Negative mobility dependence in polythiophenes P3OT and P3HT evidenced by the charge extraction by linearly increasing voltage method ^*

¹ Department of Semiconductor Physics and Institute of Materials Science and Applied Research, Vilnius University, Saultekio 9, 10222 Vilnius, Lithuania
² DRT-LITEN-DSEN-GENEC-L2C, bât. 451, CEA Saclay, 91191 Gif-sur-Yvette, France

Corresponding author: vaidotas.kazukauskas@ff.vu.lt

Received: 25 July 2006
Revised: 13 November 2006
Accepted: 29 November 2006
Published online: 7 February 2007

Abstract

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.