Wearable electronics: Stretching the limits

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Wearable electronic devices are designed to maintain their functionality throughout multiple bending cycles. Because they require structural flexibility, such devices have to be fabricated from plastic-like materials that are far less rigid than conventional high-mobility semiconductors. However, in softer semiconductors such as π-conjugated polymers achieving the desired level of stretchability in combination with good charge transport properties remains elusive. High-mobility polymers with rigid chains and improved crystallinity tend to be brittle, while their amorphous and mechanically flexible counterparts have low electrical conductivity. Jie Xu, Sihong Wang et al. have now shown how this mutual exclusivity of mechanical and electrical performance can potentially be overcome via nanoconfinement.

Constraining polymer chains into nanosized dimensions is known to modify their kinetic and thermodynamic properties. If successfully executed, this approach may result in the improved ductility and suppressed crystallinity of the confined polymer. The so-called CONPHINE methodology inspired by the idea of nanoconfinement was applied to fabricate a hybrid material made of conducting DPPT-TT nanofibrils embedded into SEBS, a highly deformable elastomer. Increased chain dynamics and reduced crystallization were observed in the thinnest polymer/SEBS films. The aggregates of the conducting polymer remain perfectly interconnected and good charge transport is maintained throughout the nanoscale network. The picture shows a flexible transistor fabricated from the DPPT-TT/SEBS stretched to twice its length. Only minimal loss in mobility and on current is observed in this experiment. During the strain test conducted on a SEBS substrate, conducting channels showed no visible cracking even when investigated at the nanoscale. The stretchable thin film transistors were able to sustain their performance after more than 1,000 repeated stretching cycles. The method was proven equally successful when tested on other conducting polymers, with one of them exhibiting mobility of 1 cm2 Vs−1 at 100% strain.



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