We investigated mobility in the regioregular poly(3-octylthiophene)
(RR-P3OT) and regioregular poly(3-hexylthiophene) (RR-P3HT) by the Charge
Extraction by Linearly Increasing Voltage method (CELIV). The samples were
produced by the drop-casting and spin-coating methods on the
Indium-Tin-Oxide substrate and provided with Al contacts.
In both materials we had observed the “negative” mobility dependence at
low electric fields, i.e., the mobility used to decrease with increasing
electric field (in P3HT, this was only observed here in the drop-casted
sample). Such behaviour was never observed by CELIV in P3OT before. Data
were analysed within the Poole-Frenkel and Gaussian disorder models. The
higher energetic disorder parameters were obtained in P3OT as compared to
P3HT. This could be related to the longer side-chains of P3OT. We had
demonstrated that in both materials with increasing temperature conductivity
grows due to the thermally activated mobility.