Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2002-02-28
2003-07-15
Clinger, James (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C257S094000
Reexamination Certificate
active
06593689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an organic light-emitting device. More particularly, the invention relates to an organic light-emitting device having a light-emitting element comprising a pair of electrodes and an organic light-emitting material layer sandwiched by the electrodes. This device is applicable to various types of display device.
2. Description of the Related Art
Electro-Luminescence (EL) elements are one of the types of light-emitting elements designed for display devices EL elements are divided into two types, “organic EL elements” using an organic material layer as the light-emitting layer and “inorganic EL elements” using an inorganic material layer as the light-emitting layer.
The basic configuration of organic EL elements comprises an anode, a cathode, and a thin, layer-shaped organic EL structure made of an organic light-emitting (i.e., electro-luminescent, EL) compound or compounds sandwiched by the anode and the cathode. If a proper voltage is applied across the anode and cathode, holes are injected from the anode into the organic EL structure and at the same time, electrons are injected from the cathode into the same structure, resulting in recombination of the holes and electrons. Due to the energy generated by the recombination, the molecules of the material that forms the EL layer are excited. These molecules thus excited will be returned to their energetic ground states, in other words, deactivated. During this deactivation process, a light-emitting (i.e., EL) phenomenon will occur. The above-described organic EL elements utilize this phenomenon.
The organic EL structure comprises an organic layer termed the “light-emitting layer” that emits light using the recombination of holes and electrons. If necessary, an organic layer termed the “hole-transportation layer” and/or an organic layer termed the “electron-transportation layer” are additionally provided. The “hole-transportation layer” has a property that injection of holes is easy while transportation of electrons is difficult. The “electron-transportation layer” has a property that injection of electron is easy while transportation of holes is difficult.
Thus, if the El structure comprises only the light-emitting layer, it has a single-layer structure. If the EL structure comprises at least one of the hole-transportation layer and the electron-transportation layer along with the light-emitting layer, it has a multi-layer (i.e., two- or three-layer) structure.
In recent years, organic EL elements have been vigorously researched and they are on the way to put them into practice. These prior-art organic EL elements have the basic configuration comprising a transparent electrode (i.e., a hole-injection electrode, anode), a thin hole-injection material layer formed on the transparent electrode, a light-emitting layer formed on the hole-injection material layer, and a metal electrode (i.e., an electron-injection electrode, cathode). The transparent electrode for hole injection (i.e., anode) is made of an indium sin oxide (ITO) or she like. The hole-injection material layer is made of triphenyl diamine (TPD) or the like, which is formed by evaporation. The light-emitting layer is made of a fluorescent material, such as an aluminum quinolinol complex (Alq
3
). The metal electrode for electron injection (i.e., cathode) is made of a metal having a low work function, such as AgMg.
These prior-art organic EL elements afford us very high brightness of several hundreds cd/m
2
to several hundreds thousands cd/m
2
as a voltage of approximately 10 V. Therefore, they have been drawing our attention because of their application fields, such as lighting, light sources, display devices for so-called OA (office automation) instruments, household electrical appliances, automobiles, motorcycles, and airplanes.
For example, the prior-art EL elements designed for these application fields have the configuration that the organic layers (e.g., the light-emitting or EL layer) are sandwiched by the scan electrodes (i.e., common line electrodes) serving as the electron-injection electrodes and the data electrodes (i.e., segment line electrodes) serving as the hole-injection (transparent) electrodes. The organic layers and the scan and data electrodes are located on a transparent substrate, such as a glass plate.
The display devices including the light-emitting elements are divided into two groups, the “matrix type” and the “segment type”. With the “matrix type”, the light-emitting elements, which are arranged in the form of a matrix, are driven by the scan and data electrodes to form a dot matrix on the display screen. Desired information, such as images and/or characters, is displayed on the screen as a set of the dots. On the other hand, with the “segment type”, a set of display segments is prepared in advance. These segments are separately formed in the screen, each of which has a predetermined shape and size. Desired information is displayed on the screen as a combination of the segments.
With the segment-type display devices, each of the display segments may be driven separately from each other. Unlike this, with the matrix-type display devices, the dynamic drive method has been adopted in such a way that the scan lines and the data lines are driven in the time-division manner.
The configuration of the light-emitting device comprising the light-emitting element is divided into two types, i.e., the “substrate-surface-emission” type and the layer-surface-emission” type.
With the “substrate-surface-emission” type, the four-layer structure made of the transparent substrate, the transparent electrode (i.e., the hole-injection electrode or anode), the light-emitting layer, and the metal electrode (i.e., the electron-injection electrode or cathode) formed in this order is used. The light generated in the light-emitting layer is emitted to the outside from the surface of the substrate by way of the transparent electrode and the transparent substrate. An example of this type is disclosed in the paper, Applied Physics Letters, Vol. 51, No. 12, Sep. 21, 1987, pp. 913-915.
On the other hand, with the “layer-surface-emission” type, the four-layer structure made of the substrate, the metal electrode (i.e., the electron-injection electrode or cathode), the light-emitting layer, and the transparent electrode (i.e., the hole-injection electrode or anode) formed in this order is used. The light generated in the light-emitting layer is emitted to the outside from the opposite surface of the transparent electrode to the substrate by way of the transparent electrode. An example of this type is disclosed in the paper, Applied Physics Letters, Vol. 65, No. 21, Nov. 21, 1994, pp. 2636-2638.
A typical configuration of the prior-art organic light-emitting devices of this type is shown in FIG.
1
.
The light-emitting device of
FIG. 1
comprises a light-emitting element
100
formed on a transparent substrate
105
. The substrate
105
is formed by a transparent plate. A current-supplying element
102
is connected to the element
100
to supply an electric current to the element
100
. A switching element
101
is connected to the element
102
.
Typically, although not shown here, the light-emitting element
100
has a five-layer structure made of a transparent electrode (i.e., a hole-injection electrode or anode), a hole-injection layer, a light-emitting layer, an electron-transportation layer, and a metal electrode (i.e., an electron-injection layer or cathode) stacked on the substrate
105
in this order. The transparent electrode is the nearest to the substrate
105
. As each of the current-supplying element
102
and the switching element
101
, a Thin-Film Transistor (TFT) of the Metal-Oxide-Semiconductor (MOS) type is typically used.
With the prior-art light-emitting device of
FIG. 1
, the light emitted from the light-emitting layer of the light-emitting element
100
travels vertically through the substrate
105
to its surface
106
. Since the refractive index of the substrate
105
Fukuchi Takashi
Hayashi Kazuhiko
Oda Atsushi
Tsuboi Shinnzo
Clinger James
Hayes & Soloway P.C.
NEC Corporation
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