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

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 cm²/V s at 1 ps to 10^-6 cm²/V s within 1 μs. 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.