Editors : Y. Lu, J.M. Merrill, M.T. Lusk, S. Bailey, A. Franceschetti
a1 Department of Electrical and Computer Engineering, University of Virginia, 351 McCormick Road, Charlottesville, VA 22904, U.S.A
a2 Department of Chemistry, University of Southern California, 837 Bloom Walk, Los Angeles, CA 90089, U.S.A
A transient response technique has been employed to investigate the lifetime of free polarons in bulk heterojunction blends of regioregular poly (3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61 butyric acid methylester (PCBM) at different annealing temperatures. Device efficiency and charge mobility were also measured. The longest lifetime, ∼ 1.5 microseceonds, was achieved for an annealing temperature of 140˚C; this represents a 2.5 x increase in lifetime relative to unannealed samples. The 140˚C annealing temperature also yields the highest efficiency. These measurements provide an estimate of the mobility-lifetime product, a figure of merit for charge transport in organic bulk heterojunctions.