Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
2001-11-08
2004-12-07
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S504000, C313S506000, C313S512000, C257S088000, C257S093000, C257S100000
Reexamination Certificate
active
06828727
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a phosphor in which luminescence generated by applying electric field (electro luminescence) and to a light emitting device using the phosphor. In particular, the present invention relates to a light emitting device in which an organic compound is used for a phosphor. Fluorescence and phosphorescence are included in the electro luminescence. The present invention relates to a light emitting device to which light emission by one or both of the fluorescence and phosphorescence is applied.
2. Description of the Related Art
A back light or a front light is used as the typical form of a display device using liquid crystal, and the structure is such that an image is displayed by means of the light. The liquid crystal display device is adopted as an image displaying means in various electronic devices, but has a defect from the viewpoint of its structure that a viewing angle is narrow. On the contrary, a display device using a phosphor in which electro luminescence is obtained has a wide viewing angle and is excellent in visibility. Thus, the display device using a phosphor has attracted attention as the display device in the next generation.
A light emitting element in which an organic compound is used for a phosphor (hereinafter referred to as organic light emitting element) is structured by appropriately combining a hole injecting layer, a hole transporting layer, a light emitting layer, an electron transporting layer, and an electron injecting layer, which are formed by the organic compound, between a cathode and an anode. Here, the hole injecting layer and the hole transporting layer are separately shown, but these are the same in a meaning that a hole transporting property (hole mobility) is particularly an important characteristic. In order to distinguish these layers for convenience, the hole injecting layer indicates the layer that contacts the anode, and the layer that contacts the light emitting layer is referred to as the hole transporting layer. Further, the layer that contacts the cathode is referred to as the electron injecting layer, and the layer that contacts the light emitting layer is referred to as the electron transporting layer. The light emitting layer may also serve as the electron transporting layer, and thus, is also referred to as a light emitting electron transporting layer. The light emitting element formed by combining these layers shows a rectification characteristic, and has the same structure as a diode.
The light emitting mechanism is considered such that an electron injected from the cathode and a hole injected from the anode are recombined in a layer comprised of a phosphor (light emitting layer) to form an exciton, and the exciton emits light when returning to a base state. There are emission of light from a singlet excitation state (fluorescence) and emission of light from a triplet excitation state (phosphorescence). Luminance reaches several thousands to several tens of thousands cd/m
2
. Thus, it is considered that the light emission mechanism can be applied to a display device and the like in principle. However, various types of deterioration phenomena exist, and remain as a problem that impedes putting of the display device and the like to practical use.
The deterioration of the phosphor comprised of the organic compound or the organic light emitting element is considered to arise from the five factors mentioned below. The factors are (1) chemical deterioration of the organic compound (through the excitation state), (2) melting of the organic compound due to heat generation at the time of drive, (3) dielectric breakdown caused by a macro defect, (4) deterioration of an electrode or an interface of the electrode and an organic layer and (5) deterioration that arises from instability in an amorphous structure of the organic compound.
The above factors (1) to (3) are caused by driving the organic light emitting element. Heat is inevitably generated by such that a current in the element is converted into Joule heat. It is considered that melting occurs when the melting point or the glass transition temperature of the organic compound is low. Further, electric field is concentrated on the portion where a pin hole or a scratch exists, whereby the dielectric breakdown occurs. As to the factors (4) and (5), the deterioration progresses even if the phosphor comprised of the organic compound or organic light emitting element is preserved at a room temperature. The factor (4) is known as a dark spot, and arises from oxidization and reaction with moisture of a cathode. As to the factor (5), the organic compound used in the organic light emitting element is an amorphous material, and it is considered that almost no amorphous material exists in which the amorphous structure is kept stable since amorphous materials are crystallized by the long preservation, change through the elapse of time and heat generation.
The dark spot has been considerably suppressed because of the improvement of a sealing technique. However, the actual deterioration is occurred with the combination of the above factors, and thus, it is difficult to commonly understand the actual deterioration. The typical sealing technique is known as a method of making an organic light emitting element formed on a substrate airtight by a sealing member and providing a drying agent in the space. However, it is considered that the phenomenon, in which not only the current flowing through the organic light emitting element but also the emission luminance are towered when a constant voltage is continuously applied, originates in the property of the organic compound.
A low molecular weight organic compound and a polymer organic compound are both known as an organic compound for forming an organic light emitting element. As one example of the low molecular weight organic compound, copper phthalocyanine (CuPc), or á-NPD (4,4′-bis-[N-(naphthyl)-N-phenyl-amino]biphenyl) or MTDATA (4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine), which is an aromatic amine-based material is known as the hole injecting layer, and tris-8-quinolinolate-aluminum complex (Alq
3
) or the like is known as the light emitting layer. As the polymer organic light emitting material, polyaniline, polythiophene derivative (PEDOT) or the like is known.
It is considered that the low molecular weight organic compound formed by an evaporation method has remarkable variety in comparison with the polymer organic material from the viewpoint of the variety of materials. However, in any case, the organic compound constituted of only a basic structural unit is rare. There may be the cases where different kinds of the organic compounds are combined, an impurity is mixed into the organic compound in a manufacturing process, and various additives such as a pigment are added to the organic compound. Further, among these materials, a material deteriorated due to moisture, a material easily oxidized and the like are included. Moisture and oxygen can be easily mixed from an atmosphere. Thus, care needs to be taken in handling the materials.
It is known that chemical bond is changed into double bond and the structure containing oxygen (—OH, —OOH, >C═O, —COOH and the like) when the organic compound is subjected to light deterioration. Therefore, in the case where the organic compound is provided in the atmosphere containing oxygen, or in the case where oxygen or H
2
O as an impurity is included in the organic compound, it is considered that the bond state changes, and the deterioration is promoted.
In the field of a semiconductor technique, in a semiconductor element having semiconductor junction, such as a diode, an impurity that arises from oxygen forms a local level in a forbidden band, which is a cause of junction leakage reduction and lifetime of or carrier. Thus, it is known that the impurity remarkably reduces the characteristics of the semiconductor element.
Oxygen molecules are peculiar molecules in a base state
Fish & Richardson P.C.
Patel Ashok
Santiago Mariceli
Semiconductor Energy Laboratory Co,. Ltd.
LandOfFree
Light emitting device comprising a partition layer having an... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Light emitting device comprising a partition layer having an..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Light emitting device comprising a partition layer having an... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3318576