Stretchable and Conductive Li-Complexed Poly(3-hexylthiophene) Nanofibrils/Elastomer Composites for Printed Electronic Skins

Semiconducting polymers are considered essential materials because of the dramatically increasing demand for deformable electronic and energy devices. However, an improvement in both the electrical conductivity and mechanical stretchability of these polymers has been challenging. In this study, we designed a composite material comprising Li-complexed poly(3-hexylthiophene) nanofibrils (Li-P3HT) and poly(styrene-b-butadiene-b-styrene) (SBS) as the conductive and stretchable active layers of electronic skins (e-skins). The cooling process of a P3HT/SBS solution leads to the one-dimensional growth of P3HT crystals due to strong π–π interactions between the thiophene backbones, which assists in the formation of percolation networks within the SBS matrix after spin coating. The complexation of Li+ and thiophene backbones significantly increased the hole concentration of the nanocomposites. The resulting conductivity was found to be 1.27 × 10–3 S cm–1, which is 5.7 times higher than that of pristine P3HT/SBS. Furthermore, the stretchable SBS matrix led to an excellent retention of long electrical pathways via percolated Li-P3HT nanofibrils for a strain of up to 50%. The printed Li-P3HT/SBS arrays on Ag nanowire/Ecoflex stretchable electrodes were utilized as the active layers of high-performance strain and pulse sensors.