By Gopal R. Rao
Scientists have found a way to siphon off the 'hot' electrons that are responsible for much of the energy lost in current solar cells. The research could lead to the development of far more efficient photovoltaic materials - theoretically doubling the proportion of solar energy that can be converted into electric power.
In current silicon solar cells, only around a third of the energy that hits the cell is converted into electricity. Much of the energy delivered by the incoming photons is lost as heat - so-called hot electrons are generated, which cool extremely rapidly. Thus, their energy cannot easily be put to good use.
Now a research team has used a combination of nanomaterials and titanium dioxide to capture the hot electrons. The authors suggest that this is the first time it has been demonstrated that hot electrons can be taken out from a nanomaterial.
Interestingly, hot electrons are known to stay hot for longer in nanomaterials, giving just enough time - hundreds as opposed to only a few picoseconds - to capture them. The team deposited semiconducting lead selenide nanocrystal quantum dots on titanium dioxide, an electron conductor, and used optical second harmonic generation to 'watch' the hot electrons moving across the interface between the two materials.
Though the authors have not built an actual solar cell incorporating these materials, they estimate that their method might eventually make it possible to increase efficiency to 66 per cent.
Transfer from Semiconductor Nanocrystals
Science 18 June 2010: Vol. 328. no. 5985, pp. 1543 - 1547. DOI: 10.1126/science.1185509
Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)