Organic electroluminescent device

1. An organic electroluminescent device comprising:

an anode electrode layer;

a cathode electrode layer opposed to the anode electrode layer; and

an organic structure including at least one light-emissive unit, each light-emissive unit having a hole injection layer on an anode, a hole transportation layer adjacent the hole injection layer, a light-emissive layer adjacent the hole transportation layer, and an electron injection layer adjacent the light-emissive layer on a cathode side, the organic structure further including a charge generation layer partitioning each light-emissive unit from a subsequent light-emissive unit;

wherein the hole injection layer is capable of diminishing an energy barrier generated during injection of holes from the anode;

wherein at least one of the anode electrode layer and the cathode electrode layer is transparent;

wherein the hole injection layer consists essentially of a mixed layer of a metal oxide and an organic compound, and the thickness of the hole injection layer is at least about three hundred (300) angstroms;

wherein the mixed layer is formed upon co-deposition of the metal oxide and the organic compound at a molar ratio of about 4:1;

wherein the mixed layer acts as a damage-diminishing layer;

wherein the organic compound in the mixed layer comprises an arylamine compound represented by the general formula (I):

wherein Ar.sub.1, Ar.sub.2 and Ar.sub.3 each independently represents an aromatic hydrocarbon group which can be substituted and wherein the organic compound has an ionization potential of less than 5.7 eV and has a hole transporting property;

wherein the mixed layer includes a charge transfer complex having a radical cation of the organic compound and a radical anion of the metal oxide, the charge transfer complex being produced upon an oxidation-reduction reaction between the metal oxide and the organic compound; and

wherein the radical cation in the charge transfer complex is moved to a direction of the cathode electrode layer during application of the voltage to the EL device, thereby injecting holes in the light-emissive layer.

2. The organic electroluminescent device according to claim 1 , wherein the organic compound is a porphyrin compound including a phthalocyanine derivative.

3. The organic electroluminescent device according to claim 1 , wherein the organic compound is an arylamine compound having a glass transition temperature of not less than 90° C.

4. The organic electroluminescent device according to claim 3 , wherein the arylamine compound used as the organic compound comprises one of α-NPD, 2-TNATA, spiro-TAD and spiro-NPB.

5. The organic electroluminescent device according to claim 1 , wherein the metal oxide comprises one of V 2 O 5 and Re 2 O 7 .

6. The organic electroluminescent device according to claim 1 , wherein the EL device comprises a substrate having laminated thereon the anode electrode layer, the hole injection layer, and an organic structure including the light-emissive layer and the cathode electrode layer, in that order.

7. The organic electroluminescent device according to claim 1 , wherein the EL device comprises a substrate having laminated thereon the cathode electrode layer, an organic structure comprising the light-emissive layer, the hole injection layer and the anode electrode layer, in that order.

8. The organic electroluminescent device according to claim 6 , wherein a mixing ratio of the metal oxide and the organic compound in the hole injection layer is continuously varied from the anode electrode layer to the organic structure including the light-emissive layer.

9. The organic electroluminescent device according to claim 7 , wherein a mixing ratio of the metal oxide and the organic compound in the hole injection layer is continuously varied from the anode electrode layer to the organic structure including the light-emissive layer.

10. The organic electroluminescent device according to claim 6 , wherein a mixing ratio of the metal oxide and the organic compound in the hole injection layer is discontinuously varied from the anode electrode layer to the organic structure including the light-emissive layer.

11. The organic electroluminescent device according to claim 7 , wherein a mixing ratio of the metal oxide and the organic compound in the hole injection layer is discontinuously varied from the anode electrode layer to the organic structure including the light-emissive layer.

12. The organic electroluminescent device according to claim 7 , wherein the anode electrode layer is formed with a sputtering method, and the mixed layer acts as a buffer layer for reducing damage of the EL device during the sputtering process.

13. The organic electroluminescent device according to claim 12 , wherein a sputtering apparatus used in the sputtering method comprises a facing target sputtering system which includes a pair of opposed targets provided at a predetermined distance apart, a reflection electrode capable of reflecting electrons towards a front peripheral area of each target, and a magnetic field generation medium capable of forming a parallel magnetic field in a neighborhood of the peripheral portion of each target, the magnetic field having a portion parallel to the peripheral portion of the target.

14. The organic electroluminescent device according to claim 1 , wherein the metal oxide is vaporized with one of a resistive heating vapor deposition method, an electron beam vapor deposition method and a laser beam vapor deposition method.

15. The organic electroluminescent device according to claim 1 , wherein the hole injection layer which is a mixed layer of the metal oxide and the organic compound has a resistivity of not less than 1.0×10 2 Ωcm and less than 1.0×10 10 Ωcm.

16. An organic electroluminescent device comprising:

an anode electrode layer;

a cathode electrode layer opposed to the anode electrode layer;

an organic structure including at least one light-emissive unit, each light-emissive unit having a hole injection layer on an anode, a hole transportation layer adjacent the hole injection layer, a light-emissive layer adjacent the hole transportation layer, and an electron injection layer adjacent the light-emissive layer on a cathode side, and the organic structure further including a charge generation layer adjacent the electron injection layer and partitioning the at least one light-emissive unit;

wherein the hole injection layer is capable of diminishing an energy barrier generated during injection of holes from the anode;

wherein at least one of the anode electrode layer and the cathode electrode layer is transparent;

wherein the hole injection layer consists essentially of a mixed layer of a metal oxide and an organic compound, and the thickness of the hole injection layer is at least about three hundred (300) angstroms;

wherein the mixed layer is formed upon co-deposition of the metal oxide and the organic compound at a molar ratio of about 4:1;

wherein the organic compound in the mixed layer comprises an arylamine compound represented by the general formula (I):

wherein Ar 1 , Ar 2 and Ar 3 each independently represents an aromatic hydrocarbon group which can be substituted and the organic compound has an ionization potential of less than 5.7 eV and has a hole transporting property;

wherein the mixed layer includes a charge transfer complex having a radical cation of the organic compound and a radical anion of the metal oxide, the charge transfer complex being produced upon an oxidation-reduction reaction between the metal oxide and the organic compound; and

wherein the radical cation in the charge transfer complex is moved to a direction of the cathode electrode layer during application of the voltage to the EL device, thereby injecting holes in the light-emissive layer.