Organic electroluminescent element
View Patent ↗Provided is an organic electroluminescent element superior in long-term durability and lifetime characteristics. The organic electroluminescent element has a structure where plurality of light-emitting layers formed via an intermediate layer are interposed between a positive electrode and a negative electrode. The intermediate layer has a mixed layer, a first layer, and a hole-injection layer which are formed in this order from the positive electrode to the negative electrode, the mixed layer containing an electron-donating substance and an electron-transporting organic material, and the first layer being made of an electron-transporting material. The first layer has a thickness in a range of 0.2 to 2.0 nm. The hole-injection layer consists of an electro-accepting organic material.
1. An organic electroluminescent element, comprising:
a plurality of light-emitting layers between positive and negative electrodes; and
an intermediate layer interposed between the plurality of light emitting layers,
wherein the intermediate layer includes a mixed layer, a first layer and a hole injection layer which are formed in order from the positive electrode to the negative electrode, the mixed layer containing an electron-donating substance and an electron-transporting organic material, the first layer being made of electron-transporting organic material,
the first layer has a thickness in a range of 0.2 to 20 nm,
the hole injection layer consists of an electron-accepting organic material,
the electron-donating substance includes metal lithium,
the mixed layer is a mixed film of the metal lithium and the electron-transporting organic material, and
the mixed film is formed at one time by a vacuum evaporator.
2. The organic electroluminescent element according to claim 1 , wherein
the electron-accepting organic material is 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile.
3. The organic electroluminescent element according to claim 2 , further comprising:
a second layer made of electron-transporting organic material interposed between the positive electrode and the mixed layer,
wherein the electron transporting organic material contained in the mixed layer, the electron-transporting organic material forming the first layer, and the electron-transporting organic material forming the second layer comprise a same material.
4. The organic electroluminescent element according to claim 1 , further comprising:
a second layer made of electron-transporting organic material interposed between the positive electrode and the mixed layer,
wherein the electron transporting organic material contained in the mixed layer, the electron-transporting organic material forming the first layer, and the electron-transporting organic material forming the second layer comprise a same material.
5. The organic electroluminescent element according to claim 1 , wherein
the mixed layer is directly on a first one of the plurality of light-emitting layers,
the first layer is directly on the mixed layer,
the hole injection layer is directly on the first layer, and
a second one of the plurality of light-emitting layers is directly on the hole injection layer.
6. The organic electroluminescent element according to claim 1 , wherein
a content of the electron-donating substance in the mixed layer is in a range of 5 to 50 molar percent of the mixed layer, and
a content of the electron-transporting organic material in the mixed layer is in a range of 95 to 50 molar percent of the mixed layer.
7. The organic electroluminescent element according to claim 1 , wherein
a molar ratio of the electron-donating substance and the electron-transporting organic material is 1:1.
8. The organic electroluminescent element according to claim 1 , wherein
the mixed layer has a thickness in a range of 0.5 to 20 nm.
9. The organic electroluminescent element according to claim 1 , wherein
the electron-donating substance is mixed uniformly in the mixed layer.
10. The organic electroluminescent element according to claim 1 , wherein
the electron-donating substance is disposed in predetermined regions of the mixed layer.
11. The organic electroluminescent element according to claim 10 , wherein
the electron-donating substance is disposed in an intermediate region of the mixed layer.
12. The organic electroluminescent element according to claim 10 , wherein
the electron-donating substance is disposed in a region proximate to an interface between the mixed layer and the first layer.
13. The organic electroluminescent element according to claim 1 , wherein
the hole injection layer has a thickness in a range of 0.5 to 20 nm.
14. The organic electroluminescent element according to claim 1 , further comprising:
a hole-transporting layer formed on the hole injection layer and interposed between the intermediate layer and one of the plurality of light-emitting layers.
15. The organic electroluminescent element according to claim 1 , wherein
no metal oxide is used in any layer of the intermediate layer.
16. The organic electroluminescent element according to claim 1 , wherein
the plurality of light-emitting layers comprises at least three light-emitting layers, and
the organic electroluminescent element further comprises a plurality of the intermediate layer, each of the plurality of the intermediate layer being interposed between a pair of the plurality of light-emitting layers.