Research highlights potential for improved s...( LOS ALAMOS New Mexico February 10 20...)

LOS ALAMOS, New Mexico, February 10, 2009A team of Los Alamos researchers led by Victor Klimov has shown that carrier multiplicationwhen a photon creates multiple electronsis a real phenomenon in tiny semiconductor crystals and not a false observation born of extraneous effects that mimic carrier multiplication. The research, explained in a recent issue of Accounts of Chemical Research, shows the possibility of solar cells that create more than one unit of energy per photon.

Questions about the ability to increase the energy output of solar cells have prompted Los Alamos National Laboratory researchers to reassess carrier multiplication in extremely small semiconductor particles.

When a conventional solar cell absorbs a photon of light, it frees an electron to generate an electrical current. Energy in excess of the amount needed to promote an electron into a conducting state is lost as heat to atomic vibrations (phonons) in the material lattice. Through carrier multiplication, excess energy can be transferred to another electron instead of the material lattice, freeing it to generate electrical currentthereby yielding a more efficient solar cell.

Klimov and colleagues have shown that nanocrystals of certain semiconductor materials can generate more than one electron after absorbing a photon. This is partly due to strengthened interactions between electrons squeezed together within the confines of the nanoscale particles.

In 2004, Los Alamos researchers Richard Schaller and Klimov reported the first observations of strong carrier multiplication in nanosized crystals of lead selenide resulting in up to two electron-hole pairs per absorbed photon. A year later, Arthur Nozik and coworkers at the National Renewable Energy Laboratory reproduced these results. Eventually, spectroscopic signatures of carrier multiplication were observed in nanocrystals of various compositions, including silicon.

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