Environmentally Stable and Stretchable Polymer Electronics Enabled by Surface-Tethered Nanostructured Molecular-Level Protection

Soft and stretchable bioelectronics made of polymeric materials are envisioned to be promising platforms for next-generation wearable and implantable applications, enabling real-time health monitoring, timely medical diagnosis/treatments, smart prosthetics, and brain-machine interfaces. However, the environmental instability of polymer semiconductors (PSCs) remains to be a long-standing concern that hinders their practical deployment. Previous reports of addressing the challenge are mainly focused on encapsulation of the entire electronic device with stretchable polymer coatings, which usually have high water permeability and thus exhibit poor protection effect due to large free volume. In this work, we developed a simple and effective molecular protecting method to improve PSC operational stability in organic field-effect transistors, which involved covalent functionalization of fluoroalkyl-chains onto stretchable PSC film surface to form densely packed nanostructures. The fluorinated molecular protection layer (FMPL) with nanometer thickness exhibited orders of magnitude lower water permeability than that of various stretchable elastomers and dense plastics, and even on par with some inorganics. More importantly, the FMPL maintained its protecting function under mechanical deformation. Utilizing multiple nanoscale characterization tools, we quantitatively elucidated that the FMPL’s remarkable ability to block water absorption and diffusion was attributed to its hydrophobicity and high surface fluorination density. The FMPL’s protection effect outperformed various thick stretchable polymer encapsulants, leading to a stable PSC mobility of ~1 cm² V^-1 s^-1 in harsh environments such as in 85-90 % humidity air for 56 days and water or artificial sweat for 42 days. This strategy can be potentially implemented into a wide range of devices such as sensors, organic light-emitting diodes, solar cells, and batteries, building highly integrated stretchable electronics with prolonged operation lifetime.