LEPR spectroscopy of charge carriers photoinduced in polymer/fullerene composites pp.417-446
Authors: (V.I. Krinichnyi, Institute of Problems of Chemical Physics RAS, Russia)
Abstract: Composites of conjugated polymers with fullerenes are perspective materials for plastic photovoltaics. In the present Chapter, the Light-Induced EPR (LEPR) study of magnetic, relaxation and dynamic parameters of polaron-fullerene radical pairs photoinduced in bulk heterojunction of various polymer/fullerene composites is described. Weak interaction of positively charged polarons and negatively charged fullerene anion radicals in these radical pairs was shown to stipulate by a difference interaction of charge carriers with own microenvironment. Paramagnetic susceptibility of these radicals reflects their activation dynamics and exchange interaction in the polymer/fullerene system. A decay of long-living spin pairs depends on the spatial distance between photoinduced charge carriers and on the energy of exciting photons. Microwave steady-state saturation method allowed to determine separately all relaxation and dynamics parameters for both type of charge carriers. 1D polaron diffusion along a polymer chain and fullerene pseudorotation near own main molecular axis was shown to follow activation Elliot hopping model and to be governed by photon energy. The energy required for activation of polaron diffusion differs from that of fullerene pseudorotation that proves a noninteracting character of charge carriers photoinduced in polymer/fullerene composites. Main magnetic, relaxation and dynamics parameters of these charge carriers are governed by the photon energy due inhomogeneity of distribution of polymer and fullerene domains in the composite.