Effects of polymer sidebranching in double- and single-layer polyfluorene light-emitting diodes

We study how changes in sidebranching in electroluminescent polymers affect the performance of polyfluorene-based light- emitting diodes with and without additional hole transport materials. We observe that light emission and device efficiency are determined more by the position of the exciton recombination zone than by changes in the polymer morphology induced by sidebranching. Consequently, we find that sidebranching mainly controls the relative emission between vibrational energy levels and has a minimal effect on polymer charge transport properties. Light outputs of 10 000 cd/m(2) and device efficiencies of 0.85 and 1.8 cd/A are obtained for single- and double-layer devices, respectively. (C) 2002 American Institute of Physics