Electric lamp and discharge devices – With luminescent solid or liquid material – Solid-state type
Reexamination Certificate
1999-01-13
2001-03-27
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With luminescent solid or liquid material
Solid-state type
C313S506000, C313S502000, C313S503000, C313S509000, C257S096000, C257S103000
Reexamination Certificate
active
06208076
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 electrode 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 electron blocking of the hole 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 hole injecting and transporting layers using organic materials, a long life, weather resistance, high stability, high efficiency, and low cost.
This and other objects are achieved by the present invention which is defined below.
(1) An organic electroluminescent device comprising a hole injecting electrode, a negative electrode, and at least two organic layers between the electrodes, said organic layers including a light emitting layer having a light emitting function,
said device further comprising a hole injecting and transporting layer containing a hole transporting organic material and an inorganic insulative hole injecting and transporting layer formed of an inorganic material between said hole injecting electrode and said light emitting layer,
said inorganic insulative hole injecting and transporting layer comprising silicon oxide or germanium oxide or a mixture of silicon oxide and germanium oxide as a main component, the main component having an average composition represented by the formula: (Si
1-x
Ge
x
)O
y
wherein 0≦x≦1 and 1<y≦2.
(2) The organic electroluminescent device of (1) wherein said inorganic insulative hole injecting and transporting layer satisfies 1.4≦y≦1.99.
(3) The organic electroluminescent device of (1) wherein said inorganic insulative hole injecting and transporting layer has a thickness of up to 5 nm.
(4) The organic electroluminescent device of (1) wherein said inorganic insulative hole injecting and transporting layer is formed between said light emitting layer and said hole injecting and transporting layer containing a hole transporting organic material.
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Y. Kurosaka, et al., Technical Report of IEICE, pp. 17-22, “Study On Enhanced Luminous Efficiency In Organic El Device—Effect Of Insertion Of Buffer Layer-”, Oct., 1998, (with English Abstract and Concise Explanation).
Y. Kurosaka, et al., Technical Report of IEICE, pp. 63-68, “Improvement Of Emission Characteristic Of Organic El Device”, Jul., 1998, Missing pp. 64, 66, and 68, which will be filed later, (With English Abstract and Concise Explanation).
Arai Michio
Kobori Isamu
Mitsuhashi Etsuo
Gerike Matthew J.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Patel Ashok
TDK Corporation
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