Triptycene derivatives as high-Tghost materials for various electrophosphorescent devices

Abstract

We have synthesized three triptycene derivatives, TCTP (2,6,14-triscarbazolyltriptycene), TATP (2,6,14-tris-(diphenylamino)triptycene) and TPOTP (2,6,14-tris(diphenylphosphoryl)triptycene) which show very high triplet energy gaps (2.94–3.15 eV) and glass transition temperatures (T_gs) ≧ 170 °C. The HOMO and LUMO levels of these three materials indicate that TCTP and TATP possess hole transport characteristics, while TPOTP has electron transport characteristics. These carrier-transporting properties are further supported by the current density–voltage characteristics of the hole-only and electron-only devices of the materials. TATP could be employed as a general host for blue, green and red electrophosphorescence devices providing high brightness, and good current and power efficiencies. The devices using TCTP and TPOTP as the host for the phosphorescence emitter FIrpic showed maximum external quantum efficiencies as high as 10.1% and 16.9%, respectively. By using a blend of TCTP and TPOTP as blue co-host for FIrpic (iridium(III) bis(4,6-difluorophenylpyridinato)picolinate), the device shows an external quantum efficiency of 15.5% at 4.5 V, current efficiency (η_c) of 31.9 cd A⁻¹ at 4.5 V, power efficiency (η_p) of 25.1 lm/W at 4.0 V, respectively. The co-host system greatly improves the performance of the device at normal operation brightness due to the decrease of driving voltage and the balance of hole and electron transport in the device.