Organic EL element and organic EL display panel

1. An organic EL element, comprising:

an anode;

a cathode opposing the anode;

a light-emitting layer disposed between the anode and the cathode;

an electron transport layer disposed in contact with a cathode-side surface of the light-emitting layer; and

an electron injection layer disposed between the electron transport layer and the cathode, in contact with the electron transport layer,

wherein lowest unoccupied molecular orbital (LUMO) level of the electron transport layer is lower than at least one of LUMO level of the electron injection layer and Fermi level of a metal material included in the electron injection layer, and

film thickness of the electron injection layer is greater than film thickness of the electron transport layer.

2. The organic EL element of claim 1 ,

wherein the LUMO level of the electron transport layer is at least 0.3 eV lower than at least one of the LUMO level of the electron injection layer and the Fermi level of the metal material included in the electron injection layer.

3. The organic EL element of claim 1 ,

wherein a difference between LUMO level of the light-emitting layer and the LUMO level of the electron transport layer is at least 0.5 eV.

4. The organic EL element of claim 1 ,

wherein the metal material included in the electron injection layer is one of an alkali metal, an alkaline earth metal, and a transition metal.

5. The organic EL element of claim 4 ,

wherein the metal material included in the electron injection layer is barium.

6. The organic EL element of claim 1 ,

wherein an optical adjustment layer is disposed between the electron injection layer and the cathode.

7. The organic EL element of claim 6 ,

wherein the optical adjustment layer is a light-transmissive electrically-conductive film.

8. The organic EL element of claim 1 ,

wherein the anode is light-reflective, the cathode is light-transmissive, and light emitted from the light-emitting layer is emitted from the cathode side of the organic EL element.

9. An organic EL element comprising:

an anode;

a cathode opposing the anode;

a light-emitting layer disposed between the anode and the cathode;

an electron transport layer disposed in contact with a cathode-side surface of the light-emitting layer; and

an electron injection layer disposed between the electron transport layer and the cathode, in contact with the electron transport layer, wherein

the electron transport layer includes a metal material,

Fermi level of the metal material included in the electron transport layer is lower than at least one of lowest unoccupied molecular orbital (LUMO) level of the electron injection layer and Fermi level of a metal material included in the electron injection layer, and

film thickness of the electron injection layer is greater than film thickness of the electron transport layer.

10. The organic EL element of claim 9 ,

wherein the Fermi level of the metal material in the electron transport layer is at least 0.3 eV lower than at least one of the LUMO level of the electron injection layer and the Fermi level of the metal material included in the electron injection layer.

11. The organic EL element of claim 9 ,

wherein a difference between LUMO level of the light-emitting layer and the Fermi level of the metal material included in the electron transport layer is at least 0.5 eV.

12. An organic EL panel in which organic electroluminescence (EL) elements are arrayed on a substrate, each of the organic EL elements comprising:

an anode;

a cathode opposing the anode;

a light-emitting layer disposed between the anode and the cathode;

an electron transport layer disposed in contact with a cathode-side surface of the light-emitting layer; and

an electron injection layer disposed between the electron transport layer and the cathode, in contact with the electron transport layer, wherein

lowest unoccupied molecular orbital (LUMO) level of the electron transport layer is lower than at least one of LUMO level of the electron injection layer and Fermi level of a metal material included in the electron injection layer, and

film thickness of the electron injection layer is greater than film thickness of the electron transport layer.

13. The organic EL panel of claim 12 ,

wherein the substrate is a flexible substrate.

14. The organic EL panel of claim 12 ,

wherein the electron injection layer is a continuous layer across the plurality of the organic EL element.