Dynamics of charge carriers photoinduced in poly(3-dodecylthiophene)/fullerene composite

Radical pairs, polarons and fullerene anion-radicals, photoinduced by laser with photon energies of 1.88, 2.22 and 2.75 eV in the poly(3-dodecylthiophene)/[6,6]-phenyl-C61-butanoic acid methyl ester (P3DDT/PCBM) bulk heterojunction, were studied over a wide temperature range. The number of these centers was found to decrease with the increase in laser photon energy. Both the spin–lattice and spin–spin relaxation times of fullerene anion-radicals and the spin–spin relaxation time of polarons change monotonically with temperature, whereas the interaction of polarons with the lattice is characterized by extreme temperature dependence. The one-dimensional polaron diffusion along the polymer chain and the rotation of fullerene near it own main axis was shown to follow the activation Elliot hopping model and to be governed by the photon energy. The deviation in activation energies for polaron and anion-radical motion and the difference in their dependence on the laser photon energy prove the non-interacting character of these charge carriers photoinduced in the P3DDT/PCBM bulk heterojunction.