Stretchable Redox-active Semiconducting Polymers for High-performance Organic Electrochemical Transistors

Organic electrochemical transistor (OECT) is an emerging device platform for next-generation bioelectronics owing to its uniquely high amplification and sensitivity to biological signals. For achieving seamless tissue-electronics interfaces for accurate signal acquisition, skin-like softness and stretchability are essential requirements, which have not yet been imparted onto high-performance OECTs, largely due to the lack of stretchable redox-active semiconducting polymers. Here, we report a stretchable semiconductor for OECT devices, namely poly(2-(3,3'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-[2,2'-bithiophen]-5)yl thiophene) (p(g2T-T)), which gives exceptional stretchability over 200% strain and 5000 repeated stretching cycles, together with the OECT performance on par with the state of the art. Validated by the systematic characterizations and the comparisons of different polymers, the key design features of this polymer that enable the combination of high stretchability and high OECT performance are non-linear backbone architecture, moderate side-chain density, and sufficiently high molecular weight. Using this highly stretchable polymer semiconductor, we fabricated an intrinsically stretchable OECT with the high normalized transconductance (∼223 S cm-1 ) and biaxial stretchability up to 100% strain. Furthermore, we demonstrate on-skin electrocardiogram (ECG) recording that combines built-in amplification and unprecedented skin conformability.