Samsung Advanced Institute of Technology

The development of thin-film transistors (TFTs) utilizing stretchable polymer semiconductors has been extensively investigated to realize stretchable electronic systems. Achieving high electrical performance in these TFTs requires precise control of the alignment of stretchable polymers. In this study, nanogroove-guided alignment was employed to systematically investigate the influence of alkyl chain length in self-assembled monolayers (SAMs) for substrate modification on the molecular alignment and TFT characteristics of stretchable polymer films, comprising a diketopyrrolopyrrole-based polymer and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene-elastomer. The evaluation of TFT characteristics revealed that the mobility increased with the SAM alkyl chain length up to octadecyl, achieving an average maximum of 2.35 cm²/V·s (individual maximum: 2.49 cm²/Vs), but decreased for docosyl. This trend correlates with the surface energy on the substrate, as low surface energy conditions enhanced dichroic ratios and mobility. Phase images and polarized ultraviolet-visible-near infrared absorption spectra of the polymer films on low-surface-energy substrates revealed that polymers near the gate dielectric interface were well-aligned along the nanogroove direction. This alignment is considered to significantly contribute to the enhanced charge carrier mobility. The polymer films demonstrated excellent stretchability, retaining a high mobility of 1.43 cm²/V·s after 50% strain, with only a slight decrease from the unstretched state.