Charge Transport and Recombination in Polyspirobifluorene Blue Light-Emitting Diodes

The charge transport in blue light-emitting polyspirobifluorene is investigated by both steady-state current-voltage measurements and transient electroluminescence. Both measurement techniques yield consistent results and show that the hole transport is space-charge limited. The electron current is found to be governed by a high intrinsic mobility in combination with electron traps. Numerical simulations on light-emitting diodes reveal a shift in the recombination zone from the cathode to the anode with increasing bias.