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 $[Ir(ppy)3],$ 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 external quantum efficiency $(ηext)$ of $15.4±0.2%$ and a luminous power efficiency of $40±2 Im/W$ are achieved. We show that very high internal quantum efficiencies (approaching 100%) are achieved for organic phosphors with 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 heterostructures, we conclude that exciton formation in $Ir(ppy)3$ occurs within close proximity to the $hole-transport layer/ETL:Ir(ppy)3$ interface.