Modified 4,4′,4″-Tri(N-carbazolyl)triphenylamine as a Versatile Bipolar Host for Highly Efficient Blue, Orange, and White Organic Light-Emitting Diodes

Abstract

The hole-transporting material 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) is widely used as a host in phosphorescent organic light-emitting diodes (PhOLEDs). Based on the unipolar TCTA, we synthesized a novel bipolar host material, (9-(4-(bis(4-(9H-carbazol-9-yl)phenyl)amino)phenyl)-9H-carbazol-3-yl) diphenylphosphine oxide (TCTAPO) by directly imparting an electron-transporting diphenylphosphine oxide moiety to TCTA. It was found that TCTAPO can be used as an ideal versatile host for blue, orange, and white PhOLEDs due to its high triplet energy (ET = 2.83 eV), high glass transition temperature (Tg = 165 °C), and bipolar charge-transporting ability. The maximum power efficiencies of 40.7 and 43.7 lm/W were achieved in the blue and orange PhOLEDs with FIrpic and (fbi)2Ir(acac) as the blue and orange dopants, respectively. Furthermore, the single-emitting-layer white organic light-emitting diode (WOLED) based on the emitter of TCTAPO:FIrpic:(fbi)2Ir(acac) exhibited a maximum current efficiency of 43.7 cd/A, a maximum power efficiency of 47.0 lm/W, and a maximum external quantum efficiency (ηext) of 17.2%. Compared to the PhOLEDs with TCTA as the host, the maximum power efficiencies increased about 56%, 36%, and 81%, for blue, orange, and white devices, respectively.