Ultrafast charge carrier mobility dynamics in poly(spirobifluorene-co-benzothiadiazole): Influence of temperature on initial transport

In this work we examine the influence of temperature on the transport dynamics of photogenerated charge carriers in pi-conjugated poly(spirobifluorene-co-benzothiadiazol) films. Investigations were performed by picosecond time-resolved electric field induced second-harmonic technique. The mobility is independent of temperature during the initial 100 ps. During this time, the carriers drift about 6 nm under an applied field of 1.2 x 10(6) V/cm, and the mobility decreases from 3 x 10(-2) cm(2)/V s by one order of magnitude. We attribute this change in mobility to the intrachain charge transport during carrier relaxation down in the density of states. At a time delay of 1 ns the transport is temperature dependent with an activation energy of about 22 meV.