range. Therefore, such an organic electroluminescent device is increasingly required to replace the currently used white light sources such as fluorescent lamps and light bulbs so as to save energy, and the technologies thereon have widely been studied in the industry all over the world.
Please refer to
FIG. 1
, which is a cross-sectional view showing the structure of an organic EL device disclosed in U.S. Pat. No. 4,769,292, issued Sep. 6, 1988, filed Oct. 14, 1987 by Van Slyke et al (Eastman Kodak Company, Rochester, N.Y.), entitled “Electroluminescent device with modified thin film luminescent zone.” The organic EL device
10
comprises in sequence: a transparent substrate
11
, light transmissive anode
13
formed of tin oxide or indium tin oxide (ITO) by evaporation, an organic hole injecting and transporting zone
15
, a luminescent zone
17
, and a cathode
19
. The luminescent zone
17
is formed by a thin film comprised of an organic host material capable of sustaining hole and electron injection and a fluorescent material (not shown) capable of emitting light in response to hole-electron recombination. When an external voltage is applied to the device
10
, the anode
13
injects holes (positive charge carriers) into the luminescent medium
17
while the cathode
19
injects electrons into the luminescent medium
17
. The portion of the luminescent medium
17
adjacent the anode
13
thus forms a hole injecting and transporting zone
15
. The injected holes and electrons each migrate toward the oppositely charged electrode. This results in hole-electron recombination within the organic luminescent medium
17
, which leads to energy released as light according to the chosen fluorescent material.
The fore-mentioned prior art organic EL device has advantages in good quality and enduring lifetime. However, the structure employed can only emit monochromatic lights according to various chosen fluorescent materials, and fail to achieve the objects of emitting white light or continuous full color light.
Please refer to
FIG. 2
, which is a schematic band diagram showing the structure of an organic EL device disclosed in U.S. Pat. No. 5,668,438, issued Sep. 16, 1997, filed Jun. 6, 1996 and U.S. Pat. No. 5,886,464, issued Mar. 23, 1999, filed Apr. 18, 1997 by Shi et al (Motorola, Inc., Schaumburg, Ill.), both entitled “Organic electroluminescent device with emission from hole transporting layer.” In the EL structure, an anode
22
is formed of tin oxide or indium tin oxide (ITO), an organic hole transporting layer
23
is formed on the anode
22
, an organic electron transporting layer
24
is formed on the hole transporting layer
23
, and a cathode
25
is formed on the electron transporting layer
24
. The materials for the hole and electron transporting layers
23
and
24
are so selected as to satisfy the following inequality:
(
E
C1
−E
C2
)<(
E
V1
−E
V2
)
where E
C1
and E
V1
respectively represent a conduction band level and a valence band level of the material selected for the hole transporting layer
23
; and E
C2
and E
V2
respectively represent a conduction band level and a valence band level of the material selected for the electron transporting layer
24
.
The inequality ensures that the energy barrier for holes to be injected into the valence band of electron transporting layer
24
from the valence band of hole transporting layer
23
is greater than that for electrons to be injected into the conduction band of the hole transporting layer
23
from the conduction band of electron transporting layer
24
. In other words, the number of electrons to be injected from the electron transporting layer
24
into the hole transporting layer
23
is much larger than the number of holes to be injected from the hole transporting layer
23
into the electron transporting layer
24
. Therefore, electrons and holes recombine in the part of hole transporting layer
23
close to the interface of electron transporting layer
24
and hole transporting layer
13
, where light emission occurs. Moreover, in order to facilitate holes to be injected into the hole transporting layer
23
from the anode
22
, the EL structure further provides a hole injection layer interposed between the anode
22
and the hole transporting layer
23
.
Although the fore-mentioned prior art organic EL device has high electroluminescence efficiency due to light emission from the hole transporting layer
23
. However, the structure employed can only emit monochromatic lights according to various chosen fluorescent materials, and fail to achieve the objects of emitting white light or continuous full color light.
In recent years, there are several methods that have been investigated and developed by the industry to realize an organic EL device capable of emitting white light or full color light, including:
1. Color conversion: In this method, a monochromatic light passes through a color conversion material composed of different color conversion layers and is then resolved and converted into light with different colors, e.g. three primary colors, such as red, blue, and green so that an organic EL device capable of emitting white light or full color light can be obtained. However, this method also suffers from a number of problems. First, most of the available color conversion materials are not satisfactory in color purity and luminescence efficiency. Secondly, the background light (such as blue light and UV light) may also be absorbed by the color conversion layers, which often leads to poor contrast and defective pixel quality. And thirdly, the color conversion process is performed by a two-wavelength approach; therefore, chromatic aberration may occur.
2. Color filter: In this method, white light is used as the back-lighting source of the organic EL material. It is useful to achieve full color light when accompanied by LCD color filters. However, the key problem of this method is how to obtain a reliable white light.
3. Three independent colors (RBG): In this method, three primary colors red (R), green (G) and blue (B) are independently demonstrated to realize a full color display or a white light source. However, since the three colors are independently demonstrated, RBG pixels require different driving voltages. A multicolor organic light emitting device thus formed is disclosed in U.S. Pat. No. 5,703,436, issued Dec. 30, 1997, filed Mar. 6, 1996 by Forrest et al (Princeton University, Princeton, N.J.), entitled “Transparent contacts for organic devices.” It suffers from complicated fabrication process and larger size. In addition, in such a device, high precision is critically required for the RBG pixels. As shown in
FIG. 3
, which is a 3-dimensional view showing the structure of an organic EL device disclosed in U.S. Pat. No. 5,952,037, issued Sep. 14, 1999, filed May 8,
Chuang Feng-Ju
Lin Ming-Der
Lin San Bao
Garrett Dawn L.
Opto Tech Corporation
Rosenberg , Klein & Lee
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