Exploiting pi-pi Stacking for Stretchable Semiconducting Polymers

Abstract

Although intermolecular charge transport is known to occur via pi-pi stacking, the influence of pi-pi stacking on the mechanical properties of polymers has received little attention compared with other dynamic noncovalent interactions. Herein, we demonstrate a method to enhance stretchability via lowering crystallinity and increasing pi-pi stacking of thiophene-based random copolymer chains, which causes pi-pi stacking-induced polymer networks to form within the fully conjugated semiconducting polymer matrix. The polymer networks contain coiled amorphous chains that aid energy dissipation when the polymer film is subjected to strain; furthermore, the pi-pi stacking prevents the chains from irreversible sliding out of place due to the applied strain and provides interchain charge transport. Consequently, we are able to improve the polymer's mechanical properties such as elongation at break, tensile strength, and toughness along with charge mobility. Additionally, our polymer shows great tolerance to a 40% strain without a decrease in mobility while maintaining a stable electrical performance even after 5000 stretching cycles at 30% strain.