Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-01-13
2001-03-06
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C257S096000, C257S103000, C313S502000, C313S503000, C313S509000
Reexamination Certificate
active
06198219
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
This invention relates to an organic electroluminescent (EL) device and more particularly, to an inorganic/organic junction structure suitable for use in a device of the type wherein an electric field is applied to a thin film of an organic compound to emit light.
2. Background Art
In general, organic EL devices have a basic configuration including a glass substrate, a transparent electrode of ITO etc., a hole transporting layer of an organic amine compound, an organic light emitting layer of a material exhibiting electronic conductivity and intense light emission such as Alq3, and an electrode of a low work function metal such as MgAg, wherein the layers are stacked on the substrate in the described order.
The device configurations which have been reported thus far have one or more organic compound layers interposed between a hole injecting electrode and an electron injecting electrode. The organic compound layers are typically of two- or three-layer structure.
Included in the two-layer structure are a structure having a hole transporting layer and a light emitting layer formed between the hole injecting electrode and the electron injecting electrode and another structure having a light emitting layer and an electron transporting layer formed between the hole injecting electrode and the electron injecting electrode. Included in the three-layer structure is a structure having a hole transporting layer, a light emitting layer, and an electron transporting layer formed between the hole injecting electrode and the electron injecting electrode. Also known is a one-layer structure wherein a single layer playing all the roles is formed from a polymer or a mixed system.
FIGS. 3 and 4
illustrate typical configurations of organic EL devices.
In
FIG. 3
, a hole transporting layer
14
and a light emitting layer
15
of organic compounds are formed between a hole injecting electrode
12
and an electron injecting electrode
13
on a substrate
11
. In this configuration, the light emitting layer
15
also serves as an electron transporting layer.
In
FIG. 4
, a hole transporting layer
14
, a light emitting layer
15
, and an electron transporting layer
16
of organic compounds are formed between a hole injecting electrode
12
and an electron injecting electrode
13
on a substrate
11
.
Attempts have been made to improve the luminous efficiency of these organic EL devices. With the prior art device configuration, however, for reasons of poor hole blocking of the electron injecting and transporting layer, it was difficult to achieve efficient recombination of electrons with holes in the light emitting layer and hence, to provide a device with a fully satisfactory efficiency.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an organic EL device having better performance than prior art devices having electron injecting and transporting layers using organic materials, a high efficiency, long life, weather resistance, and high stability.
This and other objects are achieved by the present invention which is defined below.
(1) An organic electroluminescent device comprising a substrate, a hole injecting electrode and a negative electrode formed on the substrate, and an organic layer containing an organic material between the electrodes, said organic layer including a light emitting layer having at least a light emitting function,
said device further comprising an electron injecting and transporting layer containing an electron transporting organic material and an inorganic insulative electron injecting and transporting layer formed of an inorganic material between said negative electrode and said light emitting layer,
said inorganic insulative electron injecting and transporting layer comprising at least one oxide selected from the group consisting of lithium oxide, rubidium oxide, potassium oxide, sodium oxide, cesium oxide, strontium oxide, magnesium oxide, and calcium oxide as a main component, and silicon oxide, germanium oxide or a mixture of silicon oxide and germanium oxide as a stabilizer.
(2) The organic electroluminescent device of (1) wherein said inorganic insulative electron injecting and transporting layer contains 80 to 99 mol % of the main component and 1 to 20 mol % of the stabilizer, based on the entire components.
(3) The organic electroluminescent device of (1) wherein said inorganic insulative electron injecting and transporting layer has been formed by sputtering.
(4) The organic electroluminescent device of (1) wherein said inorganic insulative electron injecting and transporting layer has a thickness of up to 1 nm.
(5) An organic electroluminescent device comprising a substrate, a hole injecting electrode and a negative electrode formed on the substrate, and an organic layer containing an organic material between the electrodes, said organic layer including a light emitting layer having at least a light emitting function,
said device further comprising an electron injecting and transporting layer containing an electron transporting organic material and an inorganic insulative electron injecting and transporting layer formed of an inorganic material between said negative electrode and said light emitting layer,
said inorganic insulative electron injecting and transporting layer comprising at least one alkali metal element selected from the group consisting of Li, Na, K, Rb, Cs, and Fr, and at least one alkaline earth metal element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.
(6) The organic electroluminescent device of (5) further comprising silicon oxide, germanium oxide or a mixture of silicon oxide and germanium oxide.
(7) The organic electroluminescent device of (5) wherein said inorganic insulative electron injecting and transporting layer has been formed by sputtering.
(8) The organic electroluminescent device of (5) wherein said inorganic insulative electron injecting and transporting layer has a thickness of up to 1 nm.
Technical Report of IEICE OME98-87, OPE98-81 (1998-10) discloses a device structure in which a buffer layer of SiO, Al
2
O
3
, LiF or the like is interposed between a light emitting layer or hole transporting layer and an anode or between a light emitting layer and a cathode. When the buffer layer is interposed to adjoin the hole transporting layer, the buffer layer fills in irregularities at the interface of the hole transporting layer to improve efficiency. When the buffer layer is interposed to adjoin the anode, the buffer layer restrains injection of holes for equalizing the numbers of electrons and holes to improve efficiency. Also, when an alkali halide such as LiF or NaCl is interposed on the negative electrode side, the trap level that the alkali halide possesses offers hopping sites for facilitating electron injection upon forward biasing and hole injection upon reverse biasing.
Therefore, the organic EL device construction of the above reference is different from the inorganic-organic electron injecting and transporting layer structure of the present invention in which recombination in the light emitting layer is increased by enhancing the hole blockage. Also, Al
2
O
3
, LiF, NaCl or the like is different in material and composition from the inorganic insulating electron injecting and transporting layer of the present invention. Further, silicon monoxide (SiO) has poor hole blockage. Fluorides such as LiF can corrode the metal of which the negative electrode is made, resulting in a reduced device life.
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Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Gerike Matthew J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
TDK Corporation
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