Click'' Synthesis of a Bipolar Dendrimer as a Host Material for Electrophosphorescent Devices

A new solution-processable bipolar dendrimer with carbazole units as hole-transporting units and oxadiazole units as electron-transporting units was efficiently synthesized based on a convergent approach by alternation of a Cu-catalyzed azide/alkyne cycloaddition reaction and Williamson ether synthesis. The orthogonal chemistry completely avoided protection and activation of the focal points in the process of dendrimer synthesis. The dendrimer showed a wide bandgap and good thermal stability. Electrophosphorescent devices with the configuration ITO/PEDOT:PSS/bipolar dendrimer: Ir(ppy)(3)/TPBI/LiF/Al were fabricated. The devices showed a maximum current efficiency of 16.8 cd.A(-1), a maximum power efficiency of 4.22 lm.W-1 and an external quantum efficiency of 5.7%.