Spiro-annulated hole-transport material outperforms NPB with higher mobility and stability in organic light-emitting diodes

A novel multifunctional spiro-annulated fluorene/triarylamine based compound (STNPB) has been designed, synthesized and characterized. It exhibits a high glass transition temperature of 140 °C, due to the rigid spiro-configuration molecular structure. According to its suitable energy level and triplet energy (2.34 eV), improved performances, such as lower driving voltage, enhanced device power efficiency, and longer stability, are shown in organic light-emitting diodes with STNPB as the hole-transport material, compared with the ones with the widely used arylamine derivative N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine (NPB). Through further studies, it has been demonstrated that the enhanced stability is attributed to suppressed crystallization process as a result of employing STNPB instead of NPB as the hole-transport material.