Excitation energy transfer and spatial exciton confinement in polyfluorene blends for application in light-emitting diodes

Abstract

We present picosecond time-resolved studies of thin films of two polyfluorene blends, combining a relatively high energy-gap poly(9,9-dioctylfluorene), PFO, and a polyfluorene derivative with a smaller gap. These studies show both efficient energy transfer from the donor to the acceptor, as well as spatial confinement of the excitons in the acceptor polymers. The optoelectronic characteristics of light-emitting diodes fabricated with such blends reflect the contribution of these two processes. The electroluminescence is almost exclusively from the acceptor polyfluorenes and we observe a significant improvement of the electroluminescence efficiency of the light-emitting diodes fabricated with such blends in comparison to those based on neat films of the polyfluorenes.