Organic electroluminescent device

Details Organic electroluminescent device Organic electroluminescent device

1999-01-29

2001-09-04

Harris Kelly, Cynthia (Department: 1774)

Stock material or miscellaneous articles

Composite

Of inorganic material

C428S917000, C313S504000, C313S505000, C313S506000

Reexamination Certificate

active

06284394

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
Organic EL devices have enabled to form a device of large area on a glass, and considerable research and development on such organic EL devices have gone on for their use as a display. 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 an excellent electron and hole injecting efficiency and improved light emitting efficiency, which can be manufactured at reduced cost and which can be operated at low drive voltage.
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 one organic layer between the electrodes; wherein
at least one of said at least one organic layer has a light emitting function;
a high resistivity inorganic electron injecting layer is provided between said light emitting layer and said negative electrode,
said high resistivity inorganic electron injecting layer comprising
a first component having a work function of up to 4 eV which is oxide of at least one member selected from alkaline metal elements, alkaline earth metal elements, and lanthanoid elements, and
a second component having a work function of 3 to 5 eV which is at least one metal, and
said high resistivity inorganic electron injecting layer having conduction paths for hole blockage and electron transportation; and
an inorganic insulative hole injecting and transporting layer is provided between said light emitting layer and said hole injecting layer,
said inorganic insulative hole injecting and transporting layer containing oxide of silicon and/or germanium as its main component, and said main component having an average composition of:
(Si
1−x
Ge
x
)O
y
wherein 0≦x≦1 and 1.7≦y≦1.99.
(2) The organic electroluminescent device of (1) wherein said second component is at least one member selected from Zn, Sn, V, Ru, Sm and In.
(3) The organic electroluminescent device of (1) wherein said alkaline metal element is at least one member selected from Li, Na, K, Rb, Cs, and Fr; said alkaline earth metal element is at least one member selected from Mg, Ca and Sr; and said lanthanoid element is at least one member selected from La and Ce.
(4) The organic electroluminescent device of (1) wherein said high resistivity hole injecting layer has a resistivity of 1 to 1×10
11
&OHgr;·cm.
(5) The organic electroluminescent device of (1) wherein said high resistivity inorganic electron injecting layer contains 0.2 to 40 mol % of said second component based on the entire components.
(6) The organic electroluminescent device of (1) wherein said high resistivity inorganic electron injecting layer has a thickness of 0.3 to 30 nm.
(7) The organic electroluminescent device of (1) wherein said inorganic insulative hole injecting and transporting layer further comprises silicon oxide and/or germanium oxide as its stabilizer.
(8) The organic electroluminescent device of (1) wherein said inorganic insulative hole injecting and transporting layer has a thickness of 0.1 to 5 nm.


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