Highly efficient phosphorescent organic light-emitting diodes based on single-layer structure

We demonstrated highly efficient single-layer organic light-emitting diodes (OLEDs) based on graded-composition architecture. The single-layer OLEDs comprise graded-composition from a mostly hole-transport material at anode to a mostly electron-transport material at cathode. The resulting device with low turn-on voltage of 2.85 V shows maximum power efficiency and current efficiency of 44.8 lm/W and 42.7 cd/A, respectively. It is found that the emission dopant plays an important role to obtain more balanced charge carriers, causing the recombination zone slightly shift to the center of the device. The results of our work suggest that the graded-composition structure represents a path to achieving highly efficient single-layer OLEDs.