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DoE's Brookhaven Lab Tests Hybrid Nanoparticles for Energy Sources

by Editor1 last modified May 24, 2011 - 20:21

Scientists at the U.S. Department of Energy’s Brookhaven National Laboratory have assembled nanoscale pairings of quantum dots and fullerenes that show promise as miniaturized power sources. The two-nanoparticle systems can convert light to electricity in a precisely controlled way.

DoE's Brookhaven Lab Tests Hybrid Nanoparticles for Energy Sources

Mircea Cotlet and Zhihua Xu of DoE’s Brookhaven National Lab investigate quantum dot-fullerene pairings.

The team from Brookhaven’s Center for Functional Nanomaterials (CFN) developed a precision fabrication method which allows them to carefully control particle size and inter-particle distance.

This added control, in turn, lets researchers work with light-induced electron transfer at the molecular level – even between individual quantum dots and fullerenes. As a result, these researchers may be tapping into methods to use improve fabrication techniques for solar panels, among other uses.

“This is the first demonstration of a hybrid inorganic/organic, dimeric (two-particle) material that acts as an electron donor-bridge-acceptor system for converting light to electrical current,” said Brookhaven CFN physical chemist Mircea Cotlet.

By varying the length of the ‘linker’ molecules, as well the size of the quantum dots, researchers found they could control the rate and the magnitude of fluctuations in light-induced electron transfer. The team found that reducing quantum dot size and the length of the linker molecules led to enhancements in the electron transfer rate and suppression of electron transfer fluctuations.

“This control makes these dimers promising power-generating units for molecular electronics or more efficient photovoltaic solar cells,” Cotlet said. The suppression of electron transfer fluctuation in dimers with smaller quantum dot size leads to a stable charge generation rate, also promising for the use of dimers in molecular electronics, he added.

The complete assembly process takes place on a surface and in a stepwise fashion to limit the interactions of the components (particles), which could otherwise combine in a number of ways if assembled by solution-based methods. This surface-based assembly also achieves controlled, one-to-one nanoparticle pairing.

“This method removes ensemble averaging and reveals a system’s heterogeneity — for example fluctuating electron transfer rates — which is something that conventional spectroscopic methods cannot always do,” Cotlet said.

Quantum dots have been combined with electron-accepting materials (dyes, fullerenes, titanium oxide, etc.) to produce dye-sensitized and hybrid solar cells. The hope is that quantum dots’ light-absorbing and size-dependent emission properties could boost power conversion rates of such devices. To date, however, such rates remain low.

Nanoscientists working on molecular electronics are interested in these types of organic donor-bridge-acceptor systems for two key reasons: (1) They have a wide range of charge transport mechanisms; and (2) They offer charge-transfer properties can be controlled by varying their chemistry.

This work, which appears in Angewandte Chemie, was funded by the DOE Office of Science. Zhihua Xu, a CFN with materials scientist at Brookhaven also contributed to the research.

A U.S. patent application is pending on the method and the materials resulting from using the technique, and the technology is available for licensing from U.S. DoE, by contacting Kimberley Elcess at (631) 344-4151 for more information.