Light-induced ESR studies in conjugated polymer-fullerene composites

In this contribution we discuss photo-induced electron transfer in conjugat ed polymer/fullerene composites and compare this with light induced effects in pure components. Two overlapping LESR lines are observed, from positive polarons on the polymer chains and negative charges on the fullerene moiet ies. Microwave power saturation studies show different relaxation times for these two spins, giving clear evidence for independent spins. The unusuall y high relaxation rate of the fullerene monoanionic spins is of intrinsic o rigin and discussed in terms of a splitting of the T-1u level by a Jahn-Tel ler type distortion as proposed in the literature. We observed two distinct contributions to LESR signals, a prompt and a persistent one. Excitation l ight intensity dependence of the prompt contributions into P+ and C-60(-) E SR signals is of bimolecular type (I-0.5) and implies the mutual annihilati on within (P+...C-60(-)) pair. The persistent contribution is found to be e xcitation intensity independent and proposed to originate from deep traps d ue to disorder.