Star-Shaped Boron-Containing Asymmetric Host Materials for Solution-Processable Phosphorescent Organic Light-Emitting Diodes

Boron-containing compounds have attracted considerable attention because of their electron-accepting properties, and they are widely used in a variety of fields. However, due to the essential requirement to protect the empty p_z-orbital of the boron atom using large steric hindrance or rigid groups, borane derivatives generally show poor solubility and are rarely reported as acceptor units to construct bipolar host materials for phosphorescent organic light-emitting diodes (PhOLEDs). Here, a combined star-shaped and asymmetric donor–acceptor molecular design strategy to improve the solubility and fine tune the optical and electronic properties of boron-containing materials is presented. High thermal stability, solvent solubility, solution processability, and triplet energy are achieved simultaneously. With the thus-designed boron-containing bipolar molecules as host materials, the solution-processed PhOLEDs exhibit high device performances, which are comparable to the vacuum-processed counterparts, showing high external quantum efficiencies up to 18.5% and 14.5% in blue and white PhOLEDs, respectively. These results demonstrate the great potential of the star-shaped and symmetry-breaking borane derivatives in solution-processable organic optoelectronic devices.