High-efficiency and low-voltage p-i-n electrophosphorescent organic light-emitting diodes with double-emission layers

We demonstrate high-efficiency organic light-emitting diodes by incorporating a double-emission layer (D-EML) into $p\text{‐}i\text{‐}n$ -type cell architecture. The D-EML is comprised of two layers with ambipolar transport characteristics, both doped with the green phosphorescent dye tris(phenylpyridine)iridium. The D-EML system of two bipolar layers leads to an expansion of the exciton generation region. Due to its self-balancing character, accumulation of charge carriers at the outer interfaces is avoided. Thus, a power efficiency of approximately 77 lm∕W and an external quantum efficiency of 19.3% are achieved at $100\mathrm{cd}∕{\mathrm{m}}^2$ with an operating voltage of only 2.65 V. More importantly, the efficiency decays only weakly with increasing brightness, and a power efficiency of 50 lm∕W is still obtained even at $4000\mathrm{cd}∕{\mathrm{m}}^2$ .