Solution-processible small-molecular host materials for high-performance phosphorescent organic light-emitting diodes

Two novel carbazole-based molecules were synthesized by attaching 3,6-bis(3,6-di-tert-butyl-carbazol-9-yl)-carbazole and pyrazole to the dimethylbiphenyl core in a symmetric and asymmetric way. Owing to highly twisted configuration, they exhibit high triplet energy of 2.90 eV. They are suitable for spin coating to make thin films. The complete spatial separation of frontier molecular orbitals and the single-carrier devices study confirm the bipolar feature of pyrazole-containing material. They were used as hosts to fabricate phosphorescent organic light-emitting diodes by wet method. The green devices exhibited maximum efficiencies of 33 cd A(-1) and 35 cd A(-1), which far exceed that (23 cd A(-1)) of the control device with the polyvinylcarbazole host. The versatility of these hosts also spread to orange devices and peak efficiencies of 35 cd A(-1) and 39 cd A(-1) were achieved. The pyrazole-containing material always performed better due to its bipolar charge transporting nature. (C) 2013 Elsevier Ltd. All rights reserved.