Phosphorescent oled having double exciton-blocking layers

1. An organic light-emitting device comprising:

a. an anode;

b. a cathode;

c. a hole-transporting layer disposed between the anode and the cathode;

d. a phosphorescent light-emitting layer disposed between the hole-transporting layer and the cathode, wherein the phosphorescent light-emitting layer includes at least one host and at least one phosphorescent dopant;

e. a first exciton-blocking layer disposed between the hole-transporting layer and the phosphorescent light-emitting layer; wherein the first exciton-blocking layer includes a first exciton-blocking material that has a triplet energy greater than the triplet energy of the host in the phosphorescent light-emitting layer; and

f. a second exciton-blocking layer disposed between the first exciton-blocking layer and the phosphorescent light-emitting layer, wherein the second exciton-blocking layer is in contact with the phosphorescent light-emitting layer, and wherein the second exciton-blocking layer includes a second exciton-blocking material that has a triplet energy less than the triplet energy of the first exciton-blocking material,

wherein the first exciton-blocking material and the second exciton-blocking material are different carbazole derivatives represented by formula (J):

wherein:

n is an integer from 1 to 4;

Q is phenyl, substituted phenyl, biphenyl, substituted biphenyl, aryl, or substituted aryl group;

R 1 through R 8 are independently hydrogen, alkyl, phenyl or substituted phenyl, aryl amine, carbazole, or substituted carbazole and provided that R 1 -R 8 do not contain aromatic hydrocarbon fused rings.

2. The organic light-emitting device of claim 1 , wherein the second exciton-blocking layer enhances the exciton-blocking effect and eliminates light emission from the hole-transporting layer.

3. The organic light-emitting device of claim 1 wherein the second exciton-blocking layer has a triplet energy greater than the triplet energy of the dopant in the phosphorescent light-emitting layer.

4. The organic light-emitting device of claim 1 wherein the second exciton-blocking layer has an oxidation potential not less than the oxidation potential of the first exciton-blocking layer.

5. The organic light-emitting device of claim 1 wherein the second exciton-blocking layer has an oxidation potential less than the oxidation potential of the host in the phosphorescent light-emitting layer.

6. The organic light-emitting device of claim 1 wherein the second exciton-blocking layer has a reduction potential less than the reduction potential of the host in the phosphorescent light-emitting layer.

7. The organic light-emitting device of claim 1 wherein the first exciton-blocking layer and the second exciton-blocking layer each has a thickness in the range of from 1 nm to 50 nm.

8. The organic light-emitting device of claim 1 wherein the first exciton-blocking layer and the second exciton-blocking layer each has a thickness in the range of from 2 nm to 20 nm.

9. The organic light-emitting device of claim 1 wherein the carbazole derivative in the first exciton-blocking layer is selected from:

EXBM-1 (TCTA)

EXBM-3 (MCP)

10. The organic light-emitting device of claim 1 wherein the carbazole derivative in the second exciton-blocking layer is selected from 9,9′41,′-biphenyl]-4,4′-diylbis-9H-carbazole (CBP), 9,9′-(2,2′-dimethyl[1,1′-biphenyl]-4,4′-diyl)bis-9H-carbazole (CDBP) and 9,9′-(1,4-phenylene)bis-9H-carbazole.

11. The organic light-emitting device of claim 1 wherein the host in the phosphorescent light-emitting layer includes an electron-transporting material.

12. The organic light-emitting device of claim 11 wherein the electron-transporting materials is a benzazole derivative represented by structural formula (K):

wherein:

n is selected from 2 to 8 and i is selected from 1-5;

Z is independently O, NR or S;

R is individually hydrogen; alkyl of from 1 to 24 carbon atoms aryl or hetero-atom substituted aryl of from 5 to 20 carbon atoms, halo, or atoms necessary to complete a fused aromatic ring; and

X is a linkage unit including carbon, alkyl, aryl, substituted alkyl, or substituted aryl, which conjugately or unconjugately connects the multiple benzazoles together.

13. The organic light-emitting device of claim 12 wherein the benzazole derivative includes 2,2′,2″-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI).

14. The organic light-emitting device of claim 11 wherein the electron-transporting material is an aluminum or gallium complex represented by Formula (R-a):

wherein:

M 1 is Al or Ga; and

R 2 -R 7 independently represent hydrogen or an alkyl group; and

L is an aromatic moiety with 6 to 30 carbon atoms.

15. The organic light-emitting device of claim 14 wherein the aluminum or gallium complex includes aluminum(III) bis(2-methyl-8-hydroxyquinoline)-4-phenylphenolate [alias, Balq] and gallium oxine [alias, tris(8-quinolinolato)gallium(III).

16. The organic light-emitting device of claim 1 wherein the device includes two light-emitting layers.

17. The organic light-emitting device of claim 16 wherein the two light-emitting layers emit light of substantially different colors.

18. The OLED of claim 1 wherein the phosphorescent dopant in the phosphorescent light-emitting layer is selected from tris(1-phenylisoquinoline) iridium (III) (Ir(piq) 3 ), Ir(ppy) 2 (cou1), Ir(cou2) 2 ppy, or tris(2-phenylpyridine) iridium (III) (Ir(ppy) 3 ).

19. The organic light-emitting device of claim 1 that produces white light.