Organic electroluminescence device

Details Organic electroluminescence device Organic electroluminescence device

1993-02-03

1994-08-09

Ryan, Patrick J.

Stock material or miscellaneous articles

Structurally defined web or sheet

Discontinuous or differential coating, impregnation or bond

428460, 428690, 428917, 313503, 313504, B32B 900

Patent

active

053365461

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

1. Technical Field
The present invention relates to an organic electroluminescence device. More particularly, it relates to an organic electroluminescence device wherein high brightness, high luminous efficiency and long lifetime can be attained by using an oxadiazole or a thiadiazole compound as a component of an organic electroluminescence device.
2. Background Art
As an organic electroluminescence device (hereinafter referred to as an organic EL device), the one described in the specification of U.S. Pat. No. 3,995,299 has heretofore been known. The structure of said organic EL device is anode/positive hole injecting layer/polymer/electron injecting layer/cathode. The concept of positive hole injection layer` was first proposed therein. In this case, as a representative example of a polymer used as a light emitting layer was polyvinylcarbazole. The positive hole (hereinafter referred to as "hole") injecting layer works as an electric conducting layer in which cations exist, formed by adding a strong electron-accepting compound to the above polymer. Said hole injecting layer can inject holes to the above polymer in an applied electric field.
The electron injecting layer is an electric conducting layer in which anions exist, formed by adding a strong electron-donating compound. Said electron injecting layer can inject electrons to the above polymer in an applied electric field.
Moreover, according to E. H. Partridge, Polymer, 24,748 (1983), a hole injecting layer and an electron injecting layer are disclosed in detail, and it is shown that electrons and holes can be injected to an organic insulator by the above layers at lower voltages.
According to the above process, however, as a strong electron-donating compound, a metal such as Ce, which is readily oxidized, is used, so stable light emission could not always be obtained. Besides, since an oxidant such as AlCl.sub.3 is used as an electron-accepting compound, stable light emitting action could not be obtained because of mobile ions such as AlCl.sub.4.sup.- in an higher electric field.
On the other hand, the specification of U.S. Pat. No. 4,720,432 (Japanese Patent Application Laid-Open No. 295695/1988) discloses a device which has a structure as anode/hole injecting zone/hole transporting zone/electron transporting zone/cathode, and which uses a porphyrin compound for a hole injecting zone and a triphenylamine derivative for a hole transporting zone. In the device, the electron transporting zone is a light emitting zone, in which a 3-coordination 8-hydroxyquinoline complex such as a metal chelate oxanoide compound is used. The use of said device can make its lifetime several hundred hours longer, but enough lifetime cannot yet be obtained. This is because a triphenylamine derivative as the material for hole injecting is readily oxidized and also is weak in heat generation during the light emission.
Moreover, according to the specification of U.S. Pat. No. 4,950,950, the lifetime of the device was improved by using a silazane derivative in place of the above triphenylamine derivative. The brightness of the device after about 200-hour running is maintained to 80% of 140 cd/m.sup.2 of its initial brightness, which is still insufficient performance.
In the prior arts described above, the electron transporting layer is a light emitting layer, but the combination of the device constituting elements defines the function of each layer.
Various structures of device are possible, but a device having a structure of anode/hole injecting layer/light emitting layer/electron injecting layer/cathode will be explained as an example.
It is considered that putting an electron injecting layer in the device structure promotes electrons to flow from the cathode to the light emitting layer, and the electrons recombine with most of the holes injected to the light emitting layer, resulting in higher luminous efficiency. Moreover, when an energy barrier exists between the light emitting layer and the electron injecting layer, the injected holes are enclosed in the l

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