We report on the spectroscopic, electrochemical, and electroluminescent properties of [Ir(ppy)(2)-(dtb-bpy)](+)(PF6)(-) (ppy: 2-phenylpyridine, dtb-bpy: 4,4'-di-tert-butyl-2,2'-dipyridyl). Single-layer devices were fabricated and found to emit yellow light with a brightness that exceeds 300 cd/m(2) and a luminous power efficiency that exceeds 10 Lm/W at just 3 V. The PF6- space charge was found to dominate the device characteristics.