Balancing charge carrier mobility by constructing chemical structures to contain both hole- and electron-transporting moieties in electroluminescent organic compounds

For the purpose of balancing charge carriers' transport, we designed and synthesized two new compounds that are composed of both electron- and hole-transporting structural moieties: electron-transporting moieties are diaryl-1,3,4-oxadizole (Oxa) groups and hole transport moieties carbazole (Cz), or triphenylamine (TPA) moieties. The compounds formed amorphous glassy films when vacuum deposited and their glass transition temperature (Tg) was close to or higher than 150 °C. Their electronic structures (the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO), and Eg values) and hole and electron mobilities in the compounds were studied. A couple of compounds bearing oxadiazole moieties revealed the electron mobility greater than 1.0 × 10−4 cm2/(V s) at the electric field of 7.5 × 105 V/cm. The single layer light-emitting electroluminescence (EL) devices show that the external quantum efficiencies of the devices fabricated with those compounds having balanced carrier mobilities are much higher than those of the compounds composed of predominantly hole- or electron-transporting moieties.