The effect of energy level offset between Ir dopant and carbazole hosts on the emission efficiency

Abstract

The interface energy offsets of various carbazole hosts and iridium (III) [bis(4,6-difluorophenyl) pyridinato-N, C-2']-tetrakis(1-pyrazolyl) borate (FIr6) and their influence on the efficiency were investigated. Vacuum level shifted by +0.12 eV for bis(4-(N-carbazolyl)phenyl) dimethylsilane (Me2SiCBP2) and FIr6 interface, which was negligible for other hosts and FIr6 interface. As a result, the hole injection from the host to the guest was almost barrier free to reach a high efficiency of 17.1% in the Me2SiCBP2 based device. It dropped to 14% when N, N'-dicarbazolyl-3,5-benzene (mCP) was used as the host, which is the reminiscent of the existence of a hole injection barrier (-0.16 eV). (C) 2010 American Institute of Physics. [doi:10.1063/1.3462931]