A phosphorescent OLED uses a phosphorescent dopant in the emissive layer, the dopant includes a metal complex containing a plurality of moieties linking to a transition metal ion. One or more of the moieties contain a ligand with a C--SP.sup.3 carbon center. The transition metal ion can be an iridium ion. The C--SP.sup.3 carbon is linked to a chalcogen atom in an ion form, a nitrogen-containing heterocylic ring and two functional groups, wherein each of the functional groups is selected from aryl, alkyl and heteroaryl. The tetrahedral structure of this carbon center hinders close packing and intermolecular interactions and, therefore, renders the transport of holes in the light-emitting device more efficient. With such chemical structure and property, the self-quenching characteristics of the dopant in high doping concentration can be effectively reduced.