Cascade energy transfer in dye-doped ternary polymer blend light-emitting diodes

We report the realization of efficient and color-variable organic electroluminescent (EL) devices which employ the cascade energy transfer in a dye-doped ternary polymer blend. Fluorene-based light-emitting polymers, poly(2,7-bis(p-stiryl)-9,9′-di-n-hexylfluorene sebacate) (PBSDHFS) and poly(9,9′-di-n-hexylfluorenediylvinylene-alt-1,4-phenylenevinylene) (PDHFPPV), and a laser dye, DCM were used for this study. Förster excitation energy transfer in the PBSDHFS/PDHFPPV (98w/2w), PDHFPPV/DCM (98w/2w), PBSDHFS/DCM (98w/2w), and PBSDHFS/PDHFPPV/DCM (98w/2w/2w) blend played an essential role in achieving color-tunability as well as high efficiency due to the reduced self-absorption loss and concentration quenching. The EL device made of the PBSDHFS/PDHFPPV/DCM (98w/2w/2w) blend showed the highest EL quantum efficiency (QE). We attribute this result to an effective carrier trapping capability of DCM as well as the excitation energy transfer.