| abstract |
An improved OLED includies an emitter layer disposed between a cathode and an anode where the emitter layer includes a host material and a phosphorescent emitter material. A first hole transport layer is disposed between the emitter layer and the anode and a second hole transport layer is disposed between the first hole transport layer and the anode. The first hole transport layer includes a first hole transport material that is a carbazole type compound and the second hole transport layer includes a second hole transport material that is different from the first hole transport material. The phosphorescent emitter material includes a phosphorescent organometallic compound that is a heteroleptic compound represented by the formula L 2 MX, LL'MX, LL'L"M, or LMXX', wherein L, L', L", X, and X' are inequivalent, bidentate ligands and M is a metal that forms octahedral complexes, wherein L, L', and L" are monoanionic inequivalent bidentate ligands coordinated to M through an sp 2 hybridized carbon and a heteroatom. |