Acceptor Energy Offset Manages Ultrafast Recombination Dynamics in Donor-Acceptor Mixtures

Abstract

We study charge recombination rates in blends of MEH-PPV and a comprehensive set of low molecular-weight fluorine-based acceptors, using visible-pump - IR-probe photoinduced absorption technique. The positions of acceptor’s HOMO-LUMO levels are engineered by addition of different chemical substituents. The results clearly show the exponential scaling of the charge recombination rate with the acceptor LUMO energy. The minimal donor-acceptor LUMO energy difference required to form a CTC state is estimated as ∼ 0.25 eV.