А. El Labban, J. Warnan, C. Cabanetos, O. Ratel, C.J. Tassone, M.F. Toney and P.M. Beaujuge
ACS Applied Materials and Interfaces, 6(22), 19477-19481, (2014)
Side chain, Benzo[1,2-b:4,5-b]dithiophene, Thieno[3,4-c]pyrrole-4,6-dione, -conjugated polymers, Polymer crystallite, Backbone orientation
Alkyl substituents appended to the π-con-jugated 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 thepreferential orientation of the polymer crystallites in thin films (e.g.,“face-on”vs“edge-on”). Oriented crystallites, specificallycrystallites 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.