El Labban, Abdulrahman; Warnan, Julien; Cabanetos, Clement; Ratel, Olivier; Tassone, Christopher J.; Toney, Michael F.; Beaujuge, Pierre(ACS Applied Materials & Interfaces, American Chemical Society (ACS), 2014-11-26)[Article]
(Figure Presented) 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.
Sweetnam, Sean; Graham, Kenneth; Ngongang Ndjawa, Guy Olivier; Heumüller, Thomas; Bartelt, Jonathan A.; Burke, Timothy M.; Li, Wentao; You, Wei; Amassian, Aram; McGehee, Michael D.(Journal of the American Chemical Society, American Chemical Society (ACS), 2014-10-08)[Article]
Theoretical and experimental studies suggest that energetic offsets between the charge transport energy levels in different morphological phases of polymer:fullerene bulk heterojunctions may improve charge separation and reduce recombination in polymer solar cells (PSCs). In this work, we use cyclic voltammetry, UV-vis absorption, and ultraviolet photoelectron spectroscopy to characterize hole energy levels in the polymer phases of polymer:fullerene bulk heterojunctions. We observe an energetic offset of up to 150 meV between amorphous and crystalline polymer due to bandgap widening associated primarily with changes in polymer conjugation length. We also observe an energetic offset of up to 350 meV associated with polymer:fullerene intermolecular interactions. The first effect has been widely observed, but the second effect is not always considered despite being larger in magnitude for some systems. These energy level shifts may play a major role in PSC performance and must be thoroughly characterized for a complete understanding of PSC function.
Warnan, Julien; El Labban, Abdulrahman; Cabanetos, Clement; Hoke, Eric T.; Shukla, Pradeep Kumar; Risko, Chad; Brédas, Jean Luc; McGehee, Michael D.; Beaujuge, Pierre(Chemistry of Materials, American Chemical Society (ACS), 2014-04-08)[Article]
Bartelt, Jonathan A.; Douglas, Jessica D.; Mateker, William R.; El Labban, Abdulrahman; Tassone, Christopher J.; Toney, Michael F.; Fréchet, Jean Mj J; Beaujuge, Pierre; McGehee, Michael D.(Advanced Energy Materials, Wiley, 2014-03-20)[Article]
Beiley, Zach M.; Christoforo, Mark Greyson; Gratia, Paul; Bowring, Andrea R.; Eberspacher, Petra; Margulis, George Y.; Cabanetos, Clement; Beaujuge, Pierre; Salleo, Alberto; McGehee, Michael D.(Advanced Materials, Wiley, 2013-10-07)[Article]
Cabanetos, Clement; El Labban, Abdulrahman; Bartelt, Jonathan A.; Douglas, Jessica D.; Mateker, William R.; Frechet, Jean; McGehee, Michael D.; Beaujuge, Pierre(Journal of the American Chemical Society, American Chemical Society (ACS), 2013-03-27)[Article]
Mateker, William R.; Douglas, Jessica D.; Cabanetos, Clement; Sachs-Quintana, I. T.; Bartelt, Jonathan A.; Hoke, Eric T.; El Labban, Abdulrahman; Beaujuge, Pierre; Frechet, Jean; McGehee, Michael D.(Energy and Environmental Science, Royal Society of Chemistry (RSC), 2013)[Article]
Bartelt, Jonathan A.; Beiley, Zach M.; Hoke, Eric T.; Mateker, William R.; Douglas, Jessica D.; Collins, Brian A.; Tumbleston, John R.; Graham, Kenneth; Amassian, Aram; Ade, Harald W.; Frechet, Jean; Toney, Michael F.; McGehee, Michael D.(Advanced Energy Materials, Wiley, 2012-10-26)[Article]
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