Polymers with alkyl main chain pendent biphenyl carbazole or triphenylamine unit as host for polymer light emitting diodes

摘要

The soluble styrene polymers, bearing dicarbazole, phenylcarbazole or phenyltriphenylamine side groups were investigated as a host material for green emitter in phosphorescent PLED devices. Those polymers were synthesized by free radical polymerization via azobisisobutyronitrile (AIBN) as initiator under 75 °C. All of the host materials exhibit high thermal stability with high decomposition (T _(d,5% weight loss) > 398 °C) and glass transition temperatures (T _g > 172 °C). The HOMO (ca. -5.39 -5.69 eV) and LUMO (ca. -2.22 -2.41 eV) levels with the triplet energy of ca. 2.50-2.93 eV suggest that polymers are suitable for host materials for green emitter. The devices based on the emissive layers containing host materials doped with Ir(ppy) _3 (4 wt%) display stable green emission with high device performances. The brightness and current efficiency reach 15,800 cd/m ~2 and 17.5 cd/A, respectively, at the optimum blending with 40 wt% 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazol (t-PBD). Furthermore, the device performance reached higher brightness (23,400 cd/m ~2) and current efficiency (12.3 cd/A) when mixture with 2,4,6-triphenyl-1,3,5-triazine (TRZ) and t-PBD.