The Effects of Long Range Sidechain Ordering on Backbone Ordering and Optoelectronic Properties in Semiconducting Polymers

Published

December 12, 2018

Author(s)

Joshua H. Carpenter, Masoud Ghasemi, Eliot Gann, Indunil Angunawela, Samuel Stuard, Liang Yan, Earl RItchie, Brendan O'Connor, Dean DeLongchamp, Harald Ade

Abstract

Molecular ordering and packing greatly impacts the electronic and optoelectronic properties of semiconducting polymers. Despite much prior effort, the competing or synergistic ordering of the sidechains and aromatic cores has never been fully researched. We report here the discovery in six representative high performance semiconducting polymers of a highly ordered sidechain phase, obtained by drop-casting from relatively high boiling point solvents at room temperature, as determined from distinct spectroscopic and scattering signatures that resembles neat alkane crystals. The sidechain ordering has an unusually large coherence length (≥ 150 intermolecular spacings), induces torsional/twisting backbone disorder, and results in a vertically layered nanostructure, with 2D ordered sidechain layers alternating with disordered backbone layers. Calorimetry and in- situ variable temperature scattering measurements in PBnDT-FTAZ clearly delineate this competition of incompatible ordering that prevents the simultaneous long range order of both moieties and possibly lowers the overall ordering under any conditions. We exploited this sidechain ordering to fabricate PBnDT-FTAZ films with an edge-on texture, though PBnDT-FTAZ typically adopts a face-on texture. OFETs employing these edge-on films have in-plane charge carrier mobilities 2.5 times that of face-on control devices, demonstrating that this highly ordered sidechain phase could be utilized to improve microstructure for semiconducting polymer applications. However, DSC and the slow solvent quench imply that the state with the highly ordered sidechain phase is the thermodynamically stable state and thus as-cast, quenched, π-stacked materials are unstable at RT as confirmed by optical microscopy. The observed competition between backbone and sidechain ordering implies that rational molecular design could produce synergistic rather than destructive ordering for both moieties. Given the large sidechain coherence lengths repor

Citation

Advanced Functional Materials

Pub Type

Journals

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Keywords

polymer sidechains, polymer ordering, NEXAFS, GIWAXS

Citation

Carpenter, J. , Ghasemi, M. , Gann, E. , Angunawela, I. , Stuard, S. , Yan, L. , RItchie, E. , O'Connor, B. , DeLongchamp, D. and Ade, H. (2018), The Effects of Long Range Sidechain Ordering on Backbone Ordering and Optoelectronic Properties in Semiconducting Polymers, Advanced Functional Materials, [online], https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=926308 (Accessed April 25, 2024)