title: Dependence of crystallite formation and preferential backbone orientations on the side chain pattern in PBDTTPD polymers.
abstract: Alkyl substituents appended to the π-conjugated main chain account for the solution-processability and film-forming properties of most π-conjugated polymers for organic electronic device applications, including field-effect transistors (FETs) and bulk-heterojunction (BHJ) solar cells. Beyond film-forming properties, recent work has emphasized the determining role that side-chain substituents play on polymer self-assembly and thin-film nanostructural order, and, in turn, on device performance. However, the factors that determine polymer crystallite orientation in thin-films, implying preferential backbone orientation relative to the device substrate, are a matter of some debate, and these structural changes remain difficult to anticipate. In this report, we show how systematic changes in the side-chain pattern of poly(benzo[1,2-b:4,5-b']dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione) (PBDTTPD) polymers can (i) influence the propensity of the polymer to order in the π-stacking direction, and (ii) direct the preferential orientation of the polymer crystallites in thin films (e.g., "face-on" vs "edge-on"). Oriented crystallites, specifically crystallites that are well-ordered in the π-stacking direction, are believed to be a key contributor to improved thin-film device performance in both FETs and BHJ solar cells.
authors.affiliation: King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Saudi Arabia.
authors.forename: Abdulrahman
authors.initials: A
authors.lastname: El Labban
authors.forename: Julien
authors.initials: J
authors.lastname: Warnan
authors.forename: Clément
authors.initials: C
authors.lastname: Cabanetos
authors.forename: Olivier
authors.initials: O
authors.lastname: Ratel
authors.forename: Christopher
authors.initials: C
authors.lastname: Tassone
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: Pierre M
authors.initials: PM
authors.lastname: Beaujuge
keywords: backbone orientation; benzo[1,2-b:4,5-b′]dithiophene; polymer crystallite; side chain; thieno[3,4-c]pyrrole-4,6-dione; π-conjugated polymers