Patent ID: 7674531

Claim:
An organic light emitting device comprising an anode, a cathode and an emissive layer, wherein the emissive layer is located between the anode and the cathode and the emissive layer comprises an electron transporting host material doped with a phosphorescent dopant material, wherein the phosphorescent dopant material has a HOMO energy less than the ionization potential of the electron transporting host material, wherein the phosphorescent dopant material has a LUMO energy level lower than a LUMO energy level of the electron transporting host material, wherein the electron transporting host material has a lowest triplet excited state having a triplet state energy, wherein the phosphorescent dopant material has a triplet excited state with a triplet state energy that is less than the triplet state energy of the lowest triplet excited state of the electron transporting host material, and wherein the phosphorescent dopant material is a phosphorescent organometallic complex comprising a metal species M with a bidentate mono-anionic ligand in which M is coordinated with an sp 2 hybridized carbon and a heteroatom of the ligand.