Tailoring the Morphology of a Diketopyrrolopyrrole-based Polymer as Films or Wires for High-Performance OFETs using Solution Shearing

Conjugated polymers often show efficient charge carrier transport along their backbone which is a primary factor in the electrical behavior of Organic Field Effect Transistor (OFETs) devices fabricated from these materials. Herein, a solution shearing procedure is reported to fabricate micro/nano wires from a diketopyrrolopyrrole (DPP)-based polymer. Millimeter to nanometer long polymer wires orientated in the coating direction are developed after a thorough analysis of the deposition conditions. It shows several morphological regimes-film, transition, and wires and experimentally derive a phase diagram for the parameters coating speed and surface energy of the substrate. The as-fabricated wires are isolated, which is confirmed by optical, atomic force, and scanning electron microscopy. Beside the macroscopic alignment of wires, cross-polarized optical microscopy images show strong birefringence suggesting a high degree of molecular orientation. This is further substantiated by polarized UV-Vis-NIR spectroscopy, selected area electron diffraction transmission electron microscopy, and grazing-incidence wide-angle X-ray scattering. Finally, an enhanced electrical performance of single wire OFETs is observed with a 15-fold increase in effective charge carrier mobility to 1.57 cm2 V-1 s-1 over devices using films (0.1 cm2 V-1 s-1) with similar values for on/off current ratio and threshold voltage. In this article, a solution shear coating procedure for fabricating micro/nano wires from a diketopyrrolopyrrole-based (DPP) polymer has been developed. The detailed analyses (POM, AFM, SEM, UV-Vis-NIR, GIWAXS, SAED TEM) revealed distinct regimes-film, transition, and wires-presented as a phase diagram. Moreover, single-wire OFETs showed a 15-fold increase in effective charge carrier mobility (1.57 cm2 V-1 s-1) compared to films (0.1 cm2 V-1 s-1).image