Organic electroluminescence element having concentration variation of hole transporting light-emitting material

1. An organic electroluminescence element comprising an organic layer comprising a light-emitting layer disposed between a pair of electrodes, wherein the light-emitting layer comprises at least one hole-transporting light-emitting material and at least one electron-transporting host material, and a concentration of the hole-transporting light-emitting material in the light-emitting layer decreases from an anode side toward a cathode side;

wherein the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present at the entire light-emitting layer, and a concentration of the at least one hole-transporting light-emitting material decreases from an anode side toward a cathode side within the entire light-emitting layer at which the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present; and

wherein a ratio of the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the cathode side relative to the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the anode side (concentration of hole-transporting light-emitting material in interface region on cathode side/concentration of hole-transporting light-emitting material in interface region on anode side) is from 0% to 30%.

2. The organic electroluminescence element according to claim 1 , wherein the concentration of the hole-transporting light-emitting material in the light-emitting layer is 10% by weight or less in the interface region of the light-emitting layer on the cathode side.

3. The organic electroluminescence element according to claim 1 , wherein the hole-transporting light-emitting material is a phosphorescent light-emitting material.

4. The organic electroluminescence element according to claim 3 , wherein the hole-transporting light-emitting material is an Ir complex.

5. The organic electroluminescence element according to claim 1 , wherein the electron-transporting host material is a Be complex, an Al complex, a Ga complex, a Zn complex, a Pt complex, a Pd complex or a nitrogen-containing aromatic heterocyclic compound.

6. The organic electroluminescence element according to claim 1 , wherein a concentration of the electron-transporting host material in the light-emitting layer decreases from the cathode side toward the anode side.

7. The organic electroluminescence element according to claim 6 , wherein a ratio of the concentration of the electron-transporting host material in an interface region of the light-emitting layer on the anode side relative to the concentration of the electron-transporting host material in an interface region of the light-emitting layer on the cathode side (concentration of electron-transporting host material in interface region on anode side/concentration of electron-transporting host material in interface region on cathode side) is from 0% to 90%.

8. The organic electroluminescence element according to claim 7 , wherein the concentration of the electron-transporting host material in the light-emitting layer is 90% by weight or less in the interface region of the light-emitting layer on the anode side.

9. The organic electroluminescence element according to claim 8 , wherein the hole-transporting light-emitting material is a phosphorescent light-emitting material.

10. The organic electroluminescence element according to claim 9 , wherein the hole-transporting light-emitting material is an Ir complex.

11. The organic electroluminescence element according to claim 6 , wherein the electron-transporting host material is a Be complex, an Al complex, a Ga complex, a Zn complex, a Pt complex, a Pd complex or a nitrogen-containing aromatic heterocyclic compound.

12. An organic electroluminescence element comprising an organic layer comprising a light-emitting layer disposed between a pair of electrodes, wherein the light-emitting layer comprises at least one hole-transporting light-emitting material and at least one electron-transporting host material, and a concentration of the hole-transporting light-emitting material in the light-emitting layer decreases stepwise from an anode side toward a cathode side;

wherein the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present at the entire light-emitting layer, and a concentration of the at least one hole-transporting light-emitting material decreases stepwise from an anode side toward a cathode side within the entire light-emitting layer at which the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present; and

wherein a ratio of the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the cathode side relative to the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the anode side (concentration of hole-transporting light-emitting material in interface region on cathode side/concentration of hole-transporting light-emitting material in interface region on anode side) is from 0% to 30%.

13. An organic electroluminescence element comprising an organic layer comprising a light-emitting layer disposed between a pair of electrodes, wherein the light-emitting layer comprises at least one hole-transporting light-emitting material and at least one electron-transporting host material, and a concentration of the hole-transporting light-emitting material in the light-emitting layer decreases in a wave pattern from an anode side toward a cathode side;

wherein the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present at the entire light-emitting layer, and a concentration of the at least one hole-transporting light-emitting material decreases in a wave pattern from an anode side toward a cathode side within the entire light-emitting layer at which the at least one hole-transporting light-emitting material and the at least one electron-transporting host material are simultaneously present; and

wherein a ratio of the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the cathode side relative to the concentration of the hole-transporting light-emitting material in an interface region of the entire light-emitting layer on the anode side (concentration of hole-transporting light-emitting material in interface region on cathode side/concentration of hole-transporting light-emitting material in interface region on anode side) is from 0% to 30%.