Quantum dots could make solar panels more efficient

New studies conducted by researchers at the Colorado School of Mines could significantly improve the efficiency of solar cells.

Mark Lusk and his colleagues' latest work describes how the size of light-absorbing particles -- quantum dots -- affects the particles' ability to transfer energy to electrons to generate electricity.

The advance provides evidence to support a controversial idea, called multiple-exciton generation (MEG), which theorises that it is possible for an electron that has absorbed light energy, called an exciton, to transfer that energy to more than one electron, resulting in more electricity from the same amount of absorbed light.

Quantum dots are man-made atoms that confine electrons to a small space. They have atomic-like behaviour that results in unusual electronic properties on a nanoscale. These unique properties may be particularly valuable in tailoring the way light interacts with matter.

For this study, Lusk and collaborators used a National Science Foundation (NSF)-supported high performance computer cluster to quantify the relationship between the rate of MEG and quantum dot size.

They found that each dot has a slice of the solar spectrum for which it is best suited to perform MEG and that smaller dots carry out MEG for their slice more efficiently than larger dots. This implies that solar cells made of quantum dots specifically tuned to the solar spectrum would be much more efficient than solar cells made of material that is not fabricated with quantum dots.

According to Lusk, "We can now design nanostructured materials that generate more than one exciton from a single photon of light, putting to good use a large portion of the energy that would otherwise just heat up a solar cell."

The results are published in the April issue of the journal ACS Nano.