Soluble polynorbornenes with pendant carbazole derivatives as host materials for highly efficient blue phosphorescent organic light-emitting diodes

摘要

We report novel host polymers for a high-efficiency polymer-based solution-processed phosphorescent organic light-emitting diode with typical blue-emitting dopant bis(4,6-difluorophenylpyridinato-N,C ~2) iridium(III) picolinate (FIrpic). The host polymers, soluble polynorbornenes with pendant carbazole derivatives, N-phenyl-9H-carbazole (P1), N-biphenyl-9H-carbazole (P2), and 9,9'-(1,3-phenylene)bis-9H-carbazole (mCP) (P3) are efficiently synthesized by vinyl addition polymerization of norbornene monomers using Pd(II) catalyst in combination with 1-octene chain transfer agent. The polymers exhibit high thermal stability with high decomposition (T _(d5) > 410 °C) and glass transition temperatures (T _g ≈ 268 °C). The HOMO (ca. -5.5 to -5.7 eV) and LUMO (ca. -2.0 to -2.1 eV) levels with the high triplet energy of about 2.7-3.0 eV suggest that the polymers are suitable for a host material for blue emitters. Among the solution-processed devices that were fabricated based on the emissive layers containing the P1-P3 host doped with various concentrations of FIrpic (7-13 wt %), the best device with P3 host exhibits power efficiency of 3.0 lm W ~(-1) and external quantum efficiency of 4.0% at a luminance of 1000 cd m ~(-2) that is outstanding among the polymeric rivals.