Molecularly stretchable electronics

This Perspective describes electronic materials whose molecular structure permits extreme deformation without the loss of electronic function. This approach-molecularly stretchable" electronics is complementary to the highly successful approaches enabled by stretchable composite materials. We begin by identifying three general types of stretchable electronic materials: (1) random composites of rigid structures sitting atop or dispersed in an elastic matrix, (2) deterministic composites of patterned serpentine, wavy, or fractal structures on stretchable substrates, and (3) molecular materials-noncomposite conductors and semiconductors-that accommodate strain intrinsically by the rational design of their chemical structures. We then identify a short-term and a long-term goal of intrinsically stretchable organic electronics: the short-term goal is improving the mechanical stability of devices for which commercialization seems inevitable; the long-term goal is enabling of electronic devices in which every component is highly elastic, tough, ductile, or some combination thereof. Finally, we describe our and others' attempts to identify the molecular and microstructural determinants of the mechanical properties of organic semiconductors, along with applications of especially deformable materials in stretchable and mechanically robust devices. Our principal conclusion is that while the field of plastic electronics has achieved impressive gains in the last several years in terms of electronic performance, all semiconducting polymers are not equally "plastic" in the sense of "deformable", and thus materials tested on glass substrates may fail in the real world and may not be amenable to stretchable-or even modestly flexible-systems. The goal of this Perspective is to draw attention to the ways in which organic conductors and semiconductors specifically designed to accommodate large strains can enable highly deformable devices, which embody the original vision of organic electronics.