Friday, August 14, 2009

"ENERGY: Nanospears promise to supercharge solar cells"

Conventional solar cells are tuned to a particular wavelength of light--usually the red end of the visible spectrum even though almost as much sunlight is present at the blue end of the spectrum too. But by combining materials that absorb both the red and blue end of the visible spectrum, the efficiency of solar cells can be greatly improved--especially on cloudy days when most of the radiation is blue. Look for supercharged solar cells within five years.

By studding the top of solar cells with nanospears of zinc oxide (ZnO), the spectrum of light absorption can be expanded to enhance their efficiency, according to researchers at the Missouri University of Science and Technology (Rolla). The researchers grew zinc oxide on top of silicon solar cell, so that the nanoscale spears could absorb long UV wavelength while allowing the shorter IR wavelengths to pass onto the silicon, thus combining both UV and IR absorption. Since the hybrid material both absorbs and emits light, it may also find applications with ultraviolet lasers, wide-spectrum solid-state lighting and in new types of piezoelectric devices, according to the researchers. Previous attempts to grow zinc oxide atop silicon have achieved only limited success, according to Switzer, due to the lattice mismatch between the two materials. The problem was resolved by tilting the axis of the zinc oxide lattice so that it precisely matched that of silicon.