Researchers at the University of Toronto have synthesized a new class of conducting polymers — polytellurophenes — that could bring about advances in organic solar cells and thin-film transistors.

Some of the most-studied conductive polymers are the polythiophenes — long chains of sulfur-bearing rings — which are readily available as byproducts of petroleum. However, the relatively large amount of energy needed to excite electrons (known as the band gap) in these materials means that in organic solar cells, they capture only the higher-energy wavelengths of light, limiting their efficiency. Replacing sulfur with heavier elements from the same periodic table group could offer one solution.

One of the challenges was that without alkyl side chains, the tellurium-bearing ring is very unstable. “We ended up choosing an end-around method, where the alkyl chain was incorporated into the tellurophene precursor,” says Ashlee Jahnke, the PhD candidate who did the synthesis. “That way, once we closed the ring, the alkyl chain was already in place.” The method is described in a paper recently published in the Journal of the American Chemical Society.

Polytellurophenes have a band gap of about 1.4 electron volts, much lower than the 1.9 electron volts common for polythiophenes. They’re also stable at temperatures up to 300 degrees Celsius. Best of all, Jahnke’s formulations are soluble in chlorobenzene, meaning they could be spray-coated onto large sheets using technology similar to ink-jet printers. “We’re already making transistors as well as solar cells,” says Seferos. “We also hope to improve the properties by continuing to modify the structure.”