Ultrafast Dynamics of Carrier Mobility in a Conjugated Polymer Probed at Molecular and Microscopic Length Scales

Abstract

We used time-resolved electric-field-induced second-harmonic generation to probe the charge-carrier-mobility dynamics in amorphous organic materials on an ultrafast time scale. We were able to show that the mobility in poly-spiro-bifluorene-co-benzothiadiazol decreases from $0.1\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{s}$ at 1 ps to ${10}^{\ensuremath{-}6}\text{ }\text{ }{\mathrm{cm}}^{2}/\mathrm{V}\text{ }\mathrm{s}$ within $1\text{ }\ensuremath{\mu}\mathrm{s}$. We attribute this dramatic decrease to the relaxation of the charge carriers within the density of states, clearly demonstrating the impact of disorder on the nanoscale charge transport in amorphous semiconductors.