Patent ID: 7597967

Claim:
An OLED device comprising a cathode, an anode, and located therebetween a light emitting layer (LEL) comprising: a phosphorescent compound of Ir or Pt represented by the formula: wherein: A is a substituted or unsubstituted heterocyclic ring containing at least one N atom; B is a substituted or unsubstituted aromatic or heteroaromatic ring or a ring containing a vinyl C bonded to M; X-Y is an anionic bidentate ligand; and either m is an integer from 1 to 3, and n in an integer from 0 to 2 such that m+n =3 for M=Ir or m is an integer from 1 to 2 and n in an integer from 0 to 1 such that m+n=2 for M=Pt; with at least one hole transporting co-host and at least one electron transporting co-host wherein the hole transporting co-host is a substituted triarylamine with two or more triarylamine groups and no aromatic hydrocarbon fused-rings and is present at a concentration of 5 to 70 weight % of the total of the hole- and electron transporting co-host materials in the light emitting layer and wherein the triplet energy of each of the co-host materials is greater than the triplet energy of the phosphorescent emitter; and wherein the electron transporting co-host is represented by the formula: wherein: R 1 -R 8 are independently hydrogen, alkyl, aryl or substituted aryl, and at least one of R 1 -R 8 is aryl or substituted aryl; and an exciton blocking layer adjacent the emitting layer on the anode side comprising a hole transporting material with triplet energy greater or equal to 2.5 eV; and a layer directly adjacent the light emitting layer on the cathode side comprising an electron transporting material with triplet energy greater than the phosphorescent emitter.