Eric Bittner, John and Rebecca Moores Professor, Department of Chemistry, University of Houston, Houston, Texas 77204-5003, USA
We present an exciton/lattice model of the electronic dynamics of primary photoexcitations in a polymeric semiconductor heterojunction which includes both polymer π-stacking, energetic disorder, and phonon relaxation. Results from our model are consistent with a wide range of recent exper- imental evidence that excitons decay directly to well-defined polarons on a sub-100 fs timescale, which is substantially faster than exciton relaxation processes. Averaging over multiple samples, we find that as the interfacial offset is increased, a substantial fraction of the density of electronic states in the energy region about the initial exciton carries significant charge-transfer character with two charges separated in the outer regions of the model lattice. The results indicate a slight increase in the density of such current-producing states if the region close to the interface is more disordered. However, since their density of states overlaps the excitation line-shape of the primary exciton, we show that it is possible that the exciton can decay directly into current-producing states via tunneling on an ultrafast time-scale. We find this process to be independent of the location of energetic disorder in the system, and hence we expect exciton fission via resonant tunnelling to be a ubiquitous feature of these systems.
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Cette conférence est présentée par le RQMP Versant Nord du Département de physique de l'Université de Montréal et le Département de génie physique de Polytechnique Montréal.
