Organic semiconductors (OSCs) have properties that allow them to fill application spaces beyond silicon, specifically those of flexible, wearable, implantable, and biodegradable electronics. More widespread deployment of these technologies is dependent on industrially viable fabrication processes, such as roll-to-roll printing. Solution shearing is a deposition technique that not only can be easily adapted to such processes, but also has been demonstrated to produce highly aligned and high crystalline small molecule OSC thin films. In-plane alignment of OSCs in the active layers of electronic devices can impart desirable properties, such as reduced device cross-talk due to charge transport anisotropy, polarized light absorption or emission, and enhanced charge transport performance because of better ordering.<br/>We have observed the alignment of a diketopyrrolopyrrole-terthiophene donor-acceptor polymer deposited directly from solution without surface templating or complex pre- or postdeposition processing; a dichroic ratio up to ~7 was achieved. The degree of alignment in the thin films were tuned by controlling the coating speed and was found to be a competition between the shear alignment of polymer chains in solution and stochastic nucleation. Unlike previous reports however, no charge transport anisotropy was observed. Coupled with the observed anisotropy in X-ray diffraction data and the relative degrees of crystallinity in these films, these results are consistent with polymer alignment in both the amorphous and crystalline regions of the films. Alignment is directly influenced by deposition parameters like temperature and substrate treatment or chemical parameters like alkyl side-chain length. Furthermore, solvent choice had a complex effect on film deposition, sometimes yielding no alignment. Our work shows that solution shearing can be used to tune in-plane polymer alignment in a single-step process without substrate patterning or postdeposition treatments.

Direct, single-step alignment of semiconducting polymer thin films and factors influencing their deposition via solution shearing

253rd National Meeting (2017)

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