Organic electroluminescent element

Details Organic electroluminescent element Organic electroluminescent element

2000-07-11

2002-07-09

Kelly, Cynthia H. (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C428S704000, C313S504000, C313S506000

Reexamination Certificate

active

06416887

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an organic electroluminescence element (hereinafter referred to as an organic EL element), and more particularly relates to the material of its organic compound layer.
BACKGROUND ART
The recent rapid development in information media has created a large demand for display device innovation to enable rapid and precise conveyance of as much information as possible. In this present-day situation, self-emissive organic EL elements, which possess features such as high-speed response, high luminance, low power consumption, and reduced occupying space, have gained attention for use as elements in next generation flat panel displays and planar light sources, and much research has been directed to organic EL elements.
An organic EL element using organic compounds in its emissive layer is characterized in that it can emit light of a high luminance. By applying a direct current of several volts to a thin film element composed of a metal cathode and a fluorescent organic layer having a thickness of only about 100 nm formed on a transparent anode, a large current close to 1 A/cm
2
can be made to flow in the element. Efforts are being made to put such elements to practical use.
However, organic EL elements have not yet achieved sufficient stability and durability. Improvements in these points are indispensable for competing with of other types of displays.
It is known that the stability of the film structure of the organic thin film constituting the organic EL element significantly relates to the stability and durability of the element as a whole. In general, it is desirable that the organic thin film be made of a material that can be formed in an amorphous state and can maintain its amorphous state in a stable manner. However, crystallization begins to occur in an organic compound from the amorphous state when the glass transition temperature Tg is exceeded. Molecular movement is then activated, and the organic compound becomes unstable. Accordingly,to obtain a more stable organic thin film, it is necessary to develop a material having a high glass transition temperature Tg in addition to a high melting point Tm, and excellent heat resistance.
Four examples shown in
FIG. 1
are representative configurations of the presently known organic EL elements. The optimal element configuration for the organic compound layer between a cathode and an anode differs depending on the characteristics of the employed organic material. For example, in the element of FIG.
1
(
a
), a single emissive layer (EML) is disposed between a cathode and an anode, and this emissive layer also serves the functions of an electron transport layer (ETL) and a hole transport layer (HTL). In the element of FIG.
1
(
b
), the emissive layer simultaneously serves as the electron transport layer. The hole transport layer supplies holes into the emissive layer to generate light emission. In the element of FIG.
1
(
c
), the cathode supplies electrons to the electron transport layer. The anode supplies holes to the emissive layer which also functions as the hole transport layer. Light emission is generated near the interface between the emissive layer and the electron transport layer. In the element of FIG.
1
(
d
), electrons are supplied to the emissive layer from the electron transport layer, and holes from the hole transport layer. The electrons and the holes recombine within the emissive layer to emit light. Presently, appropriate organic compounds are being proposed for the organic layers of elements having these various configurations.
The organic compound layer constituting the organic thin film is composed using, as referenced to above, a compound having hole transport function, a compound having electron transport function, and a compound having emissive function. Though it is desirable that one compound possess all of these characteristics (see FIG.
1
(
a
)), usually a plurality of compounds are overlapped to form the organic compound layer (see FIG.
1
(
b
)-(
d
)).
A representative hole transport material is an aromatic amine compound. Especially, dimer of triphenylamine, TPD (triphenylamine dimer), is known as an exemplary hole transport material. TPD can be easily formed on a substrate as a uniform amorphous thin film by vacuum deposition. However, there is a problem with TPD in that its glass transition temperature Tg is low, at 60° C., and that TPD crystallizes even at room temperature after a long time, changing into an irregular film. Such a change in the film structure resulting from crystallization directly influences the life of EL elements. Provision of a hole transport material capable of maintaining a stable film configuration and having high glass transition temperature Tg is for this reason desired.
The same can be written about electron transport materials. Compounds including oxadiazole (PBD, BND) and triazole (TAZ) structures are known as electron transport materials. However, many of these materials also have low glass transition temperatures Tg and tend to crystallize. It is therefore difficult to achieve a stable element when these materials are used as the electron transport materials. Other problems of these materials, such as the requirement for a high drive voltage and insufficient durability, have also been pointed out.
Methods are recently proposed for raising the Tg of materials constituting an organic thin film. Such methods include introducing branches and non-planarity in the compound molecular structure to reduce intermolecular aggregation strength, thereby suppressing crystallizing property. Increasing the molecular weight is another of such methods. Polymers having starburst, Spiro, or linear structures, for example, are representative compounds obtained by those methods. A Spiro structure especially creates an extremely non-planar molecular structure, and use of this structure allows development of materials having high heat resistance. The Spiro compounds of tryphenylamine, oxadiazole, and oligophenylene, for example, can be hole transport, electron transport, and emissive materials, respectively.
Recently, a compound integrating spiro structure, in which branches and non-planarity are introduced into the molecular structure to reduce intermolecular aggregation strength and to thereby decrease crystallization property was presented by Hoechst (Polymer Preprints 38 (1997) 349). The compound presented here has the configuration denoted by the chemical formula below wherein two identical structural units are bonded, and demonstrates only one type of property.
The above Spiro compound shows excellent structural stability, but lacks flexibility (allows for little variety) in its molecular structure. Moreover, this material is insufficient in terms of its electronic property. When the basic unit of the material has electron transport property, the material only demonstrates electron transport property. The material only functions as an emissive material when the basic unit is emissive. It is therefore necessary to separately develop new compounds exclusively for each of the properties.
DISCLOSURE OF THE INVENTION
The present invention was created in the above light. The object of the present invention is to provide a new organic material having high heat resistance, into which properties such as electron transport property, hole transport property, and emissive property can be freely integrated as the property of the organic compound.
The electroluminescence element of the present invention is an organic EL element having an anode, a cathode, and one or more organic compound layers sandwiched between the anode and cathode, wherein at least one layer of the organic compound layers includes an organic compound having the structure in which two biphenyl derivatives are bonded, as denoted by chemical formula (1).
However, in the present invention, the above [A] does not include a structure composed of only a single carbon atom. In other words, the compound of chemical formula (1) does not include the structure in which two biphe

Affiliated with

Also associated with

Rating

Organic electroluminescent element 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 element, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Organic electroluminescent element will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2832298