| abstract |
Organic light emitting materials and devices comprising phosphorescent metal complexes comprising ligands comprising aryl or heteroaryl groups substituted at both ortho positions are described. An organic light emitting device, comprising: an anode, a hole transport layer; an organic emissive layer comprising an emissive layer host and an emissive dopant; an electron impeding layer; and electron transport layer; and a cathode disposed, in that order, over a substrate. |