Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1998-09-01
2002-06-11
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S212000, C428S917000, C313S504000, C313S506000, C257S094000
Reexamination Certificate
active
06403236
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The present invention relates to a polymer light emitting device (hereinafter referred to as an “polymer LED”).
An inorganic electroluminescence device using an inorganic fluorescent substance as a light emitting material (which may hereinafter referred to as an “inorganic EL device”) has been used, for example, as a flat light source for back light or a display device such as a flat panel display and the like, however, high A.C. voltage has been required to emit light.
Recently, Tang et al. manufactured an organic electroluminescence device (hereinafter referred to as an “organic EL device”) having a double-layer structure, comprising a laminate of a light emitting layer made of an organic fluorescent dye and a layer of an organic charge transporting compound generally used, for example, as a photosensitive material for electrophotography (JP-A-59-194393). Since the organic EL device has a feature that emission of light of various colors can be easily obtained, in addition to low-voltage driving and high luminance, in comparison with the inorganic EL device, various attempts for device structure, organic fluorescent dye and organic charge transporting compound have been reported (Jpn. J. Appl. Phys., Vol. 27, page L269 (1988); and J. Appl. Phys., Vol. 65, page 3610 (1989)).
The polymer LED using a polymeric light emitting material, other than the organic EL device mainly using low-molecular weight organic compounds, has been proposed in WO9013148, JP-A-3-244630, Appl. Phys. Lett. Vol.58, page 1982 (1991) and the like. In the Examples of WO9013148, there is disclosed that a poly(p-phenylenevinylene) thin film converted into a conjugated polymer is obtained by forming a film of a soluble precursor on an electrode and then subjecting it to a heat treatment, and a device using the same.
Furthermore, JP-A-3-244630 discloses conjugated polymers having a feature that the conjugated polymers themselves are soluble in solvents and require no heat treatment. Also, in Appl. Phys. Lett. Vol.58, page 1982 (1991), there are described polymeric light emitting materials, which are soluble in solvents, and polymeric LEDs made by using the same.
JP-A-3-273087 discloses a polymer LED formed by laminating a light emitting layer of a polymeric light emitting material and a hole transporting layer of a conjugated polymer. In case of a polymer LED, a device having high light emitting efficiency can also be obtained by providing a laminated structure. However, there has been required an organic EL device having a sufficient long-term stability, wherein a decrease in luminance and an increase in voltage on driving are smaller than those of these devices.
A method of elongating the lifetime of a light emitting device is proposed, for example, in WO94/06157, JP-A-8-231951 and the like, particularly with respect to an organic EL device made by deposition of a low-molecular-weight material. WO94/06157 discloses that, when a small amount of distyrylalylene derivative is added to a light emitting layer or a hole transporting layer, it functions as an charge injection assistant, and the lifetime of the device is elongated. JP-A-8-231951 discloses that a device having a elongated lifetime can be obtained by using a light emitting layer made by adding a condensed polycyclic aromatic compound to a diamine derivative.
On the other hand, regarding the polymer LED, since an organic layer can be easily formed by coating, it is advantageous to increase the area and to reduce the cost compared with the case where a low-molecular-weight material is deposited. It is considered that the mechanical strength of the film is also excellent by virtue of polymer, but elongation of the lifetime is unsatisfactory. That is, an improvement in stability on driving is required in the polymer LED.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a long-life polymer light emitting device having excellent stability on driving.
Under these circumstances, the present inventors have intensively studied. As a result, the present inventors have found that a long-life polymer light emitting device having excellent stability can be obtained without deteriorating the feature such as luminance, light emitting efficiency and the like, by adding a specific organic compound to a charge transporting layer. Thus, the present invention has been accomplished.
That is, the present invention relates to a polymer light emitting device at least having a light emitting layer containing a polymeric fluorescent substance and a charge transporting layer provided adjacent to the light emitting layer between electrodes consisting of a pair of an anode and a cathode, at least one of which electrode is transparent or semitransparent, wherein said polymeric fluorescent substance contains one or more kind of repeating units represented by the following formula (1), the sum of the repeating units being not less than 50% by mol based on the total repeating units, and has a number-average molecular weight of 10
3
to 10
7
in terms of polystyrene
—Ar
1
—CR
1
═CR
2
— (1)
(wherein Ar
1
represents an arylene group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocyclic compound group having 4 to 20 carbon atoms taking part in a conjugated bond; and R
1
and R
2
independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group), and said charge transporting layer contains an organic compound satisfying the following conditions 1 and 2 in an amount of from 1 to 70% by weight
E
OX2
−0.15≦
E
OX1
≦E
OX2
+0.10 (condition 1)
&lgr;
edge2
−30≦&lgr;
edge1
≦&lgr;
edge2
+20 (condition 2)
(wherein E
OX1
and &lgr;
edge1
respectively represent an electrochemically determined oxidation potential and an absorption edge wavelength of an absorption spectrum of said organic compound; E
OX2
and &lgr;
edge2
respectively represent an electrochemically determined oxidation potential and an absorption edge wavelength of an absorption spectrum of said polymeric fluorescent substance used in said light emitting layer; and the unit in the condition 1 is V and the unit in the condition 2 is nm).
DETAILED DESCRIPTION OF THE INVENTION
As the structure of the polymer LED of the present invention, a light emitting layer containing a polymeric fluorescent substance and a charge transporting layer containing the organic compound (A) are laminated.
For example, the structures of the following (a) to (e) are shown.
(a) Anode/Hole transporting layer (Organic compound(A))/Light emitting layer/Cathode
(b) Anode/Hole transporting layer (Organic compound (A))/Light emitting layer/Electron transporting layer/Cathode
(c) Anode/Light emitting layer/Electron transporting layer (Organic compound (A))/Cathode
(d) Anode/Hole transporting layer/Light emitting layer/Electron transporting layer (Organic compound(A))/Cathode
(e) Anode/Hole transporting layer (Organic compound(A))/Light emitting layer/Electron transporting layer (Organic compound(A))/Cathode
In the above, the symbol “/” represents lamination, and “(Organic compound(A))” represents that the organic compound(A) is contained in the layer.
Two or more light emitting layers, hole transporting layers and electron transporting layers may be independently used and, furthermore, a buffer layer may be inserted into any of interfaces in order to improve the adhesion and prevent the interface from the mixing. The order and number of layers to be laminated and the thickness of each layer are not specifically limited, but can be appropriately used considering the light emitting efficiency and the lifetime of the device.
Furthermore, the present invention also includes the case where the organic compound (A) is contained in the charge transporting layer and, at the same time, contained in the light emitting layer in the
Doi Shuji
Noguchi Takanobu
Ohnishi Toshihiro
Garrett Dawn
Kelly Cynthia H.
Sumitomo Chemical Company Limited
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