Solution-processed bipolar small molecular host materials for single-layer blue phosphorescent organic light-emitting diodes

摘要

Three new solution processable small molecular host materials based on the bis-[3,5-di(9H-carbazol-9-yl) phenyl] structural moiety have been developed for blue phosphorescent (Flrpic dopant) organic light emitting diodes. All three host materials have been characterized as having high gtass transition temperatures (T_gs), 155-175 °C, indicative of good morphological stability of their amorphous thin films prepared from the solution process. Whereas N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyllmethylamine (CzPAMe) has the highest solid state triplet energy gap (E_T) of 2.73 eV, tetrakis-[3,3',5,5'-(9H-carbazol-9-yl)]triphenylphosphine oxide (CzPPO) and N,N-bis-[3,5-di(9H-carbazol-9-yl)phenyl]pyrimidin-2-amine (CzPAPm) are two host materials which are potentially bipolar for charge transport due to the electron deficient units of phenylphosphine oxide and pyrimidine, respectively. Due to the insufficient E_T (2.56 eV) of CzPAPm, CzPPO or CzPAMe devices are significantly better than CzPAPm devices with Or without a l,3-bis[(4-fert-butylphenyl)-l,3,4-oxadiazolyl]phenylene (OXD-7) co-host. Particularly, having no OXD-7 co-host and no vacuum thermal-deposited extra electron transporting layer, single-layer devices of CzPPO surpass CzPAMe devices and reach current efficiencies as high as 9.32 cd A-1 (or power efficiency of 4.97 Im W~(-1)), one of the highest efficiencies among small molecular devices with the same fabrication process and same device configuration.