Time delayed collection field experiments on polymer: fullerene bulk-heterojunction solar cells

The recombination of photogenerated charge carriers in poly[2-methoxy-5-(3,7-dimethyloctyloxy)-1,4-phenylene vinylene]:1-(3-methoxycarbonyl)-propyl-1-phenyl-[6,6]C61 bulk-heterojunction solar cells is investigated using the time delayed collection field technique. Here the lifetime of photogenerated electrons and holes that have escaped charge recombination can be determined from current measurements using a pulsed collection voltage that is delayed with respect to the excitation pulse. At 80 K, the number of long lived charge carriers decays in time according to t– with =0.2, practically independent of laser fluence in the range of 1–1000 µJ/cm2. For excitation densit