Solution-processed blue phosphorescent OLEDs with carbazole-based polymeric host materials

Abstract

A new carbazole-based polymer PEPEK varying from the previously reported PEPK by the length of the spacer between the polymer backbone and the pendent carbazole moiety was investigated as polymeric host for solution-processed devices. Interestingly, if the two polymers are structurally close since the length of the alkyl chain only differs from one carbon atom, the previously reported PEPK gave higher performances than the newly synthesized PEPEK when tested as host for the wide bandgap triplet emitter FIrpic. To optimize electroluminescence performances, two device configurations were examined. On doping the emissive layer of phosphorescent organic light-emitting devices (OLEDs) at 16wt% with FIrpic, best PEPK-based OLEDs gave an efficacy of 15.14cd/A whereas PEPEK-based devices furnished an efficiency of 12.17cd/A in the same conditions. To determine the origin of this unexpected behavior, the new polymer PEPEK was characterized by UV–visible absorption and luminescence spectroscopy as well as cyclic voltammetry. Thermal properties of PEPEK were also examined and compared to those of PEPK.