Improved hole-transporting properties of Ir complex-doped organic layer for high-efficiency organic light-emitting diodes

摘要

We have investigated the hole-transporting properties of three different Ir complexes doped 4,4',4"-tri (N-carbazolyl) triphenylamine (TCTA) using a series of hole-only devices. The improvement of hole-transporting ability was depended on the species of Ir complexes and their doping concentrations. We attributed the improved performance to their strong electron-accepting abilities or hole-transfer capabilities. Yellow organic light-emitting diodes (OLEDs) based on bis(2-phenylbenzothiazolato)(acetylacetonate)iridium bt_2Ir(acac) were fabricated by utilizing this method with optimized doping concentration. The best electroluminescent (EL) performance of maximum 83.6 lm/W was obtained for the yellow-ing-emitting OLED by doping of Firpic into TCTA hole transport layer, compared with the cases of doping of Ir(ppy)_3 into TCTA and doping of Ir(bpiq)_2acac into TCTA. Moreover, the turn-on voltage of device decreased to 2.2 V, which was corresponding to the optical band gap of the emitter.