Self-trapping mechanism in green phosphorescent dye-doped polymer light-emitting diodes

Abstract

The mechanism for exciting electroluminescence (EL) in a green phosphorescent dye, iridium(III)tris(2-(4-tolyl)pyridinato-N,C2) (Ir(mppy)3), doped in a host blue-emitting conducting polymer, poly[9,9-di-n-hexyl-fluorenyl-2,7-diyl] (PFO), has been studied. Photoluminescence measurements have been made on PFO/Ir(mppy)3 (0–12%) composites to rule out the possibility of singlet exciton energy transfer from the host polymer to the green dye. EL measurements have also been made to study the behavior of the composites in the presence of dc bias. The dominant mechanism for energy transfer from PFO to Ir(mppy)3 is found to be self-trapping of the charge carriers in the dye molecules, due to the extremely low LUMO and high HOMO levels as compared with PFO, thereby producing EL in the green region.