Solution-Processible Bipolar Triphenylamine-Benzimidazole Derivatives for Highly Efficient Single-Layer Organic Light-Emitting Diodes

Two solution-processible bipolar molecules, tris(3′-(1-phenyl-1 H -benzimidazol-2-yl)biphenyl-4-yl)amine (TBBI) and tris(2-methyl-3′-(1-phenyl-1 H -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 °C, and the decomposition temperatures ( T d ) of 552 and 515 °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.