Organic light emitting device

1. An organic light emitting device, comprising:

a first electrode;

a second electrode; and

an emission layer arranged between the first electrode and the second electrode, the emission layer comprising at least two electron transport materials adapted to serve as a host and a phosphorescent dopant, wherein the at least two electron transport materials have different highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, wherein a HOMO energy level of at least one of the at least two electron transport materials is lower than a HOMO energy level of the phosphorescent dopant, and a LUMO energy level of at least one of the at least two electron transport materials is greater than a LUMO energy level of the phosphorescent dopant.

2. An organic light emitting device, comprising:

a first electrode;

a second electrode; and

an emission layer arranged between the first electrode and the second electrode, the emission layer comprising at least two electron transport materials adapted to serve as a host and a phosphorescent dopant, wherein one of the at least two electron transport materials comprises 2,5-dispirofluorene-1,3,4-oxadiazole spirofluorene compound.

3. The organic light emitting device of claim 1 , wherein one of the at least two electron transport materials comprises at least a metal-organic complex.

4. The organic light emitting device of claim 3 , wherein the metal-organic complex comprises at least a compound selected from the group consisting of BAlq, bis(8-hydroxyquinolato)biphenoxy metal, bis(8-hydroxyquinolato)phenoxy metal, bis(2-methyl-8-hydroxyquinolato)biphenoxy metal, bis(2-methyl-8-hydroxyquinolato)phenoxy metal, bis(2-methyl-8-quinolinolato)(para-phenyl-phenolato) metal, and bis(2-(2-hydroxyphenyl)quinolato) metal.

5. The organic light emitting device of claim 1 , wherein the emission layer is comprised of 70 to 99 parts by weight of the host and 1 to 30 parts by weight of the phosphorescent dopant based on 100 parts by weight of materials forming the emission layer.

6. The organic light emitting device of claim 1 , wherein a weight ratio of one of the at least two electron transport materials to another of the at least two electron transport materials is in the range of 1:9 to 9:1.

7. The organic light emitting device of claim 1 , wherein the phosphorescent dopant is comprised of a compound selected from the group consisting of bisthienylpyridine acetylacetonate Iridium, bis(benzothienylpyridine)acetylacetonate Iridium, bis(2-phenylbenzothiazole)acetylacetonate Iridium, bis(1-phenylisoquinoline)Iridium acetylacetonate, tris(1-phenylisoquinoline) iridium, tris(phenylpyridine) iridium, tris(2-biphenylpyridine)iridium, tris(3-biphenyl pyridine)iridium, tris(4-biphenyl pyridine)iridium, and Ir(pq) 2 (acac) where pq denotes 2-phenylquinoline and acac denotes acetylacetone.

8. The organic light emitting device of claim 1 , further comprising at least one layer arranged between the first electrode and the emission layer, the at least one layer comprising a layer selected from the group consisting of a hole injection layer and a hole transport layer.

9. The organic light emitting device of claim 1 , further comprising at least one layer arranged between the emission layer and the second electrode, the at least one layer comprising a layer selected from the group consisting of a hole blocking layer, an electron transport layer, and an electron injection layer.

10. The organic light emitting device of claim 1 , wherein the emission layer is comprised of a spirofluorene compound, an aluminum complex and a phosphorescent dopant.

11. The organic light emitting device of claim 10 , wherein the spirofluorene compound comprises 2,5-dispirobifluorene-1,3,4-oxadiazole, and the aluminum complex comprises BAlq.

12. The organic light emitting device of claim 10 , wherein and an amount of the phosphorescent dopant is in the range of 5 to 15 parts by weight based on 100 parts by weight of materials forming the emission layer, the phosphorescent dopant comprises Ir(pq) 2 (acac) where pq denotes 2-phenylquinoline and acac denotes acetylacetone.

13. The organic light emitting device of claim 10 , wherein a weight ratio of the spirofluorene compound to the aluminum complex is in the range of 1:2 to 1:4.

14. The organic light emitting device of claim 1 , the at least two electron transport materials being different from each other.

15. A method of making an organic light emitting device, comprising:

providing a transparent glass substrate;

forming an anode on the transparent glass substrate by applying a thin transparent conductive layer on the glass substrate;

forming a hole injection layer on the anode;

forming a hole transport layer on the hole injection layer;

forming an emission layer on the hole transport layer, the emission layer comprising at least a first electron transport material, a second and different electron transport material and a phosphorescent dopant, wherein the first electron transport material comprises 2,5-dispirofluorene-1,3,4-oxadiazole;

forming an electron transport layer on the emission layer;

forming an electron injection layer on the electron transport layer; and

forming a cathode on the electron injection layer.

16. The method of claim 15 , the emission layer being formed by a process selected from the group consisting of thermal evaporation, inkjet printing, and laser transferring and photolithography.

17. The method of claim 16 , the second electron transport material comprising at least one material selected from the group consisting of bis(8-hydroxyquinolato)biphenoxy metal, bis(8-hydroxyquinolato)phenoxy metal, bis(2-methyl-8-hydroxyquinolato)biphenoxy metal, bis(2-methyl-8-hydroxyquinolato)phenoxy metal, bis(2-methyl-8-quinolinolato)(para-phenyl-phenolato) metal, and bis(2-(2-hydroxyphenyl)quinolato) metal where the metal is an element selected from the group consisting of Al, Zn, Be and Ga.

18. The method of claim 17 , the phosphorescent dopant being an emission material selected from the group consisting of bisthienylpyridine acetylacetonate Iridium, bis(benzothienylpyridine)acetylacetonate Iridium, bis(2-phenylbenzothiazole)acetylacetonate Iridium, bis(1-phenylisoquinoline)Iridium acetylacetonate, tris(1-phenylisoquinoline)iridium, tris(phenylpyridine)iridium, tris(2-biphenylpyridine)iridium, tris(3-biphenyl pyridine)iridium, tris(4-biphenyl pyridine)iridium and Ir(pq) 2 (acac) where pq denotes 2-phenylquinoline and acac denotes acetylacetone.

19. The method of claim 15 , wherein the two electron transport materials have different highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels, wherein a HOMO energy level of at least one of the at least two electron transport materials is lower than a HOMO energy level of the phosphorescent dopant, and a LUMO energy level of at least one of the at least two electron transport materials is greater than a LUMO energy level of the phosphorescent dopant.