am505280a_si_001.pdf (9.02 MB)
Dependence of Crystallite Formation and Preferential Backbone Orientations on the Side Chain Pattern in PBDTTPD Polymers
journal contribution
posted on 2014-11-26, 00:00 authored by Abdulrahman El Labban, Julien Warnan, Clément Cabanetos, Olivier Ratel, Christopher Tassone, Michael
F. Toney, Pierre M. BeaujugeAlkyl
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.