Green organic light-emitting diodes with high power efficiency by constructing well-matched device structure to low down operation voltage

A series of green organic light-emitting diodes (OLEDs) were fabricated and investigated based on well-known emitter Tris(2-phenylpyridine)iridium(III) (Ir(mppy)3). To low down operation voltage, 4,4′,4″-Tri(9-carbazoyl) triphenylamine (TcTa) and 4,7-dicarbazol-9-yl-[1,10]-phenanthroline (BUPH1) were selected as the host materials of light-emitting layers (EMLs) 1 and 2, respectively, because of well-matched energy levels and high carrier mobilities. In addition, well-matched device structure helps to broaden recombination zone, thus suppressing the roll-off of electroluminescent (EL) efficiencies. To balance the distribution of holes and electrons within recombination zone, emitter concentrations and EMLs thicknesses were optimized detail by detail. Finally, the optimal green OLED obtained the brightness of 113,374 cd m−2, current efficiency of 85.56 cd A−1, power efficiency of 111.94 l m W−1 and external quantum efficiency (EQE) of 22.7%. At 1000 cd m−2 (3.1 V), which is a key brightness, power efficiency as high as 68.86 l m·W−1 can still be retained due to low operation voltage.