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. The kinetics of the structural modification upon doping was further analyzed by in situ grazing incidence X-ray diffraction. Dopant molecules intercallate in the layers of alkyl side chains of the polymer and tend to orient with their long axis perpendicular to the polymer backbone. The kinetics of doping is a function of the structure of the alkyl side chains (interdigitated versus non interdigitated).
(a) A. Hamidi Sakr et al., Adv. Funct. Mat. 2016, 26, 408.
(b) A. Hamidi-Sakr, et al, Adv. Funct. Mat. 2017, 1700173