title: Effect of Broken Conjugation on the Stretchability of Semiconducting Polymers.
abstract: Increasing the flexibility of polymer chains is a common method of increasing the deformability of solid polymeric materials. Here, the effects of "conjugation-break spacers" (CBSs)-aliphatic units that interrupt the sp2-hybridized backbone of semiconducting polymers-on the mechanical and photovoltaic properties of a diketopyrrolopyrrole-based polymer are described. Unexpectedly, the tensile moduli and cracking behavior of a series of polymers with repeat units bearing 0%, 30%, 50%, 70%, and 100% of the CBS are not directly related to the percent incorporation of the flexible unit. Rather, the mechanical properties are a strong function of the order present in the film as determined by grazing-incidence x-ray diffraction. The effect of the CBSs on the photovoltaic performance of these materials, on the other hand, is more intuitive: it decreases with increasing fraction of the flexible units. These studies highlight the importance of solid-state packing structure-as opposed to only the flexibility of the individual molecules-in determining the mechanical properties of a conjugated polymer film for stretchable, ultraflexible, and mechanically robust electronics.
authors.affiliation: Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, CA, 92093-0448, USA.
authors.forename: Suchol
authors.initials: S
authors.lastname: Savagatrup
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA.
authors.forename: Xikang
authors.initials: X
authors.lastname: Zhao
authors.affiliation: Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, CA, 92093-0448, USA.
authors.forename: Esther
authors.initials: E
authors.lastname: Chan
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN, 47907, USA. jgmei@purdue.edu.
authors.forename: Jianguo
authors.initials: J
authors.lastname: Mei
authors.affiliation: Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, CA, 92093-0448, USA. dlipomi@ucsd.edu.
authors.forename: Darren J
authors.initials: DJ
authors.lastname: Lipomi
mesh_terms: D015394:Molecular Structure; D055668:Photochemical Processes; D018583:Pliability; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*; D012666:Semiconductors
chemical_list: D011108:Polymers
keywords: bulk heterojunctions; conjugated polymers; mechanical properties; stretchable electronics; structure-property relationships