Highly oriented and crystalline semi-conducting and conducting polymer films prepared by high-temperature rubbing

Martin Brinkmann (1), Amer Hamidi-Sakr (1), Laure Biniek (1), Patrick Lévêque (2), Jean-Louis Bantignies (3),  David Maurin (3), Nicolas Leclerc (4)

(1) Université de Strasbourg, CNRS, ICS UPR22, F67000 Strasbourg, France
(2) Université de Strasbourg, CNRS, ENGEES, INSA, ICube UMR 7357, F-67000 Strasbourg, France
(3) Université de Montpellier, Laboratoire Charles Coulomb, F34095 Montpellier, France
(4) Université de Strasbourg, CNRS, ICPEES, UMR 7515, F67000 Strasbourg, France

This contribution focuses on recent advances in growth control and oriented crystallization of semi-conducting and conducting polymers. Particular emphasis will be given to the progress made in high-temperature rubbing of such polymers. This effective large scale alignment method can orient a large palette of polymer semiconductors (PSCs) with n- or p-type character without the use of an alignment substrate. The concurrent roles of the polymer molecular weight distribution and the rubbing temperature (TR) on the in-plane orientation have been rationalized for P3HT and PBTTT. Correlations are drawn between nanomorphology/crystallinity on one side and charge transport and optical properties on the other side.a It is shown that the exciton bandwidth in P3HT crystals is determined by the length of the average planarized chain segments in the crystals. The high alignment and crystallinity observed for TR > 200 °C cannot translate to high hole mobilities parallel to the rubbing because of the adverse effect of amorphous interlamellar zones interrupting charge transport between crystalline lamellae. In a second part of this presentation, we show that soft doping of aligned PSCs yields highly oriented conducting polymer films with anisotropic charge conductivity and thermoelectric properties that are enhanced along the rubbing direction.b The unique in-plane orientation in such conducting polymer films helps rationalizing the mechanism of redox doping.

(a) A. Hamidi-Sakr et al., Adv. Funct. Mat. 2016, 26, 408 (link)
(b) A. Hamidi-Sakr, et al, Adv. Funct. Mat. 2017, 1700173 (link)