Green power from rainbows

Author: John Monczunski

Nearly three-fourths of America’s electricity is produced by burning fossil fuels that pump 2.5 billion tons of carbon dioxide into the atmosphere each year. One of the most promising ways to cut those numbers and go green, Prashant Kamat believes, is through the rainbow, as in rainbow solar cells.

A recent breakthrough by the Notre Dame professor of chemistry and biochemistry has moved this next-generation photovoltaic power cell a step closer to reality. Kamat and his colleagues have demonstrated that quantum dots, incredibly tiny nanoscale structures, can be used to create more efficient power cells that create electricity directly from sunlight.

The ND chemist was able to attach cadmium selenide quantum dots to a film of titanium dioxide particles. When light strikes the surface, the quantum dots absorb the light energy, causing them to inject electrons into the titanium dioxide. The electrons then are collected at an electrode, thus producing electric current.

Since quantum dots come in varying sizes, and since these different sizes absorb different wavelengths of light, Kamat’s breakthrough opens the door to the creation of a rainbow solar power cell made by stacking quantum dots of varying sizes. Smaller-sized quantum dots at the outer edge of the assembly absorb blue light, while red light passes through and is absorbed by larger quantum dots in the inner layers. Such a rainbow solar cell would be more efficient, Kamat explains, because it would be able to harvest a greater portion of the light spectrum than conventional solar power cells.

Kamat has demonstrated that the efficiency of solar cells can be increased even more by incorporating carbon nanotubes into the structure. The tiny tubes facilitate electron transfer in the solar power cell.

John Monczunski is an associate editor of this magazine.