High-efficiency organic electrophosphorescent devices with tris(2-phenylpyridine)iridium doped into electron-transporting materials

We demonstrate high-efficiency organic light-emitting devices employing the green electrophosphorescent molecule, fac tris(2-phenylpyridine)iridium [I r(ppy)(3)], doped into various electron-transport layer (ETL) hosts. Using 3-phenyl-4-(1'-naphthyl)-5-phenyl-1,2,4-triazole as the host, a maximum ext ernal quantum efficiency (eta(ext)) of 15.4 +/- 0.2% and a luminous power e fficiency of 40 +/- 2 Im/W are achieved. We show that very high internal qu antum efficiencies (approaching 100%) are achieved for organic phosphors wi th low photoluminescence efficiencies due to fundamental differences in the relationship between electroluminescence from triplet and singlet excitons . Based on the performance characteristics of single and double heterostruc tures, we conclude that exciton formation in Ir(ppy)(3) occurs within close proximity to the hole-transport layer/ETL:Ir(ppy)(3) interface. (C) 2000 A merican Institute of Physics. [S0003-6951(00)00332-6].