Solution-processible bipolar triphenylamine-benzimidazole derivatives for highly efficient single-layer organic light-emitting diodes

Two solution-processible bipolar molecules, tris(3'-(1-phenyl-1H-benzimidazol-2-yl)biphenyl-4-yl)amine (TBBI) and tris(2-methyl-3'-(1-phenyl-1H-benzimidazol-2-yl)biphenyl-4-yl)amine (Me-TBBI), bearing both hole-transporting triphenylamine and electron-transporting benzimidazole moieties were newly prepared. TBBI and Me-TBBI possess excellent thermal stability with high glass-transition temperature (T-g) of 148 and 144 degrees C, and the decomposition temperatures (T-d) of 552 and 515 degrees C in nitrogen, respectively. They exhibit good solubility in common solvents due to the metastructured and star-shaped configuration allowing a solution processing. TBBI and Me-TBBI were employed to fabricate phosphorescent organic light-emitting diodes (OLEDs) as the host materials doped with the guest of Ir(ppy)(3) by spin coating with a single-layer structure. The solution-processed Me-TBBI device exhibited an improved performance relative to TBBI arising from the complete charge localization of HOMO and LUMO and an increase in the singlet-triplet (S-0-T-1) energy gap. The performance of spin-coated Me-TBBI device (16400 cd m(-2), 27.4 cd A(-1), 4.5 lm W-1) is outstanding with respect to other work for fully solution-processed OLEDs with the similar single-layer structure.