Solution processable ionic p - i - n phosphorescent organic light-emitting diodes

We report efficient light-emission from solution-processed single-layered phosphorescent organic light-emitting diodes (PHOLEDs) that were doped with ionic salt and treated with simultaneous electrical and thermal annealing. Because the simultaneous annealing causes the adsorption of salt ions at the electrode surfaces, the energy levels of the organic molecules are bent by the electric fields due to the adsorbed ions; i.e., the annealing can induce the proper formation of an ionic p - i - n structure. As a result, an ionic p - i - n PHOLED with a peak luminescence of over ∼ 35 000 cd ∕ m 2 and a power efficiency of 42 lm ∕ W was achieved through increased and balanced carrier injections.