Enhanced electrophosphorescence via highly efficient energy transfer from conjugated polymer

We have demonstrated that efficient green electrophosphorescence is obtained via cascade energy transfer from poly(N-vinylearbazole) (PVK) and host fluorescent polymer to the phosphorescent iridium complex. Efficient energy transfers from PVK to fluorescent polymer and then from this host polymer to iridium complex, fac-tris[2-(2-pyridinyl-kN)[5-(2,5-dimethylphenyl)phenyl]-kC]-iridium(III) [Ir(PDPP)(3)], were observed in the PVK/fluorescent polymer/Ir(PDPP)(3) blend system, even though the chemical compatibility between this fluorescent polymer and Ir(PDPP)(3) is very poor. The phase separation between the host polymer and Ir(PDPP)(3) was restrained and highly efficient energy transfer also occurred by blending with PVK which has the good chemical compatibility with both host and guest materials. The resulting device (indium tin oxide/PEDOT/blend layer/BCP/Li:Al alloy) reaches a maximum external quantum efficiency of 8.9% and a luminous efficiency of 32 cd/A. (c) 2005 American Institute of Physics.