Ultrafast electron transfer and decay dynamics in a small band gap bulk heterojunction material

Photoinduced electron transfer in a small band gap bulk heterojunction material (see figure) is studied by ultrafast spectroscopic methods. In this composite, the photo excitation initiates ultrafast electron transfer from the polymer to the fullerene, as in most bulk heterojunction materials. From analysis of the carrier recombination dynamics, we infer the existence of an intermediate charge transferred state from which long-lived mobile positive and negative carriers are generated.