Stretchable Polymer Semiconductors for Plastic Electronics

Conjugated polymers have evolved significantly in the past decade and have proven to be more than poorly conducting plastics. Instead, improved understanding has resulted in respectable charge-carrier mobilities and power-conversion efficiencies achieved by various donor-acceptor-type semiconducting polymers. However, their advantages in mechanical flexibility and deformability seem to have conflicting molecular design requirements from those for high charge-carrier transporting properties. It is therefore a challenge to enhance the mechanical compliance of semiconducting polymers suitable for stretchable device applications. This progress report starts with a brief introduction to fracture mechanics and mechanical characterization techniques for thin polymer films, in order to consider the limitations and rationalization of current definition and parameters for stretchability. It then surveys different strategies that can be applied to improve the mechanical robustness and stretchability of polymer semiconductors, in particular focusing on molecular design aspects such as molecular weight and regioregularity, structural modifications in the polymer backbone and side chain, and postpolymerization modifications including blending and cross-linking. Finally, directions for future development of next-generation stretchable conjugated polymers are indicated.