One of the bugaboos hampering wearable electronics is the lack of semiconductor and wires that will work despite being stretched out of shape. Now a group of researchers thinks they may have solved the problem using a special technique wherein conductive polymer molecules are confined inside an elastomer.
The research is described in the 06 Jan 2017 issue of Science Magazine and appears in a paper that has 27 authors hailing from institutions such as Stanford University, Nanjing University in China, and Gyeongsang National University in South Korea. Their concept is based on techniques at the nanoscale. Specifically, they say the nanoconfinement of polymers can substantially improve the stretchability of polymer semiconductors, without affecting their charge transport mobility. The sort of nanoconfinement they use tends to keep cracks from forming in the conductive polymer as it stretches. They say they’ve used their technique to fabricate a semiconducting film that can be stretched up to 100% strain without affecting mobility, retaining values comparable to that of amorphous silicon.
Perhaps most interesting is that the researchers put their ideas to work in a skinlike finger-wearable driver for a light-emitting diode. The driver uses a thin-film transistor made out of a semiconducting polymer called poly(2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)diketopyrrolo[3,4-c]pyrrole-1,4-dione-alt-thieno[3,2-b]thiophen), mercifully dubbed DPPT-TT for short. The elastomer used is polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene, or SEBS. Researchers used carbon nanotube (CNT) networks as the electrodes and SEBS as the dielectric layer, stretchable substrate, and encapsulation layer. The resulting TFT conformed pretty well to a human finger and was extremely transparent, researchers say.
The method researchers used to get the right materials is called conjugated-polymer/elastomer phase separation–induced elasticity, or CONPHINE-1. The resulting materials have nanofiber networks of conducting polymers encased in SEBS. The method seems to work best for nanofiber diameters below 50 nm.
Of course, there is a long road to travel before this technique can go into wide use. Today, getting a TFT to work in any capacity using the technique is quite an achievement. Next comes getting TFTs made this way to exhibit repeatable and consistent electrical qualities and high bandwidths.
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