Organic electroluminescent devices with additive

1. An electroluminescent device comprising a cathode and an anode and, located therebetween, a light-emitting layer (LEL) and a hole transporting layer between the LEL and the anode, the LEL comprising a phosphorescent guest material, a hole- and electron-transporting host material, and an efficiency-enhancing material, wherein the triplet energy of the phosphorescent guest material is lower than that of the host, wherein the efficiency-enhancing material is present in an amount (1 to 30 wt. % of the LEL) that is sufficient to provide an increase in luminous yield compared to no enhancing material, has an ionization potential lower than that of the host material and, has a triplet energy level that is higher than that of the phosphorescent guest material.

2. The device of claim 1 wherein the efficiency-enhancing material is not emissive.

3. The device of claim 1 wherein the phosphorescent guest material emits green light.

4. The device of claim 1 wherein the phosphorescent guest material emits red light.

5. The device of claim 1 wherein the phosphorescent guest material is an organometallic compound comprising a 5th-row transition metal.

6. The device of claim 1 wherein the metal is iridium or platinum.

7. The device of claim 1 wherein the organometallic compound includes a ligand that can be coordinated to a metal through an sp 2 carbon and a heteroatom.

8. The device of claim 7 wherein the ligand is a phenylpyridine group.

9. The device of claim 5 wherein the organometallic compound is chosen from tris(2-phenylpyridinato-N,C 2′ )iridium(III)), bis(2-phenylpyridinato-N,C 2′ )iridium(III)(acetylacetonate), bis(2-phenylpyridinato-N,C 2′ )platinum(II), tris(2-phenylquinolinato-N,C 2′ ) iridium(III), tris(1-phenylisoquinolinato-N,C 2′ )iridium(III), and tris(3-phenylisoquinolinato-N,C 2′ )iridium(III) groups.

10. The device of claim 1 wherein the efficiency-enhancing material is present at a concentration of 3 to 10% by weight of the light-emitting layer.

11. The device of claim 1 wherein the phosphorescent guest material is present at a concentration of 1 to 20% by weight of the light-emitting layer.

12. The device of claim 1 wherein the phosphorescent guest material is present at a concentration of 3 to 10% by weight of the light-emitting layer.

13. The device of claim 1 wherein the efficiency-enhancing material is a tertiary aromatic amine.

14. The device of claim 13 wherein the efficiency-enhancing material includes two or more triarylamine groups linked together by a linking group.

15. The device of claim 1 wherein the efficiency-enhancing material is a compound represented by Formula (2a),

wherein:

R 1 and R 2 represent hydrogen or substituents, provided R 1 and R 2 can join to form a ring;

Ar 1 -Ar 4 represent independently selected aromatic groups;

each R a independently represents hydrogen or an independently selected substituent; and

each n is independently selected as 0-4.

16. The device of claim 1 wherein the efficiency-enhancing material is a compound represented by Formula (2b),

wherein:

Ar 5 -Ar 10 independently represent aromatic groups;

each R b independently represents an independently selected substituent; and

each m is independently selected as 0-4.

17. The device of claim 1 wherein the efficiency-enhancing material is chosen from:

1,1-Bis(4-di-p-tolylaminophenyl)cyclohexane;

1,1-Bis(4-di-p-tolylaminophenyl)-4-phenylcyclohexane;

1,1-Bis(4-di-p-tolylaminophenyl)-4-methylcyclohexane;

1,1-Bis(4-di-p-tolylaminophenyl)-3-phenylpropane;

4,4′,4″-Tris(diphenylamino)triphenylamine;

4,4′,4″-Tris[(3-methylphenyl)phenylamino]triphenylamine;

Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)methane;

Bis[4-(N,N-diethylamino)-2-methylphenyl](4-methylphenyl)ethane;

4-(4-Diethylaminophenyl)triphenylmethane; and

4,4′-Bis(4-diethylaminophenyl)diphenylmethane.

18. The device of claim 1 wherein the host material comprises a compound selected from arylamine, triazole, indole, and carbazole group containing compounds.

19. The device of claim 1 wherein the host material comprises a carbazole represented by Formula 1:

wherein:

W independently represents hydrogen or an independently selected substituent, p independently is 0-4, and L A represents a linking group.

20. The device of claim 1 wherein the host material comprises one selected from 4,4′-N,N′-dicarbazole-biphenyl, 4,4′-N,N′-dicarbazole-2,2′-dimethyl-biphenyl, 1,3-bis(N,N′-dicarbazole)benzene, and poly(N-vinylcarbazole) group containing compounds.

21. The device of claim 1 that comprises two or more host materials.

22. The device of claim 1 including a means for emitting white light.

23. The device of claim 22 including two or more compounds capable of emitting complimentary colors.

24. The device of claim 22 including a compound capable of emitting white light.

25. The device of claim 22 including a filtering means.

26. A display comprising the electroluminescent device of claim 1 .

27. An area lighting device comprising the electroluminescent device of claim 1 .

28. A process for emitting light comprising applying a potential across the device of claim 1 .