Influence of alkyl chain length in self-assembled monolayers on nanogroove-guided polymer alignment for stretchable thin-film transistors

• Alkyl of self-assembled monolayers affects molecular alignment on nanogrooved surface. • Surface energy is a key factor to increase charge carrier transport anisotropy. • A stretchable organic semiconductor film with enhanced mobility was demonstrated. The development of thin-film transistors (TFTs) based on stretchable polymer semiconductors has been extensively studied to realize stretchable electronic systems. Achieving high electrical performance in these TFTs requires precise control over stretchable polymer alignment. In this study, nanogroove-guided alignment was employed to systematically examine the effect of alkyl chain length in self-assembled monolayers (SAMs) used 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 longer SAM alkyl chain length up to octadecyl, reaching an average of 2.35 cm 2 /Vs (maximum: 2.49 cm 2 /Vs), which is 2.29 times higher than that on the flat substrate. However, the mobility decreased for the docosyl-SAM. This trend correlates with the substrate surface energy, as lower surface energy conditions enhanced dichroic ratios and mobility. The analysis of surface morphology and polarized absorption spectra of the polymer films on low-surface-energy substrates demonstrated that polymers near the gate dielectric interface were well-aligned along the nanogroove direction. This alignment is believed to play a significant role in enhancing mobility. The polymer films also exhibited excellent stretchability, maintaining a high mobility of 1.43 cm 2 /Vs even after 50 % strain.