Highly efficient, single-layer organic light-emitting devices based on a graded-composition emissive layer

We demonstrate highly efficient electrophosphorescence from devices comprising a single organic layer. High efficiency is realized by combining both hole- and electron-transporting host materials (HTMs and ETMs, respectively) into a single, graded-composition emissive layer with the green phosphorescent emitter fac-tris(2-phenylpyridine) iridium (III). The composition is continuously graded to realize nearly 100% HTM at the anode and nearly 100% ETM at the cathode. Peak external quantum and power efficiencies of ηEQE=(19.3±0.4)% and ηP=(66.5±1.3) lm/W are realized at a luminance level of 600 cd/m2.