title: In situ probing of the crystallization kinetics of rr-P3HT on single layer graphene as a function of temperature.
abstract: We studied the molecular packing and crystallization of a highly regio-regular semiconducting polymer poly(3-hexylthiophene) (P3HT) on both single layer graphene and silicon as a function of temperature, during cooling from the melt. The onset of crystallization, crystallites' size, orientation, and kinetics of formation were measured in situ by synchrotron grazing incidence X-ray diffraction (GIXD) during cooling and revealed a very different crystallization process on each surface. A favored crystalline orientation with out of plane π-π stacking formed at a temperature of 200 °C on graphene, whereas the first crystallites formed with an edge-on orientation at 185 °C on silicon. The crystallization of face-on lamellae revealed two surprising effects during cooling: (a) a constant low value of the π-π spacing below 60 °C; and (b) a reduction by half in the coherence length of face-on lamellae from 100 to 30 °C, which corresponded with the weakening of the 2nd or 3rd order of the in-plane (k00) diffraction peak. The final ratio of face-on to edge-on orientations was 40% on graphene, and 2% on silicon, revealing the very different crystallization mechanisms. These results provide a better understanding of how surfaces with different chemistries and intermolecular interactions with the polythiophene polymer chains lead to different crystallization processes and crystallites orientations for specific electronic applications.
authors.affiliation: Nano-Engineered Materials and Organic Electronics Laboratory, Umeå Universitet, Umeå 90187, Sweden. david.barbero@umu.se.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Boulanger
authors.affiliation: Department of Physics, McGill University, Montréal, Québec H3A 2T8, Canada.
authors.forename: Victor
authors.initials: V
authors.lastname: Yu
authors.affiliation: Department of Physics, McGill University, Montréal, Québec H3A 2T8, Canada.
authors.forename: Michael
authors.initials: M
authors.lastname: Hilke
authors.affiliation: Stanford Synchrotron Radiation Lightsource, Menlo Park, CA, USA.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.affiliation: Nano-Engineered Materials and Organic Electronics Laboratory, Umeå Universitet, Umeå 90187, Sweden. david.barbero@umu.se.
authors.forename: David R
authors.identifier: http://orcid.org/0000-0002-5507-933X
authors.initials: DR
authors.lastname: Barbero