title: Enhanced solid-state order and field-effect hole mobility through control of nanoscale polymer aggregation.
abstract: Efficient charge carrier transport in organic field-effect transistors (OFETs) often requires thin films that display long-range order and close π-π packing that is oriented in-plane with the substrate. Although some polymers have achieved high field-effect mobility with such solid-state properties, there are currently few general strategies for controlling the orientation of π-stacking within polymer films. In order to probe structural effects on polymer-packing alignment, furan-containing diketopyrrolopyrrole (DPP) polymers with similar optoelectronic properties were synthesized with either linear hexadecyl or branched 2-butyloctyl side chains. Differences in polymer solubility were observed and attributed to variation in side-chain shape and polymer backbone curvature. Averaged field-effect hole mobilities of the polymers range from 0.19 to 1.82 cm(2)/V·s, where PDPP3F-C16 is the least soluble polymer and provides the highest maximum mobility of 2.25 cm(2)/V·s. Analysis of the films by AFM and GIXD reveal that less soluble polymers with linear side chains exhibit larger crystalline domains, pack considerably more closely, and align with a greater preference for in-plane π-π packing. Characterization of the polymer solutions prior to spin-coating shows a correlation between early onset nanoscale aggregation and the formation of films with highly oriented in-plane π-stacking. This effect is further observed when nonsolvent is added to PDPP3F-BO solutions to induce aggregation, which results in films with increased nanostructural order, in-plane π-π orientation, and field-effect hole mobilities. Since nearly all π-conjugated materials may be coaxed to aggregate, this strategy for enhancing solid-state properties and OFET performance has applicability to a wide variety of organic electronic materials.
authors.affiliation: Departments of Chemistry, ‡Chemical and Biomolecular Engineering, and #Physics, University of California , Berkeley, California 94720, United States.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Chen
authors.forename: Olivia P
authors.initials: OP
authors.lastname: Lee
authors.forename: Jeremy R
authors.initials: JR
authors.lastname: Niskala
authors.forename: Alan T
authors.initials: AT
authors.lastname: Yiu
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Tassone
authors.forename: Kristin
authors.initials: K
authors.lastname: Schmidt
authors.forename: Pierre M
authors.initials: PM
authors.lastname: Beaujuge
authors.forename: Seita S
authors.initials: SS
authors.lastname: Onishi
authors.forename: Michael F
authors.initials: MF
authors.lastname: Toney
authors.forename: Alex
authors.initials: A
authors.lastname: Zettl
authors.forename: Jean M J
authors.initials: JM
authors.lastname: Fréchet