LAUSR

A high triplet energy level (ET) and balanced carrier mobility are critical factors for host materials in efficient blue phosphorescent organic light-emitting diodes (PHOLEDs). Herein, we report a facile synthesis of four compounds, dicarbazolylphenylphosphine (DCPP), dicarbazolylphenylphosphine oxide (DCPPO), tricarbazolylphosphine (TCP), and tricarbazolylphosphine oxide (TCPO), and their application as host materials in a classic blue phosphorescent emitter bis[2-(4,6-difluorophenyl)pyridinato-C2,N](picolinato)iridium(III) (FIrpic). The four compounds show a high ET of up to 3.0 eV and tunable mobilities. We fabricated four OLEDs with a device structure of ITO/MoO3 (1 nm)/N,N′-dicarbazolyl-3,5-benzene (mCP):MoO3 (20 wt%, 10 nm)/mCP (30 nm)/Host:FIrpic (7 wt%, 20 nm)/1,3,5-tri(m-pyrid-3-yl-phenyl) benzene (TmPyPB, 40 nm)/LiF (1 nm)/Al (100 nm), all of which display maximum external quantum efficiencies (EQEs) exceeding 20%. The DCPPO-based device reaches the highest EQE of 27.5%, the maximum luminance of 14 070 cd m−2, and the lowest efficiency roll-off of 22.2% from 1 to 10 mA cm−2, which is among the best-performing FIrpic-based PHOLEDs without using any light extraction method.