title: Microfluidic Crystal Engineering of π-Conjugated Polymers.
abstract: Very few studies have reported oriented crystallization of conjugated polymers directly in solution. Here, solution crystallization of conjugated polymers in a microfluidic system is found to produce tightly π-stacked fibers with commensurate improved charge transport characteristics. For poly(3-hexylthiophene) (P3HT) films, processing under flow caused exciton bandwidth to decrease from 140 to 25 meV, π-π stacking distance to decrease from 3.93 to 3.72 Å and hole mobility to increase from an average of 0.013 to 0.16 cm(2) V(-1) s(-1), vs films spin-coated from pristine, untreated solutions. Variation of the flow rate affected thin-film structure and properties, with an intermediate flow rate of 0.25 m s(-1) yielding the optimal π-π stacking distance and mobility. The flow process included sequential cooling followed by low-dose ultraviolet irradiation that promoted growth of conjugated polymer fibers. Image analysis coupled with mechanistic interpretation supports the supposition that "tie chains" provide for charge transport pathways between nanoaggregated structures. The "microfluidic flow enhanced semiconducting polymer crystal engineering" was also successfully applied to a representative electron transport polymer and a nonhalogenated solvent. The process can be applied as a general strategy and is expected to facilitate the fabrication of high-performance electrically active polymer devices.
authors.affiliation: State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University , Shanghai 201620, People's Republic of China.
authors.forename: Gang
authors.initials: G
authors.lastname: Wang
authors.forename: Nils
authors.initials: N
authors.lastname: Persson
authors.forename: Ping-Hsun
authors.initials: PH
authors.lastname: Chu
authors.forename: Nabil
authors.initials: N
authors.lastname: Kleinhenz
authors.forename: Boyi
authors.initials: B
authors.lastname: Fu
authors.forename: Mincheol
authors.initials: M
authors.lastname: Chang
authors.forename: Nabankur
authors.initials: N
authors.lastname: Deb
authors.affiliation: NIST Center for Neutron Research, National Institute of Standards and Technology , Gaithersburg, Maryland 20899, United States.
authors.forename: Yimin
authors.initials: Y
authors.lastname: Mao
authors.affiliation: State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Material Science and Engineering, Donghua University , Shanghai 201620, People's Republic of China.
authors.forename: Hongzhi
authors.initials: H
authors.lastname: Wang
authors.forename: Martha A
authors.initials: MA
authors.lastname: Grover
authors.forename: Elsa
authors.initials: E
authors.lastname: Reichmanis
keywords: charge transport mobility; conjugated polymer; crystal engineering; microfluidic; tie-chains