A superstretchy transistor

Today’s electronic devices are rigid and brittle creations, largely because those are the traits of the semiconducting materials they depend on. But a clutch of materials scientists and engineers have been working to design a new generation of stretchable electronics that could serve as wearable devices, implantable biosensors, or electronic skins. Now Zhenan Bao and her colleagues at Stanford University have reported a leap forward in that pursuit: They’ve built a wearable transistor that’s as supple and durable as human skin. It works whether it’s twisted like a candy wrapper, stretched to twice its length, or poked by a nail. At the heart of the design is a semiconducting polymer known as diketopyrrolopyrrole-thienothiophene, or DPPT-TT. The polymer’s high charge-carrier mobility had been largely attributed to its crystalline structure, which facilitates the hopping of electrons between molecules. But crystallinity also renders the polymer stiff. Bao and her colleagues were able to impart flexibility—while preserving electronic performance—by exploiting effects of nanoconfinement. The trick was to prepare the polymer in an elastomer matrix. If the two materials are combined in just the right proportions, the long-chain DPPT-TT molecules spontaneously aggregate into nanofibers, as illustrated in the image. Unable to fold and assemble into crystals, the molecules remain elongated and flexible. And because the semiconducting molecules are tightly bundled, electrons can easily hop between them, as they would in a crystal. Importantly, the technique isn’t limited to DPPT-TT. Bao and company used the method to build similarly stretchable transistors from four other semiconducting polymers. (J. Xu et al., Science 355, 59, 2017 .)