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April 15th, 2009

Better photocells from bigger Buckyballs

Abstract:
Much research activity is presently devoted to organic photovoltaic devices (OPV), in particular ones comprising polymers as donors and a variety of C60 fullerenes with organic molecules attached as acceptors. Now, a group of scientists collaborating from several research institutions, namely the Georgetown University, Washington DC, Luna Innovations Inc., Virginia, the Friedrich-Alexander-Universität, Erlangen, Germany, the National Renewable Energy Laboratory, Colorado, and the University of Santa Barbara have developed a novel fullerene species for this application [Ross, et al., Nature Materials (2009), doi:10.1038/NMAT2379].

"We believe that our discovery is a significant contribution to the improvement in conversion efficiencies of organic solar cells," says Martin Drees, corresponding author. In contrast to the acceptor materials utilized to date, Drees and his colleagues used fullerenes large enough to incarcerate trimetallic nitrides (therefore called trimetallic nitride endohedral fullerenes, or TNEFs) and filled them with Lu3N. The main advantage over the presently used empty C60 molecules and their derivatives is the higher open circuit voltage. Drees and his group found values of about 890 mV (in comparison to 630 mV for present state-of-the-art C60 devices), in fact the highest reported for any fullerene OPV. The reason for the low voltage output of the C60 devices is the orbital mismatch of the donor polymer and the fullerene acceptors, a situation which the researchers could significantly improve by incorporating Lu3N-ions in the bigger fullerenes.

Source:
materialstoday.com

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