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Blinking quantum dots

Researchers in the Galli Group recently investigated the mysterious blinking process in silicon quantum dots using simulations. Their results, published in the February 28, 2015, issue of Nanoscale, bring scientists a step closer to understanding—and possibly remediating—the problem. Their work has also been featured in R&D Magazine.

Scientists have some ideas about what causes the blinking, but still don’t understand exactly how it works, said Márton Vörös, a postdoctoral researcher in the Galli group who coauthored the study.

To study blinking, the team used simulated silicon (Si) nanoparticles configured with various defects and coated with silicon dioxide. Starting with three different possible defect states, they used the Hopper supercomputer (a Cray XE6) to calculate the optical and electronic properties of the oxidized silicon nanoparticle with the scientific package called Quantum Espresso.

“Our results are the first reported ab initio calculations showing that dangling bonds on the surface of oxidized silicon nanoparticles can act as efficient non-radiative recombination centers,” said coauthor Giulia Galli, who is Liew Family professor of Electronic Structure and Simulations at the University of Chicago’s Pritzker School of Molecular Engineering. “Our findings provide an a priori validation of the interpretation of the role that dangling bond defects play in several photonic and optoelectronic devices.”

Moreover, the researchers’ techniques can be use to tackle the effects of trapping in solar cells.

“Trapping, the very same physical mechanism that causes blinking, can actually limit the efficiency of solar cells,” said Vörös.

“Now that we’ve tested this technique, we can apply it to nanocrystal solar cells, too,” Galli said.