Use of cross-linkable polyfluorene in the fabrication of multilayer polyfluorene-based light-emitting diodes with improved efficiency

The authors report the use of a cross-linkable polyfluorene to fabricate multilayer light-emitting diodes (LEDs), thereby avoiding the restriction to combine polymeric solutions in different solvents. In particular, we find that for LEDs fabricated with a hole-injection layer of poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT), with magnesium cathodes and with poly(9,9-dioctylfluorene-alt-benzothiadiazole) (F8BT), as emissive layer, its electroluminescence efficiency increases from 2 to 5.5 cd/A upon insertion of the cross-linked polyfluorene between PEDOT and F8BT. This efficiency increase is attributed to an improvement of charge carrier balance within the F8BT emissive layer and a reduction of exciton quenching at PEDOT interface. (c) 2006 American Institute of Physics.