Phosphorescent OLED device with mixed hosts

1. An OLED device comprising a cathode, an anode, and having therebetween a light-emitting layer containing:

a) a phosphorescent emitter that emits light yellow, orange or red light,

b) a tertiary arylamine compound as a first host material, and

c) a gallium complex with only nitrogen bidentate ligands as a second host material,

the OLED device further comprising an exciton-blocking layer located directly adjacent to the light-emitting layer on the anode side,

wherein the gallium complex with only nitrogen bidentate ligands has a triplet energy at least 0.05 eV greater than the phosphorescent emitter, and

wherein the exciton-blocking layer contains at least one material with a triplet energy equal to or greater than the phosphorescent emitter.

2. An OLED device of claim 1 , wherein the first host is 60% or less by volume of the light-emitting layer.

3. An OLED device of claim 2 , wherein the phosphorescent emitter contains Iridium.

4. An OLED device of claim 3 , wherein the phosphorescent emitter emits yellow light.

5. An OLED device of claim 3 , wherein the phosphorescent emitter emits orange light.

6. An OLED device of claim 3 , wherein the phosphorescent emitter emits red light.

7. An OLED device of claim 1 , wherein the gallium complex with only nitrogen bidentate ligands is according to Formula (PH2-2):

wherein each Z a and Z b is independently selected and represents the atoms necessary to complete an unsaturated heterocyclic ring and Z a and Z b are directly bonded to one another.

8. An OLED device of claim 7 wherein each nitrogen bidentate ligand contains only nitrogen and carbon atoms.

9. An OLED device of claim 8 , wherein the gallium complex is according to Formula (PH2-3):

wherein each Z 1 through Z 7 represents N or C—Y with no more than two Z 1 —Z 7 representing N and where Y represents hydrogen or an independently selected substituent.

10. An OLED device of claim 9 , wherein no more than one Z 1 —Z 7 is N.

11. An OLED device of claim 1 , wherein the tertiary arylamine compound is represented by formula (PH1-1):

wherein each Are is an independently selected arylene group, such as a phenylene or anthracene moiety,

n is selected from 1 to 4, and

R 1 —R 4 are independently selected aryl groups.

12. An OLED device of claim 1 , wherein the tertiary arylamine compound is represented by formula (PH1-3):

wherein Q independently represents nitrogen, carbon, silicon, a substituted silicon group, an aryl group, or substituted aryl group, preferably a phenyl group;

R 1 is an aryl or substituted aryl group;

R 2 through R 7 are independently hydrogen, alkyl, phenyl or substituted phenyl group, aryl amine, carbazole, or substituted carbazole; and

n is selected from 1 to 4;

or is represented by formula (PH1-4):

wherein, n is selected from 1 to 4;

Q independently represents phenyl group, substituted phenyl group, biphenyl, substituted biphenyl group, aryl, or substituted aryl group; and

R 1 through R 6 are independently hydrogen, alkyl, phenyl or substituted phenyl, aryl amine, carbazole, or substituted carbazole.

13. An OLED device of claim 1 where the tertiary arylamine first host has a triplet energy equal to or greater than the phosphorescent emitter.

14. An OLED device of claim 1 including on the cathode side of the light-emitting layer, an adjacent non-luminescent blocking layer in direct contact with the light-emitting layer, and an adjacent electron transporting layer structure in direct contact with the non-luminescent blocking layer.

15. An OLED device of claim 14 wherein the non-luminescent blocking layer contains a material with a HOMO at least 0.2 eV more negative than the HOMO of the tertiary arylamine compound in the light-emitting layer.

16. An OLED device of claim 14 wherein the non-luminescent blocking layer contains a material with a HOMO at least 0.2 eV more negative than the HOMO of the phosphorescent emitter in the light-emitting layer.