February 25, 2016

New Discovery at UMass Amherst May Lead to More Efficient Solar and Opto-Electronic Devices


Fluorescence image of self-assembled TAT crystalline nanowires. Inset shows
a structural schematic of the TAT crystal packing geometry and direction of charge separation.
A new property discovered in the organic semiconductor molecule could lead to more efficient
and cost-effective materials for use in cell phone and laptop displays, among other applications. Courtesy UMass Amherst/Mike Barnes

(February 25, 2016)  Chemists and polymer scientists collaborating at the University of Massachusetts Amherst report in Nature Communications this week that they have for the first time identified an unexpected property in an organic semiconductor molecule that could lead to more efficient and cost-effective materials for use in cell phone and laptop displays, for example, and in opto-electronic devices such as lasers, light-emitting diodes and fiber optic communications.

Physical chemist Michael Barnes and polymer scientist Alejandro Briseño, with doctoral students Sarah Marques, Hilary Thompson, Nicholas Colella and postdoctoral researcher Joelle Labastide, discovered the property, directional intrinsic charge separation, in crystalline nanowires of an organic semiconductor known as 7,8,15,16-tetraazaterrylene (TAT).

The researchers saw not only efficient separation of charges in TAT, but a very specific directionality that Barnes says “is quite useful. It adds control, so we’re not at the mercy of random movement, which is inefficient. Our paper describes an aspect of the nanoscopic physics within individual crystals, a structure that will make it easier to use this molecule for new applications such as in devices that use polarized light input for optical switching. We and others will immediately exploit this directionality.”

He adds, “Observing the intrinsic charge separation doesn’t happen in polymers, so far as we know it only happens in this family of small organic molecule crystalline assemblies or nanowires. In terms of application we are now exploring ways to arrange the crystals in a uniform pattern and from there we can turn things on or off depending on optical polarization, for example.”

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