Mobility and density relaxation of photogenerated charge carriers in organic materials

We have measured mobility and density relaxation of photogenerated charge carriers in regiorandom poly(3-hexylthiophene) using novel extraction current transient techniques. We show how to obtain time-dependent mobility μ and charge carrier density p using independent measurements. The results show μ∝t ^-0.42 independent on charge carrier density. The carrier density follows a bimolecular decay with the bimolecular recombination coefficient β=7.2×10^-13 cm³/s. The measured time-of-flight current follows closely the estimated time decay as j(t)∝p(t)μ(t), with deviation arising from extraction of the generated charge carriers.