Details

Autor(en) / Beteiligte

• Persson, Nils E
• Engmann, Sebastian
• Richter, Lee J
• DeLongchamp, Dean M

Titel

In Situ Observation of Alignment Templating by Seed Crystals in Highly Anisotropic Polymer Transistors

Ist Teil von

• Chemistry of materials, 2019-06, Vol.31 (11), p.4133-4147

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2019

Link zum Volltext

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Due to the highly directional nature of transport in polymer-based organic field-effect transistors (OFETs), alignment of the polymer backbone can significantly affect device performance. While many methods of alignment have been detailed, the mechanism of alignment is rarely revealedespecially in cases of flow-induced alignment. Polymer aggregates are often observed in highly aligned systems, but their role is similarly unclear. Here, we present a comprehensive characterization of blade-coated P­(NDI2OD-T2) (N2200) for OFET applications, including a rigorous, multimodal characterization of its in-plane alignment. Film thickness follows the expected power-law dependence on coating speed, while bulk polymer backbone orientation transitions from perpendicular to parallel to the coating direction as speed is increased. Charge carrier mobility >2 cm2/(V s) is achieved parallel to the coating direction for aligned N2200 coated at 5 mm/s and is found to be strongly correlated with the in-plane alignment of the fibrillar morphology at the film’s surface, characterized with atomic force microscopy and near-edge X-ray absorption. We develop a model of N2200 crystal anisotropy through rotational scans of grazing incidence wide-angle X-ray scattering (GIWAXS) and use it to analyze simultaneous in situ GIWAXS and UV–vis reflectance data from polymer solutions coated at 5 mm/s. A small population of crystals align early in the drying process, but bulk alignment occurs very late in the drying process, likely mediated by a lyotropic liquid crystal phase transition templated by the aligned crystals. Our characterization also suggests that the majority of material in N2200 thin films is noncrystalline at these conditions.